1978 , Volume , Issue May-1978

1978 , Volume , Issue May-1978

. i n n

© Copr. 1949-1998 Hewlett-Packard Co.

mam

Microprocessor-Controlled Harmonic

Heterodyne Microwave Counter also

Measures Amplitudes

T h e n e w h a r m o n i c h e t e r o d y n e f r e q u e n c y m e a s u r i n g technique provides wide F M tolerance, high sensitivity, and automatic amplitude discrimination. Simultaneous measurement of input amplitude is optional.

by Ali Bologlu and Vernon A. Barber

AUTOMATIC MICROWAVE FREQUENCY mea surements to 18 GHz and beyond have generally been done using one of two frequency down-conver sion techniques, the transfer oscillator or the hetero dyne converter (see box, page 5). In a new micro wave counter, Model 5342 A (Fig. 1), a new down- conversion technique, called harmonic heterodyne conversion, provides many of the advantages of both traditional methods while significantly reducing cost. Among these advantages are wide FM tolerance, high input sensitivity, and automatic amplitude dis crimination.

The new technique requires only one microwave component, a sampler, and relies on a microprocessor to perform the required computations, thereby eliminating a good deal of digital hardware and its associated expense. The microprocessor also adds to the counter's power and versatility by making it pos sible to manipulate the measured data. An easy-to-use keyboard permits the operator to define frequency o f f s e t s o r m e a s u r e f r e q u e n c y d e v i a t i o n s . A n amplitude measurement option provides simultane ous measurements of input signal level and input frequency for the first time in a microwave counter.

Model 5342A measures frequency from 10 Hz to 18

GHz with a resolution of 1 Hz. It has an 11-digit display. With the amplitude measurement option, the user can see input level displayed in dBm with 0.1-dB resolution and ±1.5-dB accuracy, and frequency can be displayed simultaneously with 1-MHz resolution.

Harmonic Heterodyne Conversion

Fig. 2 is a simplified block diagram of the harmonic heterodyne technique. All of the harmonics of an internal oscillator are simultaneously mixed with the unknown signal by the sampler. The output of the sampler consists of sum and difference frequencies produced by each harmonic of the internal oscillator mixing with the unknown. The internal oscillator, a programmable frequency synthesizer locked to the counter's time base, is incremented in frequency until one of the outputs of the sampler is in the counting range of the low-frequency counter. The IF detector detects when the IF (intermediate frequency) is in the range of the low-frequency counter and sends a signal that causes the synthesizer control to stop increment ing the frequency of the synthesizer. The IF is then counted by the low-frequency counter. The unknown frequency can be determined from the relation:

C o v e r : A n e a s y - t o - u s e k e y b o a r d p u t s t h e m i c r o p r o c e s s o r - b a s e d M o d e l 5 3 4 2 A

M i c r o w a v e F r e q u e n c y C o u n t e r t h r o u g h i t s p a c e s . T h i s n e w c o u n t e r m e a s u r e s f r e q u e n c i e s a n d ( o p t i o n a l l y ) a m p l i t u d e s , w i t h o r w i t h o u t o f f s e t s , u p t o 1 8 G H z , a n d has extensive built-in self-test facilities.

In this Issue:

M i c r o p r o c e s s o r - C o n t r o l l e d H a r m o n i c

H e t e r o d y n e M i c r o w a v e C o u n t e r a l s o

M e a s u r e s A m p l i t u d e s , b y A l i B o l o g l u

a n d V e r n o n A . B a r b e r p a g e 2

A Technique that Is Insensitive to FM for Deter mining Harmonic Number and Sideband, by

Luiz Peregrino, page 13.

Generating High-Speed CRT Displays from Digital Data, by Arnot L Ellsworth a n d K u n i o H a s e b e .

page 17

L a b o r a t o r y N o t e b o o k

S w e p t - F r e q u e n c y M e a s u r e m e n t s o f H i g h

Levels of Attenuation at Microwave Frequencies

page 24

 © H e w l e t t - P a c k a r d C o m p a n y . 1 9 7 8

Printed in U.S.A.

© Copr. 1949-1998 Hewlett-Packard Co.

where fx = unknown frequency

N = harmonic of frequency synthesizer fj = programmed frequency of synthe sizer fIFl = IF produced by Nf: mixing with fx.

The frequency fa of the programmable synthesizer is known, since it is known where the indexing of the

Input

Sampler

Driver

IF

Detector

F i g . 1 . M o d e l 5 3 4 2 A M i c r o w a v e

F r e q u e n c y C o u n t e r m e a s u r e s f r e q u e n c i e s f r o m 1 0 H z t o 1 8 G H z .

W i t h i t s a m p l i t u d e m e a s u r e m e n t option, it can simultaneously mea s u r e a n d d i s p l a y f r e q u e n c y a n d a m p l i t u d e . K e y b o a r d c o n t r o l a n d m i c r o p r o c e s s o r a r c h i t e c t u r e p r o v i d e e a s e o f o p e r a t i o n a n d d a t a manipulation features.

synthesizer was stopped. fIFl is known, since it is counted by the low-frequency counter. Still to be de termined are N and the sign ( ±) of the IF. This is done by making one more IF measurement with the syn thesizer frequency offset from its previous value by a known amount Af. Thus f2 = fj-Af. This produces an IF, fIF2, that is counted by the low-frequency counter. The offset Af is much smaller than the IF, so if fx is less than Nf1( then fIFl produced by mixing

Nfj with fx will be greater than fIF2. Conversely, if fx is greater than Nfj then fIF1 will be less than f]F2.

This is shown in Fig. 3. N is then determined as follows: fIF1 =

- f x ( N f ^ f J

= Nf2-fx (Nf2>fx)

Programmable

Frequency

Synthesizer

Synthesizer

Control

N =

MF2

Fig. 2. Simplified block diagram of the harmonic heterodyne frequency conversion technique used in the 5342 A Counter.

All harmonics of a frequency synthesizer are simultaneously m i x e d w i t h t h e u n k n o w n i n a s a m p l e r . T h e s y n t h e s i z e r f r e quency is incremented until one of the sampler outputs is in the range of the low-frequency counter. The system measures this output, determines which synthesizer harmonic produced it, a n d a d d s t h e m e a s u r e d v a l u e t o t h e k n o w n h a r m o n i c f r e quency. A microprocessor controls the synthesizer and does the computations.

or, if fx is greater than Nf1( f IF1

Nf, (Nf,<fx

IF2

= fx - Nf2 (Nf2<fx

N =

MFl

The unknown frequency is then computed as follows:

© Copr. 1949-1998 Hewlett-Packard Co.

f x = N f j - f I F l ( f , F 2 < f , F 1 )

fx =

Nfa IF1 (fI IF2 f,

IFlJ

Since the frequency of the synthesizer is known to the accuracy of the counter's time base and the IF is mea sured to the accuracy of the counter's time base the accuracy of the microwave measurement is deter mined by the time base error and the ±l-count error inherent in any counter.

Automatic Amplitude Discrimination

The bandwidth and gain characteristics of the IF provide automatic amplitude discrimination. This means that the counter will measure the frequency of the highest-level signal in the presence of a multitude of signals at different frequencies, provided that the desired signal is larger than any other by a certain minimum number of dB. The specified minimum separation for the 5342Ais 6 dB for signals within 500

MHz of the desired signal and 20 dB for signals farther away. Typical values are lower.

FM Considerations

The discussion up to now has dealt with the ideal case in which the counter is measuring input signals with little or no FM. However, many signals in the microwave region, particularly those from micro wave radios, have significant modulation on them.

To prevent this modulation from causing incorrect computation of the harmonic number N, the har monic heterodyne technique is implemented as shown in Fig. 4. There are two synthesizers offset by precisely 500 kHz, two counters, and a pseudo random sequence generator that controls a multi plexer and the two counters synchronously.

N f ,

r f

f x N f ,

N f , f

F i g . 3 . T o d e t e r m i n e t h e n u m b e r , N , o f t h e s y n t h e s i z e r h a r m o n i c t h a t p r o d u c e d t h e s a m p l e r o u t p u t a t i n t e r m e d i a t e f r e quency f¡F1, the counter makes a second measurement with t h e s y n t h e s i z e r f r e q u e n c y f - , c h a n g e d t o f 2 = f - , - A f , w h e r e

& f  « f I F 1 . I f f x < N f - ! t h e n 1 , F 2 < 1 , F i , a n d i f f x > N f 1 t h e n

fiF2>fiFi> as shown here. Then N = \fIF1 —fiF2\ -=-Af.

Input

Multiplexer

Frequency

Synthesizers

Main

Fig. 4. The harmonic heterodyne technique is implemented in the 5342A Counter with two synthesizers and two counters, as shown here, to prevent frequency modulation on the unknown signal from causing an incorrect computation of the harmonic n u m b e r N . A p s e u d o r a n d o m s e q u e n c e g e n e r a t o r s w i t c h e s b e t w e e n t h e t w o s y n t h e s i z e r s a n d t h e t w o c o u n t e r s .

Pseudorandom switching avoids any coherence between the s w i t c h i n g r a t e a n d t h e m o d u l a t i o n r a t e o f t h e F M o n t h e u n known.

The operating algorithm is as follows. With the multiplexer having selected the main oscillator out put, the main oscillator frequency fl is swept from

350 MHz to 300 MHz in 100-kHz steps. The offset oscillator frequency f2 is maintained at ft - 500 kHz by a phase-locked loop. When the IF detector indi cates the presence of an IF signal in the range of

50 MHz to 100 MHz, the synthesizer stops its sweep and the counter starts the harmonic number (N) deter mination. The pseudorandom sequence output switches between the main oscillator and the offset oscillator and between counter A and counter B so that counter A accumulates fIF1 (produced by Nfa mixing with fx) and counter B accumulates fiF2 (pro duced by Nf2 mixing with fx). The pseudorandom switching prevents any coherence between the switching rate of the multiplexer and the modulation rate of the FM that might produce an incorrect com putation of N. N and the sign of the IF are computed as previously described, since counter A accumulates f¡F1) and counter B accumulates fjF2. The pseudoran dom sequence is then disabled, the main oscillator is selected, and the frequency of fIFl is measured in counter A to the selected resolution.

The counter's FM tolerance is related to the length of the pseudorandom sequence. As shown in the box on page 13, the maximum error in the determina-

© Copr. 1949-1998 Hewlett-Packard Co.

Down-Conversion Techniques for

Microwave Frequency Measurements

A frequency counter is limited in its direct-counting frequency range by the speed of its logic circuitry. Today the state of the art i n h i g h - s p e e d l o g i c a l l o w s t h e c o n s t r u c t i o n o f c o u n t e r s w i t h a frequency range of around 500 MHz. Continuing advances in 1C technology should extend this range beyond 1 GHz in the not- too-distant future.

The designer of an automatic microwave counter must look to s o m e f o r m o f d o w n - c o n v e r s i o n t o e x t e n d f r e q u e n c y m e a s u r e ment beyond 500 MHz. Four techniques are available today to provide this down-conversion:1

â € ¢ P r e s c a l i n g , o r s i m p l y d i v i d i n g t h e i n p u t f r e q u e n c y , w i t h a range of only about 1.5 GHz;

• Heterodyne converter, allowing measurements as high as 20

GHz;

• Transfer oscillator, used in counters with ranges to 23 GHz;

• Harmonic heterodyne converter, a new technique that can p r o v i d e m e a s u r e m e n t s t o 4 0 G H z , a n d i s u s e d i n t h e n e w

M o d e l 5 3 4 2 A M i c r o w a v e F r e q u e n c y C o u n t e r t o m e a s u r e u p to 18 GHz.

Heterodyne Converter

In a heterodyne converter, the incoming microwave signal is mixed with a high-stability local oscillator signal of known fre quency, resulting in a difference frequency within the range of a conventional counter (see Fig. 1). The high-stability local oscil l a t o r s i g n a l i s g e n e r a t e d b y f i r s t d i g i t a l l y m u l t i p l y i n g t h e f r e quency of the instrument's time base to a convenient fundamen tal frequency, fin, typically 1 00 to 500 MHz. This fin is directed to a harmonic generator that produces a comb line of frequencies s p a c e d a t f i n e x t e n d i n g t o t h e f u l l f r e q u e n c y r a n g e o f t h e c o u n t e r . O n e l i n e o f t h i s c o m b , K f i n , i s t h e n s e l e c t e d b y a m i c r o w a v e f i l t e r a n d d i r e c t e d t o t h e m i x e r . E m e r g i n g f r o m t h e m i x e r i s a n i n t e r m e d i a t e f r e q u e n c y e q u a l t o f x - K f i n . T h i s f r e q u e n c y i s a m p l i f i e d a n d s e n t t o t h e c o u n t e r . T h e d i s p l a y c o n tains the sum of the intermediate frequency and Kfin.

