Tektronix TM 500 FG 502 function generator Instruction manual

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| INSTR
| Tektronix, Inc.
Ш Р.О. Вох 500
Beaverton, Oregon 97005 . Serial Number
070-1706-00 1073
EE Contents of this publication may not be reproduced in any
form without permission of Tektronix, inc.
Е U s. A: and Foreign TEKTRONIX products covered byt US,
uu | and foreign patents and/or patents pending.
i Ye KTRONIX à registered trademark 0 of Tektronix, ne. ая ; ны ая | о
Peet
SECTION 1
SECTION 2
SECTION 3
FG 502
TABLE
OF CONTENTS
OPERATING INSTRUCTIONS
Instrument Description
Preparation For Use
Initial Operation
Functions Available At Rear Connector
Operating Considerations
Qutput Connections
Risetime and Falitime
Impedance Matching
Operation
Free-Running Output
Gated Output
Voltage-Controlled Frequency (VCF) Output
Applications
Response Analysis
Tone-Burst Generation or Stepped Frequency Muitiplication
Electrical Characteristics
THEORY OF OPERATION
Introduction
Triangle Generator
Sine Shaper
Sine Wave Buffer
Output Amplifier
Power Suppiies
SERVICE INFORMATION
Symbols and Reference Designators
Rear Interface Connector Assignments
Electrical Parts List
Internal Adjustment Procedure
Services Available
Maintenance
Test Equipment
General
Parts Location Grid
Front Panel Controls and Connectors
Biock Diagram
Triangle Generator Schematic
Sine Shaper & Buffer Schematic
Output Amplifier and Switch Details Schematic
Power Supply Schematic
Mechanical Parts List
Exploded View
Accessories and Repackaging
CHANGE INFORMATION
o
Page
1-1
1-1
1-1
1-1
1-2
1-2
1-2
2-1
2-1
2-2
2-2
2-2
2-2
3-1
3-2
3-3
FG 502 a
The FG 502 Function Generator is designed to operate
in a TM 500 series power module. Low distortion sine,
square, triangie, positive and negative puise and ramp
waveforms from 0.1 Hz to 11 MHz, are available at the
front panel. À +2.5 V square wave trigger also is available at
the front panel. Variable DC offset of +5 V is also provided.
A voltage-controlled frequency (VCF) input controls the
output frequency from an external voltage source, The
output frequency can be swept above or below the selected
frequency, to a maximum of 1000.1, depending on the
polarity and amplitude of the VCF input and the selected
output frequency,
Also included is an external gate input that allows the
generator to operate for the duration of an externally
Section 1-FG 502
OPERATING
STRUCTIONS
applied gating signal. This mode provides either a single
cycle output, or a train {burst} of preselected waveforms,
depending on the gating signal width and the generator
frequency setting,
The variety of swept and modulated signals available
from the FG 502 make it especially useful for such
applications as testing servo-system or amplifier response,
distortion and stability, lt is also useful for FM generation,
frequency multiplication, or as a variable beat-frequency
oscillator, repetition-rate, or tone-burst generator. The
square wave trigger output can be used as a source for TTL
logic, or to synchronize an external device such as an
oscilloscope or counter,
PREPARATION FOR USE
Initial Operation
caution |
Turn the Power Module off before inserting the plug-
in; otherwise, damage may occur to the plug-in
circuitry.
The FG 502 is calibrated and ready for use when
received, It is designed to operate in any compartment of
the TM B00 series power module. Refer to the power
module instruction manual for line voltage requirements
and power module operation, See Fig. 1-1 for instailation-
removal procedure. Check that the FG 502 is fully inserted
in the power module, Pull the PWR switch on the power
module, Check that the green POWER light on the FG 502
REV. 8B, MAY, 1975
is on. The Controls, Connectors and Adjustments foldout
page In Section 3 gives a complete description of the front
panel controls and connectors,
Functions Available At Rear Connector
Refer to the rear connector assignment illustration in the
Service Section of this manual for pin assignments.
A slot between pins 23 and 24 on the rear connector
identifies the FG 502 as a member of the signal source
family. A barrier may be inserted in the corresponding
position of the power module jack, to prevent other than
signal source plug-ins from being used in that compartment.
