Signal Stability Analyzer
Now with Close-in Phase Noise personality
Signal Stability
50kHz to 65MHz
Real Time Phase and Fractional Frequency Data View
Time (Allan variance) and Frequency Domain (FFT) Analysis
Data Storage
Analogue Meter
Signal Stability Analyzer
Absolute Frequency
Flexible & Easy to Use
Statistics: Max • Min • Mean • Standard Deviation
Fractional Frequency Difference
roadband 50kHz – 65MHz input with
high resolution 5 or 10MHz input
• Large digital display of phase / relative
& absolute frequency
• Block storage of data files enables
offline analysis
• RS232 & USB connect to PC
• 32,768 data point storage
• Crash proof with 24Vdc Battery Back Up
• On screen Allan variance and phase
noise plots in real time
• Measurement error fully specified
• Plot print and save functions
Phase Difference fs • ps • ns • µs • ms • s
• Industry Best Phase Stability & lowest
• Very high resolution: <50fs single shot
(5 and 10MHz)
• Very low noise: 1s <5x10-14
• Ultra fast measurement time
• Sample rate: up to 1000 readings/second
• Selectable filters, resolutions & tau's
• Phase/frequency analogue meter
extremely useful and simple to use
Applications from Metrology
to Production Test
The A7-MX is the latest substantially
enhanced successor to Quartzlock’s long line
of phase/frequency comparators.
The A7-MX is invaluable in the design of low noise oscillators, atomic frequency
standards and passive devices where close in phase noise, freedom from spurii,
and phase stability are essential design objectives.
The A7-MX is unique in its ability to measure time domain stability at averaging
times from 1ms to weeks, and phase noise from mHz to 500Hz. Discrete spurii
can be measured close to the carrier at levels down to -120dBc.
The high resolution input operates at 5 or 10MHz. The reference is also at 5 or
A lower resolution input is provided which will measure at frequencies between
50kHz and 65MHz.
The A7-MX is not limited to research and development. The real time digital
display of fractional frequency offset combined with the high resolution analogue
meter makes the production setting of all types of frequency standard a simple
and rapid operation.
Stability analysis of oscillators
Close-in Phase noise analysis
Atomic frequency standard calibration
Active & passive component phase
stability measurement
ADEV, Modified ADEV, TVAR, MTIE etc
(with stable 32)
Temperature & Phase testing
Relative & Absolute counter display of
Frequency & Phase difference
Precision product characterisation
“National Measurement” level
metrology & analysis
• Unskilled operation
• Unequalled performance
• External PC enables low cost 2-3 year
• Flexible and easy to use
• Saves up to 40% of oscillator R&D time
The A7-MX is a bench or rack mount
instrument which interfaces with most
notebook or desktop PCs, using an RS232
or USB interface on the computer. The
instrument includes a differential multiply
and mix chain, and a 2 channel digital
phase comparator. An analog meter shows
The virtual panel provides control of measurement rate (tau),
and mode (narrowband, high resolution, or broadband). Repeater
indicators are provided to show the settings of controls on the
physical instrument. It is possible to store blocks of measurements
up to 32768 measurements into a computer file. Once a
measurement is started, the instrument will store the complete
measurement block internally, provide power is maintained.
This makes certain that data is never lost, even if the computer
crashes and has to be restarted. In order to make sure that a
long measurement run is not interrupted by a power failure, the
instrument may be powed from a battery supply of 24V. This will
automatically be used if line power should fail.
frequency offset or phase difference.
The digital display shows phase or fractional frequency offset depending
upon mode. The units and number of significant digits is adjustable.
There are 2 inputs on the front panel. One of these is for the phase/
frequency reference which will often be an atomic frequency
standard. The reference frequency can be 5 or 10MHz with
automatic switching. The other input is for the measurement signal,
also 5 or 10MHz, also with automatic switching.
There are pushbutton controls for phase/frequency mode, multiplier
ratio , filter selection, sampling rate (tau) and phase reset. There
are also a number of controls which adjust the analog meter
function. There are indicator lights to confirm that the reference and
measurement inputs are at the required level, and that the internal
phase locked multipliers are locked. The analog meter shows
fractional frequency difference with full scale ranges from +/-1x10-7
to +/-1x10-12, and phase differences with full scale ranges from +/10us to +/-100ps.
When the instrument is connected to a PC, the control positions are
read by the PC and displayed on the virtual control panel
On the rear panel is the broadband frequency input which can be
between 50kHz and 65MHz. Also on the rear panel are outputs to
an external timer/counter, and a switch which adjusts the analogue
meter time constant.
The instrument has two main modes, narrowband, high resolution,
and broadband. The selection between these modes is made on
the PC virtual control panel.
In narrowband, high resolution mode, the measured signal must
be at 5 or 10MHz. In this mode the instrument uses multiply and
mix techniques to increase the fractional frequency difference ( or
phase difference) between the measured input and the reference.
This improves the resolution of the digital phase comparator, and
results in a theoretical phase resolution of 0.125fs. The actual
resolution is noise limited to about 50fs. The corresponding
fractional frequency resolution is 1x10-13 in one second of
measurement time.
In broadband mode the multiply and mix is not used. The digital
phase comparator makes direct phase measurements with a
resolution of 12.5ps. This is comparable to the fastest frequency
counters and gives a fractional frequency resolution of 3x10-11
in one second of measurement time, or 2x10-12 with averaging
switched on.
When connected to a PC, the software provides 4 scalable
windows. One of these is the virtual panel and digital display. The
other 3 are data plot, Allan variance plot, and phase spectral density
(phase noise) plot.
Averaging mode may be selected from this window. If averaging is
off, the digital phase comparator makes single measurements at the
selected sampling rate. If averaging is on, the comparator operates
at the maximum sampling rate of 1ks/s. A block average reduces
the data rate to the slected sampling rate.
Dither mode may be selected from this window. Dither is a
technique which reduces unavoidable internally generated spurii to
below the noise floor, at the expense of an increase in noise floor.
For further details see operating manual.
The data window shows real time accumulation of the data as a
graph. The last 8 to 32768 data points may be shown on the graph.
A statistics display shows max, min mean, and standard deviation
for the data shown on the graph. The scaling of the y axis may be
auto, manual, or