I n p r a c t i c e , t h e s y s t e m b e g i n s w i t h K = 1 a n d s t e p s t h e m i crowave filter through the comb line until a detector indicates that an intermediate frequency in the proper range is present.

The microwave filter may be a YIG filter or an array of thin-film filters that are selected by PIN diode switches.

Fig. 2. Transfer oscillator.

harmonic member N. The counter then measures ft, multiplies by N (usually by extending its gate time) and displays the result.

Harmonic Heterodyne Converter

The harmonic heterodyne converter, as its name implies, is a h y b r i d o f t h e p r e v i o u s t w o t e c h n i q u e s . F i g . 2 o n p a g e 3 i s a simplified diagram of a counter that uses harmonic heterodyne conversion. The input fx is directed to a sampler, with the result i n g d o w n - c o n v e r t e d v i d e o s i g n a l f , F = f x - N f 1 a m p l i f i e d a n d s e n t t o t h e c o u n t e r . T h e s a m p l i n g f r e q u e n c y ^ i s c r e a t e d b y a processor-controlled synthesizer.

The acquisition routine for this down-converter consists of tun i n g t h e a f r e q u e n c y f - , u n t i l t h e s i g n a l d e t e c t o r f i n d s a v i d e o b y f ! F o f t h e a p p r o p r i a t e f r e q u e n c y r a n g e ( d e f i n e d b y the bandpass filter). Next, the harmonic number N must be deter mined, as in the transfer oscillator. One method of finding N is to u s e a s e c o n d s a m p l e r l o o p o r s i m i l a r t e c h n i q u e . A s e c o n d method is to step the synthesizer back and forth between two c l o s e l y - s p a c e d f r e q u e n c i e s a n d o b s e r v e t h e d i f f e r e n c e s i n counter readings; it is then a simple task for the processor to calculate N.

A f r e q u e n c y m e a s u r e m e n t i s a c c o m p l i s h e d b y t h e p r o c e s sor's multiplying the known synthesizer frequency fj by N, add i n g t h e r e s u l t t o t h e f r e q u e n c y f ! F m e a s u r e d b y t h e c o u n t e r , and displaying the answer: fx=Nf1+f|F.

T h e h a r m o n i c h e t e r o d y n e c o n v e r t e r h a s t h e p o t e n t i a l t o b e c o n s t r u c t e d a t a l o w e r c o s t t h a n t h e p r e v i o u s t w o t e c h n i q u e s b e c a u s e i t c a n b e d e s i g n e d w i t h j u s t o n e m i c r o w a v e c o m p o nent, the sampler, and the control, decisions, and calculations c a n b e p e r f o r m e d b y a l o w - c o s t m i c r o p r o c e s s o r .

Comparison

The table below compares the three major down-conversion techniques.

•4 —

L o c a l

O s c i l l a t o r

Harmonic

Generator

Multiplier

F i g . 1 . H e t e r o d y n e c o n v e r t e r .

Transfer Oscillator

The transfer oscillator (Fig. 2) uses the technique of phase locking a low-frequency voltage-controlled oscillator (VCO) to the microwave input signal. The VCO frequency f-| can then be measured in a conventional counter, and all that remains is to d e t e r m i n e t h e h a r m o n i c r e l a t i o n s h i p b e t w e e n t h a t f r e q u e n c y and the input. A second VCO is often used to help determine the

Reference

1 . "Fundamentals of Microwave Frequency Counters," HP Application Note 200-1 .

© Copr. 1949-1998 Hewlett-Packard Co.

tion of the harmonic number N is

Allowed Range of

IF Frequencies

2 5 M H z 5 0 M H z

1 0 0 M H z 1 2 5 M H z

Fig. 5. 5342A Counter's FM tolerance is determined by the IF bandwidth, which is 25 to 125 MHz. The IF detector stops the s w e e p w h e n t h e I F i s b e t w e e n 5 0 a n d 1 0 0 M H z . T h u s t h e a l l o w a b l e F M i s 5 0 M H z p e a k t o p e a k .

where P is the length of the pseudorandom sequence in clock periods, Afx is the peak frequency deviation of the unknown, and Af is the frequency offset be tween the two synthesizers. For example, if P = 215-1,

Afx = 5 MHz, and Af = 500 kHz, emax <0.2209. As long as emax <0.5, N is correctly determined.

The length of the pseudorandom sequence also affects the counter's measurement time, which con-

Data Bus and

Address Bus

10 Hz-500 MHz

Time Base

Buffer

Assembly

Mixer/

Search Control

Assembly

Fig. sampler, This block diagram. Only one microwave component, the sampler, is needed. This h e l p s r e d u c e c o s t .

© Copr. 1949-1998 Hewlett-Packard Co.

sists of three components: sweep time, N determina tion time, and gate time. The sweep time is 150 milli seconds or less and the gate time for 1-Hz resolution is one second. In normal operation the pseudoran dom sequence length is 360 milliseconds, so the total measurement time is about IVi seconds. Under these conditions the counter can tolerate 20 MHz peak-to-peak frequency deviation on the unknown.

This corresponds to the bandwidth of most tele communications channels.

The counter's maximum FM tolerance is deter mined by the bandwidth of the IF amplifier. As Fig. 5 shows, the allowable range of intermediate frequen cies is 25 to 125 MHz. The IF detector is adjusted to stop the sweep when the IF is in the range 50 to 100

MHz. Therefore, a maximum of 50 MHz peak-to- peak frequency deviation on the unknown can be tolerated. A switch on the rear panel of the 5342A selects either the 20-MHz or the 50-MHz FM mode.

In the wide FM mode the pseudorandom sequence length is 2096 milliseconds, so the acquisition time is significantly increased over the normal mode.

Counter Design

The overall 5342A block diagram is shown in Fig.

6. The product design not only decreases assem bly costs but also yields significant RFI performance improvements. As can be seen in Fig. 7, the entire counter is built into one die casting. The boards that constitute the individual assemblies plug into one multilayer motherboard, thereby eliminating all

IF Output

100

50

T

N

RF Input

V

+«-

1.8 pF

1.8 pFI

100 100

\\\\\Y

100

IF Output

Microstrip

/ B a l u n

Pulse

Input

Direct

Input

Amplifier

Gate Time and

PRS Generation Board

IF Amplifiers and Signal-Present

Detectors

Main Synthesizer and Offset Loop

Counter

Board

Processor

Board

H P - I B B o a r d

Option

Board

Amplitude

Option

Power

Supply

Time Base

Buffer

RF Multiplexer

JF Preamplifier

F i g . 7 . P r o d u c t d e s i g n m i n i m i z e s a s s e m b l y c o s t s a n d i m p r o v e s R F I p e r f o r m a n c e . A s i n g l e c a s t i n g h o u s e s a l l a s semblies, which plug into a single multilayer motherboard.

1 5 0

1 0 0

F i g . 8 . S a m p l e r i s a t h i n - f i l m h y b r i d c i r c u i t . T h e s a m p l i n g p u l s e c o u p l e s t o t h e s l o t t e d l i n e t h r o u g h a b a l u n t h a t g e n e r ates two opposite-polarity pulses to drive the Schottky diodes.

wiring except for the rear-panel power connections.

The power supply is of the switching regulator type. The power supply boards are also inside the casting, but in a separate compartment, so the switch ing spikes are contained and are not permitted to in terfere with the rest of the circuitry. On the front panel a fine metallic mesh covers the LED display and attenuates emissions from this area. These pre cautions have resulted in improved RFI performance with respect to past instruments.

The casting is also the main structural element of the instrument. The side rails of the box are attached to it, and the front and rear panel assemblies are

© Copr. 1949-1998 Hewlett-Packard Co.

Signature Analysis in the 5342A

I n c o r p o r a t i n g m i c r o p r o c e s s o r c o n t r o l i n t o t h e 5 3 4 2 A M i c r o w a v e F r e q u e n c y C o u n t e r m a d e i t p o s s i b l e t o d e v e l o p a p o w e r f u l m e a s u r i n g i n s t r u m e n t a t a s u b s t a n t i a l r e d u c t i o n i n c o s t . B e s i d e s p r o v i d i n g m a n y o p e r a t i o n a l b e n e f i t s , s u c h a s keyboard entry of frequency and amplitude offsets, resolution s e l e c t i o n , a n d o f f s e t r e c a l l , m i c r o p r o c e s s o r c o n t r o l e n h a n c e s the serviceability of the 5342A by providing powerful diagnostic routines, also selectable from the front-panel keyboard , that aid the service person in fault isolation and instrument verification

( s e e F i g . 1 ) . O t h e r m i c r o p r o c e s s o r r o u t i n e s , e x e r c i s e d e v e r y time the instrument is turned on, check the health of ROMs and

RAM and display error codes if all is not well.

Despite the diagnostic aids provided by the microprocessor, p l a c i n g a m i c r o c o m p u t e r i n s i d e a s o p h i s t i c a t e d m e a s u r i n g i n s t r u m e n t a l s o i n t r o d u c e s s o m e s e r v i c e a b i l i t y p r o b l e m s . A f t e r t h e f i r s t p r o t o t y p e w a s c o n s t r u c t e d , w e d i s c o v e r e d i t w a s i m possible to isolate certain failures to a particular assembly using t r a d i t i o n a l t r o u b l e s h o o t i n g e q u i p m e n t a n d t e c h n i q u e s .

Failures involving the microprocessor assembly and the indi v i d u a l a s s e m b l i e s t h a t i n t e r f a c e t o t h e m i c r o p r o c e s s o r a s s e m bly were extremely difficult to troubleshoot. Even after hours of troubleshooting, it was uncertain whether the fault was a control failure originating on the microprocessor assembly, an interface f a i l u r e o r i g i n a t i n g o n a n a s s e m b l y ' s i n t e r f a c e w i t h t h e m i c r o p r o c e s s o r , o r a f a i l u r e i n s o m e o t h e r p a r t o f t h e i n s t r u m e n t , causing the measurement algorithm to hang up or branch to an i n c o r r e c t p r o g r a m s e g m e n t . W e n e e d e d a q u i c k w a y t o v e r i f y p r o p e r o p e r a t i o n o f t h e m i c r o p r o c e s s o r c o n t r o l a s s e m b l y .

F o r t u n a t e l y , t h e r e w a s a s o l u t i o n w h i c h , e v e n t h o u g h t h e instrument had advanced to the prototype stage, was inexpen s i v e t o i m p l e m e n t a n d p e r m i t t e d m i c r o p r o c e s s o r v e r i f i c a t i o n and fault isolation to the component level. This technique, called s i g n a t u r e a n a l y s i s , r e l i e s o n a r e l a t i v e l y i n e x p e n s i v e t r o u bleshooting instrument — the 5004A Signature Analyzer.1

Signature Analysis

S i g n a t u r e a n a l y s i s , a s i m p l e m e n t e d i n t h e 5 0 0 4 A S i g n a t u r e

A n a l y z e r , e m p l o y s a d a t a c o m p r e s s i o n t e c h n i q u e t o r e d u c e l o n g , c o m p l e x d a t a s t r e a m s a t c i r c u i t n o d e s t o f o u r - d i g i t hexadecimal signatures. By taking the signature of a suspected circuit node and comparing it to the correct signature, which is e m p i r i c a l l y d e t e r m i n e d a n d d o c u m e n t e d i n t h e o p e r a t i n g a n d service manual, proper circuit operation is quickly verified. By p r o b i n g d e s i g n a t e d n o d e s , o b s e r v i n g g o o d a n d b a d s i g n a tures, and then tracing back along the signal flow from outputs to inputs, the cause of an incorrect signature may be discovered a n d c o r r e c t e d .

In operation, four signals must be supplied to the signature analyzer. A START signal initiates the measurement window. Dur ing this time window, DATA from a circuit node is clocked into the signature analyzer. A CLOCK signal synchronizes the data. A STOP s i g n a l t e r m i n a t e s t h e m e a s u r e m e n t w i n d o w .