This protects the plug-in should specialized connections be
made to that compartment. Consult the Building A System
section of the power module manual for further
information.
1-1
Operating Instructions—FG 502
POWER
MODULE
Barrier
Top
Groove
Bottom
Groove
Fig. 1-1. FG 502 Installation and removal,
OPERATING CONSIDERATIONS
Output Connections
The output of the FG B02 is designed to operate as a
50 {2 voltage source working into a 50 {1 load. At the higher
frequencies, an unterminated or improperly terminated
output will cause excessive aberrations on the output
waveform (see impedance Matching discussion). Loads less
than 50 {1 will reduce the waveform amplitude.
Excessive distortion or aberrations, due to improper
termination, are less likely to occur at the lower frequencies
{especially with sine and triangle waveforms}. To ensure
waveform purity, observe the following precautions:
1. Use good quality 50 £2 coaxial cables and connectors.
2. Маке all connections tight and as short as possible.
3. Use good quality attenuators, if necessary to reduce
waveform amplitude to sensitive circuits,
1-2
4. Use terminators or impedance-matching devices to
avoid reflections when using long cables {6 feet or more}.
5. Ensure that attenuators, terminations, etc. have
adequate power handling capabilities for the output wave-
form,
Risetime and Falltime
if the output pulse from the FG 502 is used to measure
the rise or falltime of a device, consider the risetime
Characteristics of the associated equipment used. 1f the
risetime of the device under test is at {east 10 times greater
than the combined risetimes of the FG 502 plus the
monitoring oscilloscope and associated cables, the error
introduced will not exceed 1%. This error can generally be
ignored. When the rise or falitime of the test device is less
than 10 times as long as the combined risetimes of the
testing system, the actual risetime of the device must be
determined. This is found from the risetime of each
component making up the system. The total risetime equals
a
the square root of the sum of the squares of the individual
risetimes. Ry = (Ry) + (Ro) + (Ry) +... Conversely,
the risetime of the device under test can be found, from the
same relationship, if the actual risetimes in the system are
known.
The physical and electrical characteristics of the pulse
transmitting cable determine the characteristic impedance,
velocity of propagation, and amount of signal loss. Signal
loss, is related to the frequency: therefore, a few feet of
cable can attenuate high frequency information in a
fast-rise puise. it is important therefore, to keep these
cables as short as possibie.
When signal comparison measurements or time differ-
ence determinations are made, the two signals from the test
device should travel through coaxial cables with identical
joss and time delay characteristics,
If there is a DC voltage across the output load, the
output pulse amplitude will be compressed, or in some
cases (if the voltage exceeds £10 V}, it may short the
output. To prevent this from occurring, the output must be
coupled through a DC blocking capacitor to the load. The
time constant of the coupling capacitor and load must be
long enough to maintain pulse flatness,
impedance Matching
As a pulse travels down a tranmission line, each time it
encounters a mismatch, or different impedance than that of
the transmission line, a reflection is generated and sent back
along the line to the source. The ampiitude and polarity of
the refiections are determined by the amount of the
encountered impedance in relation to the characteristic
impedance of the cable. If the mismatch impedance is
higher than the line, the reflection will be of the same
polarity as the applied signal. If it is lower, the reflection
will be of opposite polarity. |
if the reflected signal returns before the pulse is ended,
it adds to or subtracts from the amplitude of the pulse. This
distorts the pulse shape and amplitude, 1f the FG 502 1s
driving a high impedance such as the 1 M& input imped-
ance (paralieled by a stated capacitance} of the vertical
input to an oscilloscope, connect the transmission fine to a
50 © attenuator, 50 © termination, and then the oscillo-
scope input. The attenuator isolates the input capacitance
of the device, and the FG 502 is properly terminated.
A simple resistive impedance-matching network, that
provides minimum attenuation, is illustrated in Fig. 1-2. To
match impedance with the lllustrated network, the То!
lowlng conditions must exist:
(Ry +Zo) Ro
rada. ——E E MUST eQUAÍ Z
В + 25 + В, QUE 64
Operating Instructions—FG 502
and
Ry + Z,+R must equal Za.
Therefore:
or
and .
La — La:
For example, to match a 50 © system to a 1250
system, Zy equals 50 (2 and Z, equals 125 ©).
| Therefore:
В, =,/125{125 — 50) = 96.8 ohms
L
and |
В, = 50V2- - 64.6 ohms.
126-50
E E
z, A Ry 2,
— (O % di
(Low) © y {High}
Ro
ev
2, < 2.
Fig, 1-2. impedance matching network that provides minimum
attenuation,
1-3
Operating Instructions—FG 502
When constructing such a device, the environment
surrounding the components should be designed to provide
a transition between the impedances. The characteristic
impedance of a coaxial device is determined by the ratio
between the outside diameter of the inner conductor to the
inside diameter of the outer conductor
(Zo = 13810910 D/d)
JE
1) is the inside diameter of the outer conductor, d is the
diameter of the inner conductor, and © is the dielectric
constant {1 in air}.
The network in Fig. 1-2 provides minimum attenuation
for a purely resistive impedance-matching device. The
attenuation as seen from one end does not equal that seen
from the other end. A signal (E4} applied from the lower
impedance source encounters a voltage attenuation (Ay)
that is greater than 1 and less than 2, as follows:
A signal (E,) applied from the higher impedance source
{Z,) encounters a greater voltage attenuation {A,) that is
greater than 1 and less than 2(Z,/Z2,):
Ag = Ez = Ry + В,
= + 1
1 № A
In the example of matching 50 © 10 125 ©,
96.8
and
96.8 96.8
The illustrated network can be modified, to provide
different attenuation ratios, by adding another resistor {less
than R4) between Z4 and the junction of R, and Ro.
OPERATION
Free-Running Output
Set the AMPLITUDE control fuliy clackwise, and make
certain the OFFSET contro! is pushed in. Set the FUNC-
TION selector to the desired waveform. See Fig. 1-3. Select
the desired frequency with the MULTIPLIER and
FREQUENCY Hz dials. Note the ramp and pulse fre-
guencies are one-tenth the FREQUENCY Hz and MULTI-
PLIER diaí settings. The output frequency is calibrated
when the FREQUENCY VERNIER control is in the full
clockwise position. Connect the load to the OUTPUT
connector and adjust the AMPLITUDE control for the
desired output amplitude. Pull and adjust the OFFSET
control to position the DC level (baseline) of the output
waveform above or below OV as desired.
Fig. 1-3. Output waveforms avatlable from the FG 502,
1-4
Gated Output
A gating signal of at least O V to +2 V applied to the
GATE IN connector provides gated waveforms. The dura-
tion of the output waveforms depends upon the duration of
the gating signal, The number of cycles during the burst
depends upon the FREQUENCY Hz and MULTIPLIER dial
settings. Single cycles can be obtained by applying a gating
signal with a period approximately egual to the period of
the FG 502 output. The number of cycles per burst may be
approximated by dividing the gating signal duration by the
period of the FG 502 output,
Output frequency can be varied during the burst
duration by applying the proper voltage to the VCF IN
connector. See Voltage-Controiled Frequency (VCF) Out-
put following.
Voltage-Controlled Frequency (VCF) Output
The output frequency of the FG 502 can be swept over
a frequency range of 1000:1, depending on the MULTI
REV. B, NOV. 1974
Operating Instructions FG 502
PLIER setting, by applying a 0 V to 10 Y signal to the VCF To
IN connector, It may be necessary to vary the CAL control 11 ВЕ > мн
to obtain the full 1000:1 swept range or the fowest swept 105 - - z
frequency desired, See Fig. 1-4 for maximum VCF range Ë 105. 1.1 kHz 1.1 MHz
for each MULTIPLIER setting. =
| Daga. 110 Hz 110 kHz
==
The polarity of the VCF input signal determines the 5 103. 11 Hz 11 kHz
direction the output frequency is swept from the frequency e
set by the MULTIPLIER, FREQUENCY Hz, and = 107; 19 Hz 1.1kHz
VERNIER controls. A positive-going voltage raises the E 407. 6.11 Hz 110 Hz
frequency, while a negative-going voltage lowers the fre- =
quency, A voltage that varies symmetrically about OV & 4 1011Hz 11 Hz
sweeps the output frequency symmetricaily about the 011Hz 11H
center frequency determined by the frequency controls. 10 — 7
See Fig, 1-5. | | : ' ' J
9 1071 1 101 10% 19% 40% 195 10° 10’
; , ; . F
Since the VCF Input amplitude versus frequency is a requeney Ez
linear relationship, the frequency output range may be
determined from the VCF input amplitude, Refer to the |
Fig. 1-4. Graph showing range of frequencies for each MULTIPLIER
following test under the heading Response Analysis for a setting that can be swept with a 0 to 10 Y signal applied to the VCF
typical! application using the VCF feature. input,
SWEPT FREQUENCY
RANGE
{A} {B} {C}
+5
VCFIN O
5
OUTPUT OUTPUT OUTPUT
Fig. 1-5. Swept Frequency range with 10 V signals applied to VCF IN Connector.