There are two ways to implement signature analysis and meet t h e r e q u i r e m e n t s j u s t m e n t i o n e d i n a m i c r o p r o c e s s o r - b a s e d p r o d u c t : f r e e r u n n i n g a n d s o f t w a r e d r i v e n . I n t h e f r e e r u n n i n g method, the microprocessor is forced into an operating mode in w h i c h i t c y c l e s c o n t i n u o u s l y t h r o u g h i t s e n t i r e a d d r e s s f i e l d .

START/STOP signals are derived from the address bus lines. In software driven signature analysis, a stimulus program is stored in ROM. The stimulus program generates START/STOP signals and c a n a l s o w r i t e r e p e a t a b l e D A T A s t r e a m s o n t o t h e d a t a b u s f o r testing other assemblies connected to the microprocessor. Free r u n n i n g s i g n a t u r e a n a l y s i s h a s t h e a d v a n t a g e o f n o t r e q u i r i n g

üga yyy y as, yyy

Qffg yyy yüP

S A M P L E R A T E

Fig. 1. Nine diagnostic modes are available with the counter in AUTO mode. The SET key is pushed twice and is followed by the appropriate digit key.

SET, SET, 0: Indicates that the main synthesizer is sweeping

(SP) and that the signal has been placed in the IF (23) a n d f i n a l l y t h a t t h e h a r m o n i c d e t e r m i n a t i o n h a s b e e n m a d e ( H d ) . T h i s d i s p l a y i s s h o w n i n t h e p h o t o g r a p h .

SET, SET, 1: Displays the main synthesizer frequency, the location of the harmonic comb line (e.g., if -, harmonic i s b e l o w f x s o m u s t a d d I F r e s u l t ) , a n d t h e h a r m o n i c number N.

SET, SET, 2: Displays results of counter A accumulation dur ing acquisition.

SET, SET, 3: Displays results of counter B accumulation dur ing acquisition.

SET, SET, 4: Displays intermediate frequency being counted.

SET, SET, 5: If Option 002, amplitude measurement, is instal l e d , a s i n g l e c o r r e c t e d a m p l i t u d e m e a s u r e m e n t i s m a d e a n d h e l d .

SET, SET, 6: If Option 002, amplitude measurement is instal led, a continuous measure of uncorrected amplitude is displayed.

SET, SET, 7: When the signal is removed from the microwave port, the main synthesizer sweeps over its full range in

100-kHz steps.

SET, SET, 8: This mode is a keyboard check.

a n y R O M s p a c e f o r s t o r i n g t h e s t i m u l u s p r o g r a m . S o f t w a r e d r i v e n s i g n a t u r e a n a l y s i s h a s t h e a d v a n t a g e o f b e i n g a b l e t o e x e r c i s e a g r e a t e r p o r t i o n o f t h e i n s t r u m e n t ' s c i r c u i t r y . F o r thorough testing, both techniques could be implemented in the same instrument.

In the 5342A, lack of ROM space ruled out the software driven implementation. To implement the free running approach in the

5342A, all that was required was the addition of some switches and pull-up resistors to the microprocessor assembly. Fig. 9 on p a g e 9 s h o w s a b l o c k d i a g r a m o f t h e 5 3 4 2 A m i c r o p r o c e s s o r assembly. The shaded area contains the components added to t h e a s s e m b l y t o i m p l e m e n t f r e e r u n n i n g s i g n a t u r e a n a l y s i s .

T o c h e c k o u t t h e m i c r o p r o c e s s o r a s s e m b l y , t h e m i c r o p r o c e s s o r i s f o r c e d i n t o a f r e e r u n m o d e b y o p e n i n g t h e d a t a b u s s w i t c h e s S 1 ( t h i s p r e v e n t s d a t a o u t o f t h e R O M s f r o m altering the forced free run instruction) and grounding the free

© Copr. 1949-1998 Hewlett-Packard Co.

r u n s w i t c h S 2 . W h e n S 2 i s g r o u n d e d , a c l e a r B i n s t r u c t i o n i s presented to the microprocessor data input (clear B was chosen t o m i n i m i z e t h e n u m b e r o f d i o d e s n e e d e d ) . T h i s c a u s e s t h e B accumulator to be cleared and the address to be incremented by 1 . Consequently, the address lines from the microprocessor r e p e a t e d l y c y c l e o v e r t h e e n t i r e a d d r e s s f i e l d o f t h e m i c r o p r o c e s s o r f r o m 0 0 0 0 t o F F F F . B y u s i n g t h e m o s t s i g n i f i c a n t address line as both START and STOP for the 5004A, and one phase of the microprocessor clock as the 5004A CLOCK input, repeatable, stable signatures are obtained for the microproces s o r a d d r e s s l i n e s , R O M o u t p u t s , d e v i c e s e l e c t o u t p u t s , a n d most circuit nodes on the microprocessor assembly. By check ing the assembly's outputs for correct signatures (documented i n t h e m a n u a l ) , i t i s p o s s i b l e t o v e r i f y w i t h a h i g h d e g r e e o f confidence that the assembly is functioning properly. If a signa t u r e i s i n c o r r e c t , t h e n s i g n a t u r e s a r e c h e c k e d b a c k a l o n g t h e signal flow paths, from outputs to inputs. When a device is found where the output signature is bad but the input signatures are g o o d ; t h a t d e v i c e i s r e p l a c e d .

Reference

1 . A.Y. Complex "Easy-to-Use Signature Analyzer Accurately Troubleshoots Complex

Logic Circuits," Hewlett-Packard Journal, May 1977.

-Martin Neil

bolted onto the side rails.

The only microwave component required to make the frequency measurements is the sampler, Fig. 8.

This consists of a thin-film hybrid mounted in an aluminum package that is manufactured by a hobbing die. This technique is similar to coin minting and results in relatively low piece costs.

Operation of the sampler is similar to that of samplers used in previous HP microwave counters.1

On the hybrid are two Schottky diodes placed across a slotted line. The sampling pulse couples to the slotted line through a stripline balun that generates two opposite-polarity pulses to drive the diodes. The down-converted signal is taken from two isolated resistors to the preamplifier. Resistors across the slot are used to absorb secondary reflections introduced

To Rear-Panel

Connector

F i g . a r e a f o r m i c r o p r o c e s s o r a s s e m b l y . C o m p o n e n t s i n t h e s h a d e d a r e a w e r e a d d e d f o r troubleshooting by signature analysis. Only a few switches and pull-up resistors were required.

© Copr. 1949-1998 Hewlett-Packard Co.

by the sampling pulse.

Microprocessor Architecture

Measurement, control, and system coordination of the 5342A are implemented by a 6800 microproces sor. The microprocessing unit (MPU) handles inter facing to the analog circuits, the power-up routine, display control, keyboard manipulation and control, frequency and amplitude measurements, arithmetic calculations, and diagnostics (Figs. 9, 10, 11). The

MPU consists of one 6800 chip, 128 bytes of RAM

(random-access memory), and three 2K-byte ROMs

(read-only memories) that store the MPU programs.

Decoder/drivers for peripheral circuit interfaces and diagnostic switches to facilitate signature analysis for trouble shooting are also located on the processor board. A ribbon cable transports the address, data,

Start

4

R A M C h e c k

and necessary control lines to the rear panel for inter facing to external devices. During the power-on cycle, the 6800 first does a RAM exercise by doing a READ/

WRITE for each memory location using four different patterns. In hexadecimal code the four patterns are

FF, 00, AA, and 55. Should a particular location not pass, the front-panel display shows all "E"s. After the

RAM test the 6800 goes through a ROM checksum routine. A defective ROM results in a display of 1, 2, or 3 on the front panel, indicating the failed ROM.

Successful completion of the above steps causes the instrument to light up all display segments and front-panel LEDs, giving the user a visual check. The instrument then comes on in the auto mode, with

1-Hz resolution and the HP-IB interface cleared.

Keyboard input is connected to the MPU interrupt line. When a key is pushed the MPU consults a key table, branches to the proper key sequence routine, and displays a prompt. If the sequence is not com pleted, some of the key lights will be kept blinking, indicating that the routine is waiting for more key depressions to complete the sequence. If an unex pected key is pushed it may be ignored or an error indication may be displayed, depending on the situa-

ROM Check

T

Display o

Check

IF Auto Mode

Start

Decrease

Synthesizer

Frequency 500 kHz

Display

'0"=No Input

No

Add 500 kHz

To Synthesizer

Frequency

IF Manual or Low-Range Mode

F i g . 1 0 . S i m p l i f i e d 5 3 4 2 A s y s t e m f l o w c h a r t .

1 0

© Copr. 1949-1998 Hewlett-Packard Co.

F i g . 1 1 . 5 3 4 2 / 4 s w e e p f l o w c h a r t .

Yes

d B m

- 2 0 -

- 2 5

- 3 0 -

I I I I I I I I I I I I I I I I I I I ,

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 f ( G H z )

F i g . 1 2 . S p e c i f i e d a n d t y p i c a l 5 3 4 2 A i n p u t s e n s i t i v i t y .

lion. Software diagnostic routines are built in as a service aid, enabling the user to diagnose problems to the subassembly level. Digital board troubleshooting can be done to the component level using signature analysis (see page 8).

Front-Panel Inputs and Controls

The 5342A has two inputs, one going from 10 Hz to

520 MHz, and the other from 500 MHz to 18 GHz.

Sensitivity of the microwave input is shown in Fig.

12. The right-hand side of the front panel deals with input signal channel selection and sample rate con trol of the measurement. The left-hand side of the front panel enables the user to do data manipulation by keyboard control of the processor. Instructions on how to do this are on a label (Fig. 13) that is affixed to the instrument top.

The panel layout is in algebraic notation. Panel operation closely resembles remote programming via the HP interface bus (HP-IB). When the machine pow ers up it is in the auto mode with 1-Hz resolution. As the user selects other resolutions, insignificant zeros are truncated. Display digits are in groups of three to facilitate reading.

In case the user wants to bypass the acquisition cycle of the algorithm, a manual mode of operation is available. In this mode, the user should know the unknown frequency within 50 MHz and enter it via the keyboard. The counter then acts like a receiver making frequency measurements.

Offsets can be specified from the front panel. Any frequency offset can either be subtracted from or added to the measured frequency. In the auto offset mode of operation the counter holds the initial mea surement and then displays all succeeding measure ments as deviations about the initial reading.

Amplitude Measurements

Equipped with the amplitude measurement option, the 5342A is alone among microwave counters in its ability to make simultaneous amplitude and fre quency measurements. Incoming signal amplitude is measured to 0.1-dB resolution with a specified accu racy of ±1.5 dB. Amplitude offsets can be entered from the front panel in the same way as frequency offsets.

The most fundamental decision involved in de signing an amplitude measuring system was what element to use to sense amplitude. Ideally, we wanted a system that is RMS-responding from -30 to +20 dBm, makes measurements rapidly, has stable cali bration, is burnout resistant, and has low input SWR.

One choice might have been to use the counter's sam pler and measure its output level. Unfortunately, this

IF level is also a function of the input frequency, of the intermediate frequency, and of the sampler drive pulse amplitude and frequency, and begins to satu rate at about —10 dBm. Some sort of switchable at tenuator ahead of the sampler to increase dynamic range would have resulted in an input SWR greater than three at low levels. Among other alternatives, thermistors are subject to drift and easy burnout, and while thermocouples do not suffer these problems, their sensitivity is low, necessitating a narrow video bandwidth and consequent slow response at low levels. Point-contact diodes are sensitive, wideband, and have the low origin resistance necessary for driv ing an operational amplifier without biasing, but they are not very rugged, mechanically and electrically, nor are they stable over long periods. Planar Schottky diodes have recently been built, however, with low barrier height, so they are usable without bias. These

5 3 4 2 A K E Y B O A R D O P E R A T I N G I N S T R U C T I O N S

E KEA SU«e «fi NT S (OPI»

: D. D . in»o.n««i ,D

u-»» B.tr-!fmnttB.°ff,

: D. a , """'.«i^a, i à - - p  « f s s - D . Q . f f l H E . D :

*L- ANALOG CONVÉ H TE B {OPTION t*

F i g . 1 3 . I n s t r u c t i o n s f o r u s i n g t h e f r o n t - p a n e l k e y b o a r d a r e attached to each instrument. Frequency and amplitude offsets are easily specified.