REV. B, APR. 1976 1-5
Operating Instructions—FG 502
APPLICATIONS
Response Analysis
The FG 502 is particularly suited for determining
response characteristics of circuits or systems, This applica-
tion utilizes the VCF input of the FG 502 to sweep the
generator over a range of frequencies. By applying the
desired waveform from the FG 502 to a device under test,
and sweeping the waveform frequency over a selected
range, various response characteristics can be observed on a
monitoring oscilloscope.
The following procedure describes a technique for
determining response characteristics of any frequency
sensitive device that operates within the frequency range of
the FG 502. Refer to the Voitage-Controiled Frequency
(VCF) Output discussion under Operation for additional
information.
1. Connect the equipment as shown in Fig. 1-6.
2. Set the MULTIPLIER selector and FREQUENCY Hz
dial for the desired upper or lower frequency limit
{depending on the direction you wish to sweep), See Fig.
1-4 for VCF ranges and MULTIPLIER settings.
the desired waveform to the VCF IN
4. Adjust the amplitude of the VCF input waveform for
the desired output frequency range.
5. Observe the response characteristics on the mon-
itoring oscilloscope.
The frequency at which a displayed response char-
acterístic occurs can be determined by first removing the
VCF input waveform, then manually adjusting the FRE.
QUENCY Hz dial to again obtain the particular characteris-
tic observed in the swept display. Then read the frequency
on the FREQUENCY Hz dial,
Tone-Burst Generation or Stepped Frequency
Multiplication
The FG 502 can be used as a tone-burst generator or
frequency multiplier for checking tone-controlled devices.
This application utilizes a Pulse Generator, such as the
Tektronix PG 501, as a gating signal source and a Ramp
Generator, such as the Tektronix RG B01, as a VCF signal
source.
The following procedure describes a technique for
obtaining a tone-burst or frequency multiplied output from
the FG 502. Refer to the Gated (Burst) Output and the
3. Apply Voltage-Controlled Frequency (VCF) Qutput discussions
connector, under Operation for additional information.
WAVEFORM
GEN OSCH.LOSCOPE
VCE de
IN OUTPUT 7 O
0 0 O
DEVICE
UNDER
TEST
Fig. 1-6. Analyzing circuit or system response.
1-6 e
REV, APR 1974
1. Connect the equipment as shown in Fig. 1-7.
2. Set the Ramp Generator for the desired ramp
duration and polarity.
3. Adjust the Pulse Generator period for the desired
number of bursts within the selected ramp duration.
Adjust the Pulse Generator duration for the desired burst
width.
Operating Instructions--FG 502
4, Select the sweep frequency range by adjusting the
FREQUENCY Hz dial for one end of the swept range
{upper or lower limit depending on the polarity of the
ramp}. Then adjust the Ramp Generator amplitude for the
other swept frequency limit.
Various other tone-burst or frequency multiplied char-
acteristics can be obtained by using different gating input
waveforms, i.e. triangle, sine, square, etc,
VCF IN*
GATE IN*
Tone-Burst or
Stepped Frequency
Output
GEN
EXT =
IN e.
OUT [7
DEVICE
BNC T
UNDER
TEST
Fig. 1-7. Tone burst generation or stepped frequency multiplication,
ELECTRICAL CHARACTERISTICS
Performance Conditions
The electrical characteristics are valid only if the FG 502
is calibrated at an ambient temperature between +20°C and
+30°C, and operated between O°C and +50°C, uniess
otherwise noted,
WAVEFORMS:
Sine, triangle, square, ramp and pulse,
FREQUENCY RANGE:
0.1 Hz to 11 MHz.
FREQUENCY RESOLUTION:
1 part in 10% of fuit scale setting using the FRE.