© Copr. 1949-1998 Hewlett-Packard Co.

tors are identical and their outputs are independent of frequency. Therefore

VRF = V2 = KV0

F i g . 1 4 . P l a n a r S c h o t t k y d i o d e d e t e c t o r s a r e u s e d i n t h e o p t i o n a l a m p l i t u d e m e a s u r e m e n t s y s t e m . T w o d e t e c t o r s a r e u s e d t o c o m p e n s a t e f o r t e m p e r a t u r e v a r i a t i o n s . T h e d c o u t put voltage V0 is proportional to the RF sine wave voltage as l o n g a s t h e d e t e c t o r s a r e m a t c h e d , a n d i s i n d e p e n d e n t o f temperature as long as the detectors are at the same tempera ture.

devices are like point-contact diodes, but have the stability and ruggedness of ordinary Schottky diodes.

These diodes are now in use in several HP applica tions.2'3 They meet all of our requirements except that they are not RMS-responding at levels above about

— 20 dBm. Thus we actually measure voltage but make the instrument read out in units of power, and it is accurate as long as the signal does not contain much amplitude modulation.

The diode output voltage is a function of tempera ture and must be compensated. The circuit that does this (see Fig. 14] also provides another advantage. For

Av sufficiently large, V3 = V4. Since the detector out puts are equal, their inputs must be equal if the detec

Thus V0, the dc output voltage, is proportional to the

RF sine wave voltage regardless of the transfer func tion of the detectors, as long as the detectors are matched. The output is also independent of tempera ture if the diodes are at the same temperature.

The detector output voltage at -30 dBm input is about 0.5 mV, so the dc characteristics of the differen tial amplifier are very important. The amplifier is a hybrid, laser-trimmed for low offset voltage and drift.

The low origin resistance of the detector diodes allows the amplifier bias current to be drawn through the reverse direction of the diodes without introducing appreciable offset.

To display amplitude in dBm, we need the loga rithm of V. The availability of monolithic integrating converters of 13-bit accuracy allows this function to be performed by the instrument's microprocessor instead of the usual logarithmic amplifier. The dynamic range is further increased by a switchable dc amplifier ahead of the analog-to-digital converter.

This combination allows better than 0.03-dB resolu tion at all levels and avoids the drift problems of a log amplifier. Once the processor has logged and scaled the result it uses the frequency information obtained in a previous measurement to correct the result according to a calibration table stored in memory

(more about this later).

Thin-Film Hybrid

All of the microwave components are contained in a thin-film assembly (Figs. 15 and 16). The dc block ing capacitors and all resistors are integrated on two sapphire substrates, one for the microwave detector,

CR3, and the other for the low-frequency detector,

CR4. CRl and CR2 are PIN diodes used to route the input signal either to the counter or to the detector.

F i g . 1 5 . A l l o f t h e m i c r o w a v e c o m p o n e n t s o f t h e a m p l i t u d e m e a s u r e m e n t s y s t e m a r e c o n tained in a thin-film assembly. De t e c t o r s C R 3 a n d C R 4 a r e p l a n a r l o w - b a r r i e r S c h o t t k y d i o d e s m a n u f a c t u r e d b y H P .

12

© Copr. 1949-1998 Hewlett-Packard Co.

A Technique that Is Insensitive to FM for Determining Harmonic Number and Sideband

by Luiz Peregrino

T h e b a s i c p r i n c i p l e o f a h e t e r o d y n e m i c r o w a v e c o u n t e r i s t h e u s e o f a s a m p l e r o r h a r m o n i c m i x e r t o c o n v e r t t h e h i g h - frequency signal to a low intermediate frequency (IF) that can b e c o u n t e d d i r e c t l y . B e f o r e t h e f r e q u e n c y o f t h e m i c r o w a v e s i g n a l c a n b e c o m p u t e d f r o m t h e m e a s u r e d I F t h e h a r m o n i c n u m b e r a n d t h e s i d e b a n d m u s t s o m e h o w b e d e t e r m i n e d .

O n e w a y t o d e t e r m i n e t h e h a r m o n i c a n d s i d e b a n d i s t o u s e two microwave receivers with local oscillators offset by Af. The d i f f e r e n c e b e t w e e n t h e t w o I F f r e q u e n c i e s i s p r o p o r t i o n a l t o the harmonic number and the sign of the difference determines the sideband:

F2

N =

T h e m a i n d i s a d v a n t a g e w i t h t h i s t e c h n i q u e i s t h e c o s t o f t h e two high-frequency receivers.

An alternate solution ¡s to vary the local-oscillator frequency, for instance switching regularly between two values. It can be s h o w n t h a t t h i s t e c h n i q u e w o u l d b e v e r y s e n s i t i v e t o F M p r e sent in the microwave signal.1'2

Another possibility ¡s to apply random modulation to the local oscillator and correlate the applied modulation to the resultant m o d u l a t i o n i n t h e I F . I f t h e r e i s c r o s s c o r r e l a t i o n b e t w e e n t h e applied modulation and the FM in the microwave signal, there will but an error in the determination of the harmonic number, but i f t h i s e r r o r i s l e s s t h a n 0 . 5 , i t c a n b e c o m p l e t e l y e l i m i n a t e d , because the harmonic number ¡s an integer.

I n t h e n e w 5 3 4 2 A M i c r o w a v e F r e q u e n c y C o u n t e r , a p s e u d o r a n d o m s i g n a l 3 ' 4 i s u s e d t o c h a n g e t h e l o c a l o s c i l l a t o r f r e q u e n c y b e t w e e n t h e v a l u e s f . , a n d f 2 a n d g a t e t h e r e s u l t a n t f,F1 and f|F2 into two low-frequency counters. This reduces the p r o b l e m t o d e t e r m i n i n g t h e p r o p e r p s e u d o r a n d o m s e q u e n c e length to give the desired FM tolerance.

L e t g ( t ) r e p r e s e n t a p e r i o d o f t h e p s e u d o r a n d o m s e q u e n c e

(see to . 1 ). When g = + 1 the local oscillator frequency ¡s set to f - , a n d f , F 1 i s g a t e d i n t o c o u n t e r 1 . W h e n g = - 1 t h e l o c a l o s cillator frequency ¡s changed to f2 and f,F2 ¡s gated into counter

2 . A t t h e e n d o f t h e s e q u e n c e , t = T , t h e d i f f e r e n c e o f t h e n u m b e r s a c c u m u l a t e d b y b o t h c o u n t e r s i s u s e d t o d e t e r m i n e t h e harmonic number.

The number M(t) accumulated by a counter ¡s given by the integral of the frequency during the time the counter ¡s gated o n . ' L e t M - | ( t ) a n d M 2 ( t ) r e p r e s e n t t h e n u m b e r s a c c u m u l a t e d b y c o u n t e r 1 a n d 2 , r e s p e c t i v e l y .

f,F1(t)dt

M i ( t ) =

= f,Fi(t)dt

/ < 2 r M f , F 2 ( t ) d t + J f I F 2 ( t ) d t + . . .

â € ¢ 1 ' 3

= /of,F2(t)dt g— 1

M

- 1

gffi

Fig. 1.

W e w i l l c o n s i d e r o n l y t h e u p p e r s i d e b a n d c a s e . T h e l o w e r s i d e b a n d c a s e i s i d e n t i c a l e x c e p t f o r a c h a n g e i n s i g n . L e t f x represent the unknown frequency and N the harmonic number.

By proper selection of IF amplifier bandwidth and local oscilla tor frequencies, we can guarantee that the harmonic and side band that be the same for both oscillator frequencies. With that in mind, we have: f,F1(t) = fx (tJ-Nf, f,F2(t) = fx (t)-Nf2

f

| f x ( t ) d t - N f J d t

J o ' g = + i J o

•f

a=-i

- N f 2 d t where T1 ¡s the length of time for which g = +1 and T2 is the l e n g t h o f t i m e f o r w h i c h g = - 1 . T h e n

N =

T , f i - T 2 f 2 r g(t)fx(t)dt

= N c + e

T h e v a l u e o f t h e i n t e g r a l i s n o t a v a i l a b l e , s o t h e s e c o n d t e r m a p p e a r s a s a n e r r o r i n t h e c a l c u l a t e d h a r m o n i c n u m b e r N c .

F o r a p s e u d o r a n d o m s e q u e n c e w e h a v e T 1 - T 2 = T C , w h e r e

T c i s t h e s e q u e n c e c l o c k p e r i o d . 3 ' 4 T h i s d i f f e r e n c e c a n b e m a d e z e r o b y a s m a l l m o d i f i c a t i o n o f t h e s e q u e n c e c i r c u i t , o r it can be disregarded if the sequence is long enough. Then we have:

T , = T 2 = T / 2

N =

2(M2-M i ) _ _ 2 _ f T

TAf T A f J n g(t)fx(t)dt.

Let us consider the error term as function of time and take the

Fourier transform. Using the shifting theorem we have:

1 3

© Copr. 1949-1998 Hewlett-Packard Co.

\<a

Af

Upper-case letters are used to represent Fourier transforms.

The term in brackets can be recognized as the Fourier transform o f t h e p s e u d o r a n d o m s e q u e n c e . T h e t e r m F x ( j a > ) / A f c a n b e considered as the input to a linear system and E(j<a) as the out put.1 The transfer function of this system is:

2 1 - e H M ' i

H(jco) =

T I j o )

JO)

To determine the counter's sensitivity to sine wave modulation present in fx(t) we only need to know | H(jw) | . This can be easily f o u n d a t f r e q u e n c i e s t h a t a r e m u l t i p l e s o f f 0 = 1 / T b y t a k i n g t h e s q u a r e r o o t o f t h e p o w e r s p e c t r u m f o r t h e r e p e t i t i v e s e quence.4

H(jn277f0)

. I T

sin —

, n > 0

QTT

P w h e r e P i s t h e s e q u e n c e l e n g t h i n c l o c k p e r i o d s :

We can use a safety factor of 2 to take care of the actual value o f | H ( f ) | f o r f r e q u e n c i e s n o t m u l t i p l e s o f f 0 . T h e w o r s t c a s e occurs for frequencies of the order of f0. For large P, we have:

4 A f ,

€max~^p A; where Afx is the peak deviation of the unknown signal.

Thus if we want the counter to tolerate 10 MHz peak FM on t h e i n p u t s i g n a l , a n d A f = 5 0 0 k H z ,

P > 2 5 , 6 0 0 .

Since P = 2m-1 , where m is the number of shift-register stages i n t h e p s e u d o r a n d o m s e q u e n c e g e n e r a t o r , a 1 5 - s t a g e s h i f t r e g i s t e r w o u l d b e n e e d e d t o g e n e r a t e t h i s s e q u e n c e .

References

1 L. Peregrino and D,W. Ricci, "Phase Noise Measurement Using a High Resolution

C o u n t e r w i t h O n - L i n e D a t a P r o c e s s i n g , " P r o c e e d i n g s o f t h e 3 0 t h A n n u a l S y m p o sium on Frequency Control, 1976, p. 309.

2 R . A . B a u g h , " F r e q u e n c y M o d u l a t i o n A n a l y s i s w i t h H a d a m a r d V a r i a n c e , " P r o c e e d i n g s o f t h e F r e q u e n c y C o n t r o l S y m p o s i u m , A p r i l 1 9 7 1 , p p . 2 2 2 - 2 2 5 .

3 . S . W . G o l o m b , " S h i f t R e g i s t e r s , " H o l d e n - D a y I n c .

4. S.W. Prentice- et al., "Digital Communications with Space Applications," Prentice-

Hall, 1964,

Luiz Peregrino

b Luiz Peregrino received the de-

^ ^ _ _ g r e e E n g e n h e i r o d e E l e t r o n i c a

- â € ¢ & * * * & m i B f r o m t n e l n s t i t u t o T e c n o l à ³ g i c o d a

Aeronáutica in Sao Paolo, Brazil in

1959. In 1960 he joined HP's mar keting organization for a brief period, then spent three years with o t h e r c o m p a n i e s a s a d e v e l o p m e n t e n g i n e e r a n d f i e l d e n g i n e e r before rejoining HP in 1964. Luiz has been involved in production, research, -and development for many HP products. He originated t h e r a n d o m m o d u l a t i o n c o n c e p t

• fvi for harmonic determination used i n t h e 5 3 4 2 A . H e ' s a m e m b e r o f I E E E . H e e n j o y s s k i i n g a n d s w i m m i n g , a n d i s a h o m e c o m p u t e r e n t h u s i a s t .