QUENCY VERNIER control.
1-7
ET REV. APR 1974
Operating Instructions—FG 502
FREQUENCY STABILITY:
<0.1% for 1 hour, <0.5% for 24 hours. Dial must be on
calibrated portion and ambient temperature must be
25°C +5°C.
PULSE AND RAMP FREQUENCY:
1/10 triangle frequency,
DIAL RANGE:
1 to 11 calibrated, 0.7 to 1 uncalibrated,
DIAL ACCURACY:
3% of full scale from 0.1 Hz to 1 MHz,
<b% of fuil scale from 1 MHz to 10 MHz.
11 MHz setting not less than 11 MHz.
AMPLITUDE:
10 V P-P open circuit, 5 V P-P into a 50 © load,
excluding offset, referenced at 10 kHz.
AMPLITUDE FLATNESS:
Sine Wave: < 11.5 dB referenced at 10 kHz.
Square and triangle to sinewave amplitude < +3 db.
OFFSET RANGE:
+5 V open circuit, +2.5 V into a 50 £2 load.
SINE WAVE DISTORTION:
Equal to or less than 0.5% from 10 Hz to 50 kHz.
Harmonics > —30 dB down at all other frequencies.
Dial must be on calibrated portion, and ambient temper-
ature must be 25°C £5°C,
TRIANGLE SYMMETRY:
Within 1% from 0.1 Hz to 1.1 MHz, within 3% from
1.1 MHz to 11 MHz using 10° MULTIPLIER setting.
1-8
Dial must be on calibrated portion. Ambient temperature
must be 25°C 45" C,
TRIANGLE LINEARITY:
Within 1.0% from 0.1 Hz to 110 kHz, within 3% from
100 kHz to 1.1 MHz using 10° MULTIPLIER setting,
within 5% from 1 MHz to 11 MHz using 10% MULTI-
PLIER setting.
SQUARE WAVE and PULSE OUTPUT:
Risetime: =20 ns,
Aberrations:=3% P-P at full amplitude into a 50 47 load.
PULSE AND RAMP ASPECT RATIO:
95/5,
VOLTAGE CONTROLLED FREQUENCY INPUT:
Range: A 10 V signal shifts frequency = 1000:1 where
maximum frequency <11X MULTIPLIER setting and
minimum frequency 20.011X MULTIPLIER setting. 7 |
Siew Rate: 20.5 V/us,
EXTERNAL GATE INPUT:
O V to 2+2 V, not to exceed +15 V. Baseline of output
waveform during off period within 500 mV measured
from О М. input impedance is 1 k{l. Usable on the 10°
MULTIPLIER setting only for sine, triangle, or square
waveform outputs.
TRIGGER QUTPUT:
+2.5 V from 50 ©.
POWER CONSUMPTION:
15 watts,
REY, E, JAN. 1976
introduction
The triangle waveform is the basic waveform in the
FG 502. The ramp waveforms are triangle waveforms with
non-equal runup and rundown times. The sine wave is
derived from the triangle waveform, using a four step
approximation. The square and pulse waveforms are
generated by the triangle generator control circuitry.
Refer to the simplified Block Diagram, and the circuit
diagrams in the pullout pages of this manual along with the
following discussion, for a complete understanding of the
FG 507 operation.
Triangle Generator
Operational amplifier U140, with Q140, and the positive
timing resistors, form a positive constant current source,
U175, 0175, and the negative timing resistors form a
negative constant current source. These constant current
sources supply the current (either positive or negative} to
charge the timing capacitor, generating the triangle
waveform,
To understand the operation of this circuit, assume the
junction of CR140 and CR170 is positive with respect to
ground. CR140 is off and CR170 is conducting. CR175 is
off, and the capacitor is charging from the positive current
source through CR145. 0292 is off, clamping the junction
of CR140 and CR170 at approximately 5 V above ground.
This action occurs through CR300, CR304, CR308 and
CR312, Current to hold the junction of CR140 and CR170
positive is supplied via R155, connected to the +17 V
supply.
in this state CR248 is on, CR245 is off, and the voltage
level at the base of Q232 {not conducting) is set by the
current flowing through R245, CR2486, and R240,
The ramp, moving in the positive direction, appears in
the same polarity at the base of Q230B, This is accom-
plished through the action of source follower Q220, with
its constant current source 0202. 0204 and Q210, com-
plementary emitter followers, drive the AC compensated
attenuator R1224, C224, and R220.
® REV. APR 1974
Section 2—FG 502
THEORY
OF OPERATION
When the base of 02308 (now conducting) reaches the
same voltage as the base of Q230A (Q230A and 02308
form a comparator) O230B stops conduction and QZ30A
turns on, The collector of O230A goes positive, turning
Q292 on and Q290 off. The collector of Q292 goes negative,
limited to about —5 V by diodes CR302, CR306, CR310
and CR314, This action turns diodes CR248 and CR246 off,
setting the leve] at the base of 0232 slightly below ground.
The negative voltage at the junction of CR140 and CR170
turns CR175 on and CR170 and CR145 off. This action dis-
connects the positive current source from the timing capac-
itor and connects the negative current source through
CR175, causing the ramp to go in the negative direction.
The action continues until Q230B turns on, by the negative
ramp at its base, and the entire cycle is repeated. R250 sets
the voltage at the base of Q230A and therefore, the DC
level of the triangle waveform.
The frequency of the triangle waveform is controlled by
two factors: (1) the value of the timing capacitor, and (2)
the amount of current available to charge ¡t. The current is
varied by changing the value of the timing resistors, (the
larger the value of the timing resistors and capacitors, the
slower the rate of rise), and the voltage across the timing
resistors, |
The voltage across the timing resistors is essentialiy the
voltage at pin 3 of operational amplifiers U140, in the
positive current source, and U175, controlling the negative
current source. The voltage at pin 3 of U140 is controlled
by summing amplifier U135. The voltage at pin 3 of U175
is controlled by summing amplifier U170. Input voltage to
these summing amplifiers is controlled by the
FREQUENCY Hz dial through U100, or the voitage present
at the VCF IN front panel connector, When the voltage at
pin 3 of U100 goes more positive by increasing the
FREQUENCY Hz dial setting, or through the VCF IN
input, the voltage at pin 6 of U140 goes negative, and pin 6
of 175 positive. This action increases the voltage across
the timing resistors. The value of the timing resistors and
timing capacitor is selected by the front panel
MULTIPLIER switch, R170 improves low frequency
symmetry by compensating for bias currents in the
operational amplifiers when operating at low voltage levels.
Voltage levels through this circuit are 0 to about +10 V at
the input of U100. This is translated at about +7 V to +17 V
at pin § of U135.
2-1
Theory Of Operation—FG 502
During non-gated operation, the base of Q332 is two
diode drops above ground. 0332 is off and Q330 is
conducting. 0325 is. on and Q315 off, back biasing CR315,
and allowing normal operation of the triangle generator,
When the proper level gating signal is applied to the front
panel GATE IN connector, the base of 0332 alternates
with the gating signal. When the gating signal is low (ground
potential} Q332 conducts. This action translates to con-
duction in Q315 and forward biasing CR315b. This locks the
junction of CR140 and CR170 at the level set by R155,
causing these diodes to conduct the timing capacitor
charging current to ground, through Q315, Operation of
the triangle generator is inhibited by this action. When the
gating signal goes positive CR315 is back biased, and the
generator functions normally.
Ramp waveforms are generated by changing the value of
either the positive or negative timing resistor, to create
different rise and fail times.
The square wave that controls charging of the timing
capacitor is picked off at the collector of Q290, to operate
the trigger out amplifier. The impedance looking into the
emitter of Q268 is about 51 2. The same waveform
operates the isolation diode bridge CR260, CR262, CR264,
and CR266. The output from this bridge is the square or
pulse waveforms. The triangle waveform, to the output
amplifier and sine shaper, is taken from the emitter of
©0210.
Sine Shaper
This circuitry provides a four step approximation of a
sine wave, from the triangle waveform, by use of a diode
ladder configuration. This circuit consists of four bridges.
All inputs to these bridges are connected to R350, and all
outputs are connected to their common load resistor R395.