MM

Inductors Ll to L3 act as RF chokes at high frequen cies and as part of a 500-MHz high-pass filter with the capacitors Cl to C3 at lower frequencies. This repre sents an almost lossless method of injecting bias into a broadband, planar circuit.

Detectors CR3 and CR4, as mentioned above, are planar, low-barrier Schottky diodes manufactured by

HP. They are mounted with their bypass capacitors on a common metal substrate for close thermal match ing.

Since low SWR is important for an amplitude mea surement, careful attention was paid to parasitic reac tances and impedance matching. Fig. 17 shows typi cal SWR in amplitude mode, including the front- panel input connector.

The amplitude measurement circuit is made to serve as an attenuator by biasing PIN diode CR2 with high current and PIN diode CRl with only about

0.4 mA. Most input energy is dissipated in the termi nation, Rl, and input SWR is low. CRl, however looks

F i g . 1 6 . T h i n - f i l m a m p l i t u d e m e a s u r e m e n t a s s e m b l y .

1 4

© Copr. 1949-1998 Hewlett-Packard Co.

like about 250 ohms and a small amount of energy

(approximately -15 dB) goes to the sampler. This function is controlled by the converted signal level in the IF. With this technique, dynamic range is in creased to +20 dBm with no danger of overloading the input sampler.

10

Frequency (GHz)

F i g . 1 7 . M o d e l 5 3 4 2 A i n p u t S W R i n a m p l i t u d e m o d e , i n cluding the front-panel connector.

Amplitude Accuracy

Many factors affect the accuracy of an amplitude measurement in the 5342A. For traceability of our standards to NBS and their application to individual instruments in production we allow 0.4 dB. There can be up to 0.1 dB error in all the digital processes.

Analog errors, such as op amp offset, modulator linearity, noise, and A-to-D converter accuracy can add a maximum of 0.3 dB. While drift with tempera ture is typically less than 0.2 dB from 0° to 50°C, we allow a maximum of 0.4 dB. The worst-case uncer tainty for all these variables together is thus ±1.2 dB.

These errors although not random, are independent and will rarely add to this value. The root-sum-of- the-squares4 uncertainty, a more realistic value of ex pected error, is less than 0.6 dB. To this value must be added mismatch uncertainty, which depends upon the SWR of both the source and load. Reference 4 contains a good discussion of this.

Low-loss cables are recommended for routing sig nals to the front panel of the 5342A. Flexible cable with repeatable insertion loss less than semi-rigid coax has recently become available5 and is very con venient to use.

Amplitude Error Correction

A feature of Model 5342 A is its ability to correct for known errors according to a stored calibration table before display. Since the microprocessor knows the frequency and measured amplitude of the input sig nal, it is possible to correct not only for the frequency response of the detector and the insertion loss of the input connector and switch but also for amplitude related errors such as mistracking between detectors.

Typical errors to be corrected are shown in Fig. 18.

Measurements such as this are made on every unit before installation and the data is stored in a PROM in much the same format as shown in Fig. 18. Curve A is stored to eight-bit resolution in 0.25-GHz increments and curve B also to eight-bit resolution in 4-dB incre ments and every 0.5 GHz. The processor uses the frequency and uncorrected amplitude of the input signal to look up the values of correction in each table and to interpolate for intermediate values. Since

Table B is normalized to the level used in Table A, the correction values are simply added together and applied to the result.

The system that collects the data to calibrate each amplitude module consists of two signal sources and four TWT (traveling wave tube) amplifiers multi plexed together, with attenuators and an output di rectional coupler and power meter under the control of an HP 9825A Desktop Computer via the HP-IB.

This system drives the module under test with all frequencies and amplitudes in its range, and with low source SWR and accurately known amplitude. The error in the response of the module is then measured and stored in the calibration PROM.

Acknowledgments

Many individuals made significant contributions to the 5342A. The single-sampler concept was first suggested by John Dukes. Tom Coates provided mi croprocessor support software and other user aids that got the project off to a running start. The sampler was the result of Jeff Wolfington's ingenious efforts.

The power supply was done by John Gliever. We were fortunate to have Yoh Narimatsu working on the synthesizers. Art Bloedorn did the IF preamps and the direct input channel and also took production en gineering responsibility for the product. Digital de sign was initiated by Chuck Howey. When Chuck

5 GHz

1

10 GHz

1

15 GHz 20 GHz

(A)

- 1 d B -

- 2 d B -

A: Errors at an Input Amplitude of 0 dBm

(B) B: Deviations from Curve A for Different Amplitudes

+ 1dB-

2 G H z -

OdB

- 1 d B -

- 1 6 - 8 0

Input Amplitude (dBm)

+ 1 6 + 2 0

i —

12 GHz

Hz

F i g . 1 8 . E a c h 5 3 4 2 A a m p l i t u d e m e a s u r e m e n t s y s t e m i s c a l i b r a t e d b e f o r e i n s t a l l a t i o n . S y s t e m a t i c e r r o r s a r e s t o r e d i n a

P R O M a n d t h e m i c r o p r o c e s s o r c o r r e c t s e a c h m e a s u r e m e n t before display.

15

© Copr. 1949-1998 Hewlett-Packard Co.

opted for a farming career, John Shing stepped in and was responsible for digital design and firmware. Spe cial thanks are due Al Foster who designed an HP-IB interface to the 6800 processor. For the amplitude- measurement option, Steve Upshinsky worked on the low frequency analog circuitry and Art Lange did all the digital work, including programming of the calib ration system. Thanks also go to Karl Ishoy for help with hybrid circuit production. 5342A product de sign was effectively done by Keith Leslie. Martin Neil, support engineer, contributed significantly in trou bleshooting concepts and manual preparation. Prod uct introduction was by Craig Artherholt. The prod uct was designed and put into production under the lab management of Ian Band and Roger Smith. S

References

1. J. Merkelo, "A dc-to-20-GHz Thin-Film Signal Sampler for Microwave Instrumentation," Hewlett-Packard Journal,

April 1973.

2. P. A. Szente, S. Adam, and R.B. Riley, Low-Bar rier Schottky Diode Detectors," Microwave Journal,

February 1976.

3. R.E. Pratt, "Very Low-Level Microwave Power Mea surements," Hewlett-Packard Journal, October 1975.

4. "Fundamentals of RF and Microwave Power Measure ment," HP Application Note 64-1.

5. D.L. Slothour, "Expanded PTFE Dielectrics for Coaxial

Cables," Plastics Engineering, March 1975.

A l i B o l o g l u

AN Bologlu has been with HP for fifteen years and has been project m a n a g e r f o r m i c r o w a v e c o u n t e r s since 1 970. He's contributed to the d e s i g n o f m a n y H P f r e q u e n c y s y n t h e s i z e r s a n d m i c r o w a v e

_ I c o u n t e r s , m o s t r e c e n t l y t h e

I 5 3 4 2 A . A l i r e c e i v e d B S a n d M S

4 f e I d e g r e e s i n e l e c t r i c a l e n g i n e r i n g i n

1 I 1 9 6 2 a n d 1 9 6 3 f r o m M i c h i g a n

^ k I S t a t e U n i v e r s i t y a n d t h e d e g r e e o f

H ^ I E l e c t r i c a l E n g i n e e r f r o m S t a n f o r d

B k ' U n i v e r s i t y i n 1 9 6 5 . B o r n i n I s t a n -

I n b u l , T u r k e y , h e ' s m a r r i e d , h a s

^ B K j t h r e e c h i l d r e n , a n d n o w l i v e s i n

Mountain View, California. He plays tennis, enjoys water sports, a n d c o a c h e s a y o u t h s o c c e r t e a m .

Vernon A. Barber

A l B a r b e r h a s b e e n d e s i g n i n g H P

I microwave counters for ten years.

- H i s l a t e s t p r o j e c t w a s t h e

I a m p l i t u d e m e a s u r e m e n t o p t i o n f o r

" the 5342A. Al was born in Chicago and grew up in Fairbanks, Alaska.

He received his BSEE degree from the University of Washington in

1967 and his MSEE from Stanford

^ University in 1970. He's a member

^ o f I E E E . A l ' s t a s t e s i n r e c r e a t i o n run to mountain climbing and classical music. He's climbed in the Sierra Nevada, the Rocky

Mountains, the Alaska Range, the

A l p s , a n d t h e H i m a l a y a , a n d h e ' s n o w l e a r n i n g p i a n o . H e ' s married and lives in San Jose, California.

I n p u t C h a r a c t e r i s t i c s

INPUT 1 :

F R E Q U E N C Y R A N G E : 5 0 0 M H z t o 1 8 G H z

S E N S I T I V I T Y : 5 0 0 M H z t o 1 2 . 4 G H z . - 2 5 d B m

1 2 4 G H z 1 0 1 8 G H z , - 2 0 d B m

M A X I M U M I N P U T : + 5 d B m ( s e e O p t i o n 0 0 2 , 0 0 3 f o r h i g h e r l e v e l )

D Y N A M I C R A N G E : 5 0 0 M H z 1 O 1 2 . 4 G H z . 3 0 d B

1 2 . 4 G H z t o 1 8 G H z , 2 5 d B

I M P E D A N C E : 5 0 o h m s , n o m i n a l

C O N N E C T O R : P r e c i s i o n T y p e N t à © m a l e

D A M A G E L E V E L : + 2 5 d B m

O V E R L O A D I N D I C A T I O N : D i s p l a y s d a s h e s w h e n i n p u t l e v e l e x c e e d s ^ 5 d B m n o m i n a l

C O U P L I N G : d o t o l o a d , a c t o i n s t r u m e n t

S W R : < 2 : 1 , 5 0 0 M H z - 1 0 G H z

O : 1 , 1 0 G H z - 1 8 G H z

F M T O L E R A N C E : S w i t c h s e l e c t a b l e ( r e a r p a n e l )

F M ( w i d e ) : 5 0 M H z p - p w o r s t c a s e

C W ( n o r m a l ) : 2 0 M H z p - p w o r s t c a s e

F o r m o d u l a t i o n r a l e s f r o m d c t o 1 0 M H z

A M T O L E R A N C E : A n y m o d u l a t i o n i n d e x p r o v i d e d t h e m i n i m u m s i g n a l l e v e l i s n o t l e s s t h a n t h e s e n s i t i v i t y s p e c i f i c a t i o n

A U T O M A T I C A M P L I T U D E D I S C R I M I N A T I O N : A u t o m a t i c a l l y m e a s u r e s t h e l a r g e s t o f a l l s i g n a l s p r e s e n t , p r o v i d i n g t h a t s i g n a l i s 6 d B a b o v e a n y s i g n a l w i t h i n 5 0 0 M H z : 2 0 d B a b o v e a n y s i g n a l , 5 0 0 M H z - 1 8 G H z .

M O D E S a n d O P E R A T I O N : A u t o m a t i c : C o u n t e r a u t o m a t i c a l l y a c q u i r e s a n d d i s p l a y s h i g h e s t l e v e l s i g n a l w i t h i n s e n s i t i v i t y r a n g e M a n u a l C e n t e r f r e q u e n c y e n t e r e d 1 0 w i t h i n ^ 5 0 M H z o f t r u e v a l u e .

A C Q U I S I T I O N T I M E : A u t o m a t i c m o d e : n o r m a l F M 5 3 0 m s w o r s t c a s e : w i d e

F M 2 . 4 s w o r s t c a s e . M a n u a l m o d e : 5 m s a f t e r f r e q u e n c y e n t e r e d .

I N P U T 2 :

F R E Q U E N C Y R A N G E : 1 0 H z t o 5 2 0 M H z D i r e c t C o u n t

S E N S I T I V I T Y : 5 0 Ã Ã . 1 0 H z t o 5 2 0 M H z , 2 5 m V r m s

1 M n , 1 0 H z t o 2 5 M H z , 5 0 m V r m s

I M P E D A N C E : S e l e c t a b l e : 1 M n . < 5 0 p F o r 5 0 ! t n o m i n a l

C O U P L I N G : a c

C O N N E C T O R : T y p e B N C f e m a l e

M A X I M U M I N P U T : 5 0 n , 3 . 5 V r m s ( - 2 4 d B m ) o r 5 V d c f u s e p r o t e c t e d : 1 M n .

200 Vdc + 5.0 Vrms

TIME BASE:

C R Y S T A L F R E Q U E N C Y : 1 0 M H z

S T A B I L I T Y - A g i n g r a t e : < 1 X 1 0 ~ 7 p e r m o n t h

S h o r t t e r m : < 1 x 1 0 ~ 9 f o r 1 s e c o n d a v g . t i m e

T e m p e r a t u r e : < 1 X 1 0 ~ 6 o v e r t h e r a n g e 0 ; C t o 5 0 C C

L i n e v a n a t j o n : < Â ± 1 x 1 0 ~ 7 f o r 1 0 % c h a n g e f r o m n o m i n a l .

S P E C I F I C A T I O N S

HP Model 5342A Microwave Frequency Counter

O U T P U T F R E Q U E N C Y : 1 0 M H z , 3 2 . 4 V s q u a r e w a v e ( T T L c o m p a t i b l e ] ; 1 . 5 V peak-to-peak ¡nto 50Ià available from rear panel BNC.

E X T E R N A L T I M E B A S E : R e q u i r e s 1 0 M H z , 1 . 5 V p e a k - t o - p e a k s i n e w a v e o r s q u a r e e i t h e r i n t o 1 k ! l v i a r e a r - p a n e l B N C c o n n e c t o r . S w i t c h s e l e c t s e i t h e r i mal ¡ - 1 aw

Optional Time Base (Option 001)

Option 001 provides an oven -control led crystal oscillator time base, 1054-1A, lhat r e s u l t s i n b e t t e r a c c u r a c y a n d l o n g e r p e r i o d s b e t w e e n c a l i b r a t i o n ,

C R Y S T A L F R E Q U E N C Y : 1 0 M H z

A g i n g r a t e : < S x I 0 ~ 1 0 / d a y a f t e r 2 4 - h o u r w a r m - u p

S h o r t t e r m : < 1 x 1 0 ~ 1 1 f o r 1 s e c o n d a v g . t i m e

T e m p e r a t u r e : < 7 x 1 0 ~ 9 o v e r t h e r a n g e 0 Â ° C t o 5 0 Â ° C

L i n e v a r i a t i o n : < 1 â € ¢ 1 0 ~ ' ^ f o r 1 0 % c h a n g e f r o m n o m i n a l

W a r m - u p : < 5 x 1 D ~ 9 o f f i n a l v a l u e 2 0 m i n u t e s a f t e r t u r n - o n , a t

25°C

Amplitude Measurement {Option 002)

O p t i o n i n c o m p r o v i d e s t h e c a p a b i l i t y o f m e a s u r i n g t h e a m p l i t u d e o f t h e i n c o m i n g s i n e w a v e s i g n a l , a n d s i m u l t a n e o u s l y d i s p l a y i n g i t s f r e q u e n c y ( M H z ) a n d l e v e l ( d B m ) . T h e m a x i m u m o p e r a t i n g l e v e l a n d t h e t o p e n d o f t h e d y n a m i c r a n g e a r e i n c r e a s e d t o + 2 0 d B m . A m p l i t u d e o f f s e t t o 0 . 1 d B r e s o l u t i o n m a y b e s e l e c t e d f r o m f r o n t - p a n e l p u s h b u t t o n s .

I N P U T 1 :

F R E Q U E N C Y R A N G E : 5 0 0 M H z - 1 8 G H z

D Y N A M I C R A N G E ( F R E Q U E N C Y A N D L E V E L ) :

- 2 2 d B m t o - 2 0 d B m , 5 0 0 M H z ! o 1 2 . 4 G H z

- 1 5 d B m t o + 2 0 d B m , 1 2 . 4 G H z t o 1 8 G H z

M A X I M U M O P E R A T I N G L E V E L : + 2 0 d B m

D A M A G E L E V E L : + 2 5 d B m

O V E R L O A D I N D I C A T I O N : D i s p l a y s d a s h e s w h e n i n p u t l e v e l e x c e e d s * 2 0 d B m

R E S O L U T I O N : 0 . 1 d B

A C C U R A C Y : Â ± 1 . 5 d B ( e x c l u d i n g m i s m a t c h u n c e r t a i n t y )

S W R : < 2 : 1 ( a m p l i t u d e m e a s u r e m e n t )

< 5 : 1 ( f r e q u e n c y m e a s u r e m e n t )

M E A S U R E M E N T T I M E : 1 0 0 m s + f r e q u e n c y m e a s u r e m e n t t i m e

D I S P L A Y : S i m u l t a n e o u s l y d i s p l a y s f r e q u e n c y t o 1 M H z r e s o l u t i o n a n d i n p u t l e v e l . ( O p t i o n 0 1 1 p r o v i d e s f u l l f r e q u e n c y r e s o l u t i o n o n H P - I B output).

I N P U T 2 : ( 5 0 1 1 i m p e d a n c e o n l y )

F R E Q U E N C Y R A N G E : 1 0 M H z - 5 2 0 M H z

D Y N A M I C R A N G E ( F R E Q U E N C Y A N D L E V E L ) : - 1 7 d B m t o + 2 0 d B m

D A M A G E L E V E L : + 2 4 d B m

R E S O L U T I O N : 0 . 1 d B

A C C U R A C Y : Â ± 1 . 5 d B ( e x c l u d i n g m i s m a t c h u

S W R : < 1 . 8 : 1

M E A S U R E M E N T T I M E : 1 0 0 m s + f r e q u e n c y m e a s u r e m e n t t i m

D I S P L A Y : S i m u l t a n e o u s l y d i s p l a y s f r e q u e n c y t o 1 M H z r input level.

E x t e n d e d D y n a m i c R a n g e ( O p t i o n 0 0 3 )

Option range provides an attenuator that automatically extends the dynamic range o f o p e r a t i o n t o r i n p u t 1 ,

I N P U T 1 :

F R E Q U E N C Y R A N G E . 5 0 0 M H z t o 1 8 G H z

S E N S I T I V I T Y : 5 0 0 M H z t o 1 2 . 4 G H z , - 2 2 d B m

1 2 . 4 G H z t o 1 8 G H z , - 1 5 d B m

D Y N A M I C R A N G E : 5 0 0 M H z t o 1 2 . 4 G H z , 4 2 d B

1 2 . 4 G H z t o 1 8 G H z , 3 5 d B

D A M A G E L E V E L : + 2 5 d B m

S W R : < 5 : 1

General

A C C U R A C Y :  ± 1 c o u n t  ± t i m e b a s e e r r o r .

R E S O L U T I O N : F r o n t - p a n e l p u s h b u t t o n s s e l e c t 1 H z t o 1 M H z .

R E S I D U A L S T A B I L I T Y : W h e n c o u n t e r a n d s o u r c e u s e c o m m o n t i m e b a s e o r counter uses external higher stability time base, <4xlo~11 rms typical.

D I S P L A Y : 1 t - d l g i t L E D d i s p l a y , s e c t i o n a l i z e d t o r e a d G H z , M H z , k H z . a n d H z .

S E L F M H z S e l e c t e d f r o m f r o n t - p a n e l p u s h b u t t o n s . M e a s u r e s 7 5 M H z f o r resolution chosen.

F R E Q U E N C Y O F F S E T : S e i e c t e d f r o m f r o n t - p a n e ! p u s h b u t t o n s . D i s p l a y e d f r e q u e n c y i s o f f s e t b y e n t e r e d v a l u e t o 1 - H z r e s o l u t i o n .

S A M P L E H O L D V a r i a b l e f r o m l e s s t h a n 2 0 m s b e t w e e n m e a s u r e m e n t s t o H O L D which holds display indefinitely.

I F O U T : d o w n - p a n e l B N C c o n n e c t o r p r o v i d e s 2 5 M H z t o 1 2 5 M H z o u t p u t o f d o w n -

OPERATING TEMPERATURE: 0°C to 50°C

P O W E R R E Q U I R E M E N T S : 1 0 0 / 1 2 0 / 2 2 0 / 2 4 0 V r m s , + 5 % , - 1 0 % . 4 8 - 6 6 H z ;

1 0 0 V A m a x .

S I Z E : 1 3 3 m m H x 2 1 3 m m W x 4 9 8 m m D ( 5 1 / * x 8 V i x 1 9 % f e i n )

W E I G H T : N e t 9 . 1 k g ( 2 0 I b ) . S h i p p i n g 1 2 . 7 k g ( 2 8 I b s ) .

PRICES $375. U.S.A.: 5342A, S4500 Options' 001. S500. 002, S1000. 003. $375.

M A N U F A C T U R I N G D I V I S I O N : S A N T A C L A R A D I V I S I O N

5 3 0 1 S t e v e n s C r e e k B o u l e v a r d

S a n t a C l a r a , C a l i f o r n i a 9 5 0 5 0 U . S . A .

16

© Copr. 1949-1998 Hewlett-Packard Co.

Generating High-Speed CRT Displays from Digital Data

A new graphics translator converts information received from a digital system by way of the HP interface bus into the a n a l o g s i g n a l s n e e d e d f o r t r a c i n g v e c t o r s a n d c h a r a c t e r s on high-resolution CRT displays.

by Arnot L. Ellsworth and Kunio Hasebe

GRAPHICAL DISPLAY of digital data is generally easier to interpret than long columns of num bers. Trends, curve shapes, maxima, and minima are much easier to perceive when data is presented in graphical form.

X-Y plotters are widely used for converting digital data to graphics, giving accurate, permanent records that encompass large amounts of data with fine detail.

There are times, however, when a plotter may be too slow. In applications that require many plots to be made in getting to the desired result, such as adjust ing a circuit for a desired response, not only is a lot of paper wasted but the time required to make all those plots may be inordinately long.

Storage CRTs provide a means of presenting graphical data more quickly than X-Y plotters. They too can present a great amount of data at one time, the amount being limited only by the resolution of the

CRT. However, if only part of the stored display needs to be updated, the entire display must be erased and all the data retransmitted to the display.

Directed-beam CRT displays, on the other hand, use a refresh memory, any part of which can be up dated without erasing data in the rest of the memory.

Hence, updating is fast, enabling a high degree of operator interaction with the digital system. Fur thermore, refreshed directed-beam displays are significantly brighter than storage-tube displays.

Unfortunately, there has been a major stumbling block to the use of directed-beam displays: the need for the user to provide interfacing to the digital sys tem. This can be especially troublesome when design and production resources needed for the interfacing are limited.

A Ready-Made Interface

The new HP Model 1350A Graphics Translator,

Fig. 1, represents a general solution to the interface problem. It accepts data supplied by way of the HP interface bus, stores the data, and repetitively gener ates the analog signals needed for tracing the speci fied vectors and characters (Fig. 2).

All that is necessary to implement a display system with the new graphics translator is to connect its outputs to a directed-beam display and its input to an

HP-IB interface for the system calculator or computer

(Fig. 3). The display needs to have full-scale deflec tion factors of one volt and at least 2-MHz response on the X and Y axes and 10-MHz response on the Z axis.

The system controller may already have an HP-IB interface since so many instrumentation systems are now being designed around the HP interface bus.

Programming is straightforward. Vectors are traced by specifying the coordinates of the vector end points.

Characters are drawn by specifying each character by a single ASCII code (lower or upper case) and the starting position of the character string.

Fast Results

The principal advantage of using the new graphics

•Hewlett-Packard's implementation of IEEE standard 488-1975, ANSI Standard MC 1 .1 , and BUS CEI.

F i g . 1 . T h e n e w M o d e l 1 3 5 0 A G r a p h i c s T r a n s l a t o r c o n v e r t s o u t p u t s f r o m d i g i t a l s y s t e m s t o a n a l o g o u t p u t s f o r d r i v i n g high-resolution, directed-beam CRT displays. It will be particu l a r l y u s e f u l f o r s y s t e m s i n v o l v i n g e n g i n e e r i n g d e s i g n , s t a t i s tics, medicine, process control, radar, and any others requir ing high-resolution graphics display.

17

© Copr. 1949-1998 Hewlett-Packard Co.

translator and a directed-beam display is the in creased system throughput rate. Where changes are being made in the data to be displayed, the effects of changes are immediately apparent. Curve fitting, for example, can be done much more quickly than with other display devices. When the system user has to make decisions related to scale factors, data limits, and so on, the interactivity and speed of response of the graphic display system shorten the time needed to configure the display parameters so the data is pre sented in the optimum form. Once the data presenta tion is optimized, an X-Y plotter connected to the

HP-IB can give a permanent record of the displayed data.

The internal 2K-word refresh memory of the new graphics translator can be partitioned into 32 files.