Each bridge is supplied by current from the +17 V and
—17 Y supplies through different value resistors, R358,
R368, R378, R388 and their equal value complementary
resistors in the negative supply leads.
As the triangle waveform increases in voltage, each
bridge reaches a current limit whereby it can no longer
increase current through the load resistor, R395. These
current limits are set by R382, R384, R388, and similar re-
sistances for the other bridges. R350, and R250 are set for
minimum sine wave distortion. @
Sine Wave Buffer
This circuit operates as an inverting operational
amplifier, with a gain of about three or four. The sine wave
output from the shaper is fed to the base of Q400. A
negative-going signal at the base of 0400 causes ¡ts collector
2-2
REV. APR 1974
to go positive and the collector of Q410 negative, The
collectors of Q420 and Q430 respond in the opposite
polarity. 0440 inverts the waveform at the collector о?
0420, and the bases of Q442 and 0444 are driven in the
same polarity. Output and negative feedback are taken
from the junctions of R442 and R444. R450 in the
negative feedback loop sets the DC gain, and C450 sets the
AC gain.
Output Amplifier
This circuit operates as an inverting operational
amplifier. The selected waveform is applied to the base of
Q480 through the AMPLITUDE control, R465. 0480 and
0490 operate as an emitter-coupied amplifier. The collector
of Q480 drives the base of Q500. The base of Q515 is
driven by the collector of O500, The coliector of Q490
drives the base of (1506. The polarities are such that the
collectors of 0515 and O506 move in phase, Their
collectors drive the parallel output stage Q530, 0532,
0540, and Q542. The bypassed resistors in the emitter
circuit of the output transistors limit the output current.
R550, R552, R555, and R556 provide a back termination
of 5012, Negative feedback is taken from the junction of
the current limiting resistors in the output stage. R506, in
the feedback loop, sets the DC gain while C564, C5606,
C568, and CB74 adjust the AC gain. R475, the OFFSET
control, places an adjustable DC bias on the input of the
amplifier,
Power Supplies
The diode bridge, CRGOO, rectifies 25 V AC from the
power module. The full wave rectified DC is filtered by
C602 and applied as regulated +20 V DC to the circuitry in
the FG 502, through the series pass transistor located in the
power module.
VROIO sets the voltage at pin3 (+ Input of an
operational amplifier} of U615. U615 has a gain of
approximately three. The output at pin 6 therefore, is
about 20 V. Emitter follower Q620 drives the base of the
series pass transistor. Should the +20 V load increase, pin 2
of UGI5 (through R623 and R625) goes negative. This
causes pin 6 to go positive, increasing current flow and
restoring the +20 V to its previous level, Should the current
drawn increase, so the voltage across R632 is sufficient to
tum 0622 on, current limiting occurs, Q620 reduces
conduction, reducing the current through the series pass
transistor to a safe level. CRB32 protects the +20 V supply,
should it short to the minus supply.
U664 is an operational amplifier with a gain of about
one. The reference voltage is the +20 V applied at pin 2.
The output at pin 6 {—20 V} drives emitter follower 0662,
0662 drives the series pass transistor located in the power
module, Current limiting takes place in conjunction with
E
Q660 and R655. Feedback occurs through R678. The
action of this circuit is similar to the +20 V regulator.
CR655 protects this supply, should a short occur to +20 V.
The +17 V is referenced to the +20 V. U635, with a gain
of about one, controls Q635, the series pass transistor for
this supply. Feedback occurs at pin 2 of US35. Current
limiting in the +20 V supply protects this circuit.
Theory Of Operation—FG 502
The —17 V supply is referenced to the +17 V at pin 2 of
U650. The gain of UG50 is about one. Q650 serves as the
series pass transistor for this supply. Feedback occurs
through R640. Current limit for this supply is the +20 V
supply.
The regulatory action of the +17 V and —17 V supplies is
similar to that in the 20 V supplies.
FG 502
Electrical components shown on the diagrams are in the following units uniess noted otherwise:
Capacitors = Values one of greater are in picofarads (pF).
Values less than one are in microfarads {uF},
Resistors = Ohms (£2)
Symbols used on the diagrams are based on ANS! Y 32.2 — 1970.
Logic symbology Is based on MIL-STD-800B in terms of positive logic. Logic symb">