The data displayed from any of these files can be blanked, unblanked, or erased individually, permit ting selective erasure, an especially useful feature if standard data is to be retained for comparison with later data. Windowing, expansion, highlighting by blinking selected areas of the display, and the use of cursors are also possible.

The 50ÃÃ X, Y, and Z analog outputs can drive several displays in parallel with the same informa tion. However, four separate blanking outputs are provided so four different blanking signals can be obtained. These override the Z-axis signal generated for the displays. Thus, information intended only for certain displays in a multiple-display set-up can be blanked from the others. These blanking signals in

F i g . 2 . D i s p l a y s g e n e r a t e d b y a d i g i t a l s y s t e m u s i n g t h e M o d e l

1 3 5 0 A G r a p h i c s T r a n s l a t o r . H e w lett-Packard offers a variety of CRT displays suitable for use with the n e w g r a p h i c s t r a n s l a t o r , w i t h viewing areas ranging from 8 x 10 c m t o 3 0 x 3 5 c m .

effect "steer" the data to the appropriate displays.

Compared to the less-expensive raster display sys tems, directed-beam displays have higher resolution because vectors are traced in any direction with con tinuous lines and also because the addressing scheme enables the beam to be positioned with greater preci sion. For example, the 10-bit addresses used by the new graphics translator permit the beam to be positioned to any of the more than one million posi tions in the 1023 x 1024-point display area. Further more, updating is faster because only the vector end points need to be known — the system does not have to take time to calculate intermediate points. This speed

HP-IB

9 8 2 5 A I 8 1 6 5 A

Desktop I • Programmable

C o m p u t e r ^ H S i g n a l S o u r c e

3455A

Digital

Voltmeter

Q

1350A

Graphics

Translator

1311A

Large Screen

Display

F i g . 3 . T y p i c a l o f t h e k i n d o f s y s t e m s t h a t c a n u s e t h e n e w graphics translator advantageously is this automatic system f o r m e a s u r i n g f i l t e r r e s p o n s e i n a p r o d u c t i o n e n v i r o n m e n t

( D U T = d e v i c e u n d e r t e s t ) .

18

© Copr. 1949-1998 Hewlett-Packard Co.

Plug-In

IÓ

Module

T T

Interconnect Board

Display Board

M e m o r y D i g i t a l V e c t o r

Circuits Generation Circuits

I x

To Displays

TTL

Blanking

Ports

Character

Generator

Board

F i g . 4 . B a s i c b l o c k d i a g r a m o f t h e M o d e l 1 3 5 0 A G r a p h i c s

T r a n s l a t o r . T h e c h a r a c t e r g e n e r a t o r a n d I / O m o d u l e a r e d e signed to be easily replaced if special characters are needed and/or if the I/O format needs to be modified.

enables simulated motion studies.

How It's Organized

The internal organization of the Model 1350A

Graphics Translator is shown in the block diagram of

Fig. 4. The refresh memory contains the data to be displayed. It can store up to 2048 vectors and/or characters and, as mentioned before, can be par titioned into 32 files of any length, as long as the total file contents do not exceed the memory.

A separate character generator is included so a complete character can be generated in response to a single ASCII code. It is a separate subassembly with its own control circuitry so it can control the instru ment to some extent while drawing characters. This enables it to scale or rotate the characters. It is im plemented such that the character set can be changed for special applications.

The I/O module for the input and output of data is also a separate subassembly, allowing easy modifica tion of the I/O format. This module was designed almost completely with TTL technology to allow very fast data transfer (<2 /us/character or <20/iS/point).

Much of the TTL circuitry could have been replaced with a less-expensive microprocessor system but this would have slowed the data transfer rate signifi cantly.

Vector Generation

Among other requirements, there is an important one that the design of the vector generator had to meet: the CRT beam should be moved at the same constant rate for all vectors regardless of length and a n g l e s o t h e b e a m i n t e n s i t y w i l l b e u n i f o r m everywhere on the display.

This is difficult to do at the speeds required for a refreshed, directed-beam display. Consequently the vector generator approximates the ideal situation by using one of six tracing times and one of 32 intensity levels for each vector according to its length. This gives 6 x 32 = 192 combinations of tracing times and intensity levels to approximate the ideal constant tracing rate.

A block diagram of the vector generator is shown in

F i g . 5 . T o a s s u r e l o n g - t e r m s t a b i l i t y , d i g i t a l techniques are used right up to the line-driver amplifiers. This has resulted in very good tempera ture stability, as well as good, demonstrated reliabil ity.

Operation is as follows. The coordinates for the next vector endpoints are latched in the NEXT X,Y latches. When the system finishes tracing the present vector, the arithmetic units subtract the present X-Y position coordinates from the next position coordi nates. The results are the Ax and Ay components of the next vector.

The Ax component is right-shifted until a com parator indicates that the five left-most bit positions are filled with zeros. The number of shifts required is a gross indication of the length of the Ax component.

The same operation occurs with the Ay component, and the control circuits then select the larger of the two shifts as the designator of tracing time. Vector length determines tracing time as follows:

Vector length

1 > length > 1/2 of full screen

1/2 > length > 1/4

1/4 > length > 1/8

1/8 > length > 1/16

1/16 > length > 1/32

1/32 > length > 0

Tracing time

«48 /¿s

«24 /AS

= 12 /AS

= 6 /AS

~3 /JLS

=1.5 /is

The upper four bits of Ax and Ay are summed to obtain a five-bit number for control of the intensity level. The shifted Ax and Ay components are applied to rate multipliers that divide down the input clock rate according to the magnitudes of Ax and Ay. The divided-down clocks increment or decrement the X and Y position counters and the D-to-A converters generate analog signals proportional to the counters' instantaneous contents, moving the CRT beam through a series of microsteps to arrive at the next position (three-pole low-pass filters in the drive amplifiers smooth the microstep transitions). When the control circuits determine that the correct number o f c l o c k s h a v e o c c u r r e d , t h e r a t e m u l t i p l i e r s are stopped.

Operation with the character generator is similar

1 9

© Copr. 1949-1998 Hewlett-Packard Co.

From Refresh Memory or Character Generator

Present X Position

To/Froml

Controls

Board |

Intensity Control

To Z-Axis Circuits

Fig. processing performed block diagram of the vector generator. All processing is performed digitally to eliminate drift. The coordinates of the instantaneous CRT beam position are held In counters, and the counter contents are converted to analog signals for driving the X-Y inputs to the CRT display.

except that the arithmetic units act as pass-throughs since the character generator has already computed

Ax and Ay. Also, switching circuits (not shown) can modify the arithmetic signs and interchange Ax and

Ay so the characters can be rotated.

The character generator is a conventional ROM- controlled algorithmic state machine that uses a look-up table to find the end points of short vectors for tracing each character. Scaling factors can be applied to the algorithms so the character size can be mag nified (xl, X2, x4, x 8). The Ax- Ay coordinate infor mation for each vector end point is sent to the vector generator.

Refresh Rate

The refresh rate depends upon the number of vec tors and characters to be drawn and the number of blanked movements of the CRT beam. Each normal- size character requires 15 /AS to trace. The vector trace time is according to the list on page 19 and the time for blanked movements is the same as for vector movements. As an example, consider a presentation that has 50 characters, a graticule of 21 vertical and 21 horizontal lines, 40 tick marks on the graticule, 60 blanked movements to trace the graticule and tick marks, 24 blanked movements to position the charac ters, and 200 data points joined by short vectors. Total trace time is then approximately:

50 characters at 15 ¿is

42 lines at 48 ¿us

40 tick marks at 4.5 ¿is

60 short blanked movements at 6 ¿is

24 blanked movements at 12 ¿is

200 data points at 1.5 ¿is

1/3894 ¿is = 250 Hz

= 750 ¿is

=2016 ¿is

= 180 ¿is

=360 ¿is

=288 ¿is

=300 ¿is

=3894 ¿is

Hence, the refresh rate for this data display is well above the flicker level.

Processing the Data

The data path from the input to the refresh memory is outlined in Fig. 6. ASCII-coded data written in the graphics translator machine language is accepted through the HP-IB interface in the following format:

N N xxxx,

yyyy; followed by a colon(:), carriage return (CR), or line feed (LF). The first two letters (NN) are a mnemonic for the instruction command (see Table I), and can be either upper or lower case. The parameters xxxx and yyyy are four-digit decimal numbers. For example, the instruction "pa 200, 500 moves the CRT beam to x = 200, y = 500 on the 1023 x 1024 matrix ("pa" is the mnemonic for "plot absolute"), xxxx and yyyy may not be used with some instruction commands.

The system is initialized when the decoder ROM

(see Fig. 6) detects CR, LF, or a colon(:). The instruc tion counter is then reset to 0, the system is put into the "listen program" mode, and the BCD data shift register is cleared. When the system is in this mode, the next two alphanumerics received through the in terface buffer are interpreted by the decoder ROM as an instruction. (If through some error these two al phanumerics are not one of the instruction com mands listed in Table I, the system goes into a "sleep" mode and does nothing until another CR, LF, or : is received.)

After the instruction counter counts the two al phanumerics, the system goes into th'e "listen data" mode and the numeric data is clocked into the BCD data shift register. When a parameter terminator ("," or " occurs, the register contents are converted to

2 0

© Copr. 1949-1998 Hewlett-Packard Co.

binary and transferred through the multiplexers to the register designated by the decoder ROM accord ing to the instruction command. When the next CR,

LF, or : is detected by the decoder ROM, the data is loaded into the next address in memory and a new instruction cycle is initiated.

An exception to the above occurs with the plot absolute (pa) command, which causes data to be loaded into memory each time a semicolon ( ap pears. This allows several coordinates to be transmit ted in one statement. For example, the single state ment "pa 100, 100; 350, 900; 600, 100; 100, 100 draws a triangle.

The instruction command "tx" causes the system to go into the text mode. The 7-bit ASCII code following tx is then loaded into the 10-bit Y coordinate register.

Character size and angle of rotation fill out the re maining three bits. The X coordinate register is filled with 1's and loaded into memory at the same time as the informmation in Y. During readout of the mem ory, the ten 1's in X indicate to the display circuits that the information in Y is to be sent to the character generator.

The system remains in the text mode until receipt of the end-of-text character (binary 3).

Each of the 32-bit words stored in the refresh mem ory contains the following:

X c o o r d i n a t e ( o r t e x t - m o d e c o d e ) 1 0 b i t s

First and Second

Alphanumerics

Registers

F i g . 6 . B l o c k d i a g r a m o f t h e d a t a p r o c e s s i n g c i r c u i t s .

21

© Copr. 1949-1998 Hewlett-Packard Co.

Vector

Memory

Address

fr-4

Vector

Memory

Address

PC=Pen Control

FBC=File

Blanking Control

Y coordinate (or ASCII character) 10 bits

F i l e n u m b e r 5 b i t s

M o n i t o r s e l e c t c o d e 4 b i t s

P e n c o n t r o l ( b l a n k o r u n b l a n k ) 1 b i t

F i l e b l a n k i n g c o n t r o l 1 b i t

U n a s s i g n e d 1 b i t

Pre-programmed Subroutines

To simplify the programming of the graphics trans lator, a number of graphics utility subroutines for use with several different host computers have been pre pared. The graphics command statements in the higher-level languages used with these programs were selected to be easy to understand and, if possi ble, to be already familiar to the user. For example, one of these routines, the 10184A Softcopy Graphics

Library designed to run on the Model 9825A Desktop

Computer, supports the Models 9862A and 9872A

Plotters as well as the graphics translator. This routine has graphics command statements and parameter meanings for the translator that for the most part are identical to the plotter command state ments. Hence, the user does not have to learn the graphics translator machine language (GTML).

The "hdcpy" statement in this subroutine indicates to the desktop computer that the data is to be sent to the plotter for a hard-copy output. Whenever the user gives a graphics command statement, the graphics subroutine first looks for the "hdcpy" flag. If the flag is clear, the system speaks GTML to the graphics translator via the HP-IB and the CRT display is up dated. If the flag is set, it speaks the HP graphics language (HPGL) to the plotter and the user obtains a hard copy of the graphics information.

RECEIVER AUDIO TEST

- I 8 7 - 1 0 7

R F L E V E L D B M

F i g . 7 . D i s p l a y r e s u l t i n g f r o m t h e p r o g r a m d e s c r i b e d i n t h e text. The bottom trace is the noise level at a receiver's output as a function of the RF input level. The middle trace is the level of the combined noise and distortion and the top trace is the signal plus noise and distortion.

Some of the Softcopy Graphics statements are: p i t x , y d r a w a l i n e t o x , y scl x1; x2, y1( y2 establish the scale range o f s t x , y o f f s e t t h e o r i g i n f i l e x d e s i g n a t e a f i l e n u m b e r b f i l e x , x , . . . b l a n k t h e s e f i l e s . v f i l e x , x , . . . . v i e w t h e s e f i l e s . fish x,y,y... flash this file (x) on these monitors (y,y,...]. m o n x , x , d i s p l a y s u b s e q u e n t d a t a o n these monitors. bmon x,y,...,y blank these files (y,y,...j from this monitor (x). vmon x,y,...,y view these files on this monitor.

Because the cartridge tape on which the Softcopy

Graphics Library is supplied, is written in the Model

9825A's machine language and includes the com piler, there is no need to use the "call" statement to execute the graphics command statements.

An example of a program written with Softcopy

Graphics statements is shown below followed by an explanation of the program steps. This program traces the display shown in Fig. 7, the result of a radio receiver test, and illustrates the relative simplicity of creating graphic displays with the Model 13 50 A using a Model 9825A Desktop Computer as a control ler and the Softcopy Graphics Library.

11 p c l r ; f x d 0 ; c s i z 3 s c l - 1 4 5 , - 2 0 , - 1 2 0 , 2 0 y a x - 1 2 7 , 1 0 , - 1 0 0 , 1 x a x - 1 0 0 , 2 0 , - 1 2 7 , - 2 6 p i t - 1 1 0 , 1 0 , 1 ; I b l " R E C E I V E R A U D I O T E S T " p i t - 9 0 , - 1 2 0 , 1 ; I b l " R F L E V E L D B M " f o r Y = - 9 0 t o 0 b y 1 0 p i t - 1 4 5 , Y - 2 , l ; i f Y > = 0 ; l b l " "

I b l Y , " D B " ; n e x t Y f o r X = - 1 2 7 t o - 2 5 b y 2 0 p i t X - 7 , - 1 1 0 , l ; l b l X ; n e x t X l  » D ; g s b " r e a d d a t a " i f F = l ; p l t X , Y , l ; l b l

2 * D ; q s b " r e a d d a t a "

3 * D ; g s b " r e a d d a t a " stp h d c p y l ; q t c 0 e n d i f F = l ; p l t X , Y ; j m p 0 i f F = l ; p l t X , Y , l ; l b l

" r e a d d a t a " :

' # " ; j m p 0

' * " ; j r o p 0

Explanation of the program:

L i n e 0 C l e a r s t h e p i c t u r e o n t h e C R T s c r e e n , sets the fixed point format, and estab lishes the size of characters to be used.

L i n e 1 E s t a b l i s h e s t h e u s e r ' s s c a l e r a n g e f o r the plotting area.

L i n e 2 D r a w s t h e Y - a x i s .

L i n e 3 D r a w s t h e X - a x i s .

Lines 4 & 5 Writes titles.

Lines 6-8 Writes labels on the Y-axis tick mark location.

Lines 9-10 Writes labels on the X-axis tick mark location.

Lines 11-13 Reads the DVM measured values and plots data. "F" is a flag that indicates another reading is to be taken. l-»-D,

2— »D, 3— »D set switches in the test set-

2 2

© Copr. 1949-1998 Hewlett-Packard Co.

Fig. 8. Graphics work station uses the Model 1350 'A Graphics

Translator with the Model 9825A Desktop Computer. Vectors a n d c h a r a c t e r s f o r a l l t h e d i s p l a y s s h o w n h e r e a r e s t o r e d i n

Model 1350A's files at the same time and directed to individual d i s p l a y s b y M o d e l 1 3 5 0 A ' s b l a n k i n g s i g n a l s .

up to supply the indicated inputs to the DVM.

Line 14 Stops the program execution.

Line 15 Sets hard copy flag and continues the program from line 0.

L i n e 1 7 B e g i n n i n g o f t h e s u b r o u t i n e t o m a k e measurements and to set F=0 if the measurement cycle is complete.

Acknowledgments

Tom Bohley and Bill Mason developed the vector generator. Bill also contributed to the character generator and the power supply. Mechanical design was by Bill Smith. Many thanks are also due Ed

Scholtzhauer of the Loveland Instrument Division

S P E C I F I C A T I O N S

H P M o d e l 1 3 5 0 A G r a p h i c s T r a n s l a t o r

I N P U T I N T E R F A C E : H P - I B l i s t e n e r o n l y t h a t c o n f o r m s t o I E E E 4 8 8 - 1 9 7 5 . D a t a acceptance rate is 2 /¿s per character.

X , Y , v e c t o r s , O U T P U T : - 0 . 2 V d c t o - 1 . 2 V d c i n t o 5 0 f l , X , Y , a n a l o g v e c t o r s , between addressable points. Positive up and to the nght.

2 A N A L O G O U T P U T : 0 t o 1 V u n b l a n k e d , - 1 V b l a n k e d , i n t o 5 0 . Q .

A D D R E S S A B L E R E S O L U T I O N : 1 0 0 0 x 1 0 0 0 p o i n t s .

MEMORY: 2048 Vectors or characters.

32 ADDRESSABLE FILES: may be of any length that does not exceed memory size. Files can be erased or blanked.

A D D R E S S A B L E W R I T E P O I N T E R : a l l o w s n e w d a t a t o b e w r i t t e n f r o m t h a t address forward.

C H A R A C T E R G E N E R A T O R : 8 x 1 2 r e s o l u t i o n s t r o k e c h a r a c t e r s . M o d i f i e d f u l l

ASCII set (compatible with HP 9825A keyboard). Character strokes are stored in plug-in ROM's.

4 P R O G R A M M A B L E S I Z E S : 1 x , 2 x , 4 x , 8 x , 8 0 c h a r a c t e r s p e r l i n e a n d 5 1 lines (not to exceed memory size) at 1 x character size.

2 PROGRAMMABLE ORIENTATIONS: 0° and 90°.

I N P U T C O N N E C T O R : r e a r p a n e l , c o n f o r m s t o I E E E 4 8 8 - 1 9 7 5 .

OUTPUT CONNECTORS: three rear panel BNC's for X, Y, and Z axes with shields grounded. Four rear panel BNC auxiliary outputs for TTL blanking of displays.

FRONT PANEL INDICATOR LIGHTS: power interrupt, listen data, listen program, power on.

OPERATING ENVIRONMENT

TEMPERATURE: (operating) 0°C to +55=C (+32°F to +130°F); (non-operat ing) -40°C to +70°C (-40°F to + 158°F).

HUMIDITY: to 95% relative humidity at +40=C ( + 104°F).

A L T I T U D E : ( o p e r a t i n g ) t o 4 6 0 0 m ( 1 5 0 0 0 f t ) ; ( n o n - o p e r a t i n g ) t o 7 6 0 0 m

(25 000 ft).

SHOCK: 30 g level with 1 1 ms duration and 1/2 sine wave shape.

VIBRATION: vibrated in three planes for 15 min. each with 0.25 mm (0.010 in) excursion, 10 to 55 Hz.

P O W E R : s e l e c t a b l e 1 0 0 , 1 2 0 , 2 2 0 o r 2 4 0 V a c , + 5 % , - 1 0 % , 4 8 H z t o 4 4 0 H z m a x i m u m p o w e r 1 0 0 V A a p p r o x i m a t e l y 8 0 W ) . A v e r a g e p o w e r d i s s i p a t i o n a t

60 Hz and 120 V without any options is approximately 74W.

S I Z E : 9 8 m m H x 4 2 6 m m W x 5 1 1 m m D ( 3 . 8 7 5 x 1 8 . 9 3 7 x 2 0 . 1 2 5 i n ) .

WEIGHT: 4.5 kg (2 Ib).

PRICE IN U.S.A.: Model 1350A Graphics Translator, $3450.

M A N U F A C T U R I N G D I V I S I O N : C O L O R A D O S P R I N G S D I V I S I O N

1900 Garden of the Gods Road

P . O . B o x 2 1 9 7

Colorado Spring, Colorado 80901 U.S.A. who provided much help in the development of the

Softcopy Graphics Library, and to new-product plan ning managers Dave Wilson and Bob Bell who helped

define the instrument. &

K u n i o H a s e b e

K u n i o H a s e b e j o i n e d H P ' s i n t e r continental operations in 1 973 as a s t a f f e n g i n e e r , a p o s i t i o n t h a t i n v o l v e d a c o n s i d e r a b l e a m o u n t o f t r a v e l i n t h e f a r e a s t . H e l a t e r b e came the intercontinental specialist on the HP interface bus, logic analysis, and digital signal analysis. Wishing to get involved in

R and D, Kunio transferred to the

1,1 Colorado Springs Division in 1 976, f ' J w h e r e h e d i d s o m e o f t h e p r o g r a m m i n g a n d I / O d e s i g n f o r t h e r i 1350A Graphics Translator. Kunio m J m w a s b o r n i n J a p a n b u t w h e n h e w a s 1 3 h i s f a m i l y m o v e d t o H a w a i i . T h e r e , h e o b t a i n e d b o t h

BSEE and MSEE degrees from the University of Hawaii in 1971 a n d 1 9 7 2 . F o n d o f d r i v i n g , K u n i o l i k e s t o u n w i n d b y w i n d i n g a r o u n d C o l o r a d o ' s m o u n t a i n r o a d s i n h i s a g i n g B M W .

A r n o t L . E l l s w o r t h

Fresh out of the U.S. Navy, Arnie

Ellsworth joined HP's Colorado

Springs Division In 1969 as a f f production-line technician. He also started engineering studies part-time at the University of Col orado. In 1972, he transferred to t h e R a n d D l a b s , e v e n t u a l l y a s suming project leadership of the

1317A and 1321 A CRT displays b e f o r e b e c o m i n g p r o j e c t l e a d e r on the 1350A. Arnie earned his

B S E E d e g r e e a t U C i n 1 9 7 4 a n d his ME degree in 1977. Work and school has left little spare time but weekends are devoted to his family (wife, boy 5, girl 7) and church work. Arnie's a Corvette buff and he also joins his daugh ter in learning stunt roller skating.

2 3

© Copr. 1949-1998 Hewlett-Packard Co.

Laboratory Notebook

Swept-Frequency Measurements of High

Levels of Attenuation at Microwave Frequencies

A major difficulty facing anyone measuring high attenuation levels at microwave frequencies is getting adequate power to the measuring instrument's detector. One way around this problem is provided by the setup shown in the diagram.

Microwave power from the sweep oscillator is split off through a series of couplers and supplied directly to the measuring instru ment's detector. The remaining power passes through a microwave amplifier and an amplitude modulator then through the attenuator under test before being coupled to the direct power path prior to detection.

The path containing the attenuator under test was made many wavelengths longer than the direct path so while the frequency is swept, the microwave power from the two paths at the detector goes rapidly in and out of phase. The resulting display on the CRT of the frequency response test set is thus a closely-spaced series of peaks, as shown in the photo, with the envelope of the peaks delineating the attenuation-vs-frequency characteristics of the attenuator under test.

The advantage of this setup is that the power in the direct path causes the detector to operate as a linear detector, as long as the signal from the attenuator path is much smaller than the direct path. This greater measurement sensitivity is thus obtained. This system, which is used for production-line testing of the Model

8496B/H Step Attenuators, has a dynamic range of 120 dB.

Much helpful advice was provided by Bob Kirkpatrick in the design of this system.

Robert /acobsen

Stanford Park Division

" S e e " E c o n o m i c a l P r e c i s i o n S t e p A t t e n u a t o r s f o r R F a n d M i c r o w a v e s , " b y G . R . K i r k p a t r i c k a n d D . R .

V e t e r a n , H e w l e t t - P a c k a r d J o u r n a l , M a y 1 9 7 4 .

Leveling

Frequency

Response

Test Set

30-kHz

Square Wave

10-dB

1 8 G H z

3-dB

Sweep

Ramp

Sweep

Oscillator

20-dB

Microwave

Amplifier

Attenuator

Under Test

H e w l e t t - P a c k a r d C o m p a n y , 1 5 0 1 P a g e M i l l

Road, Palo Alto, California 94304

Bulk Rate

U.S. Postage

Paid

Hewlett-Packard

C o m p a n y

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Hewlett-Packard Company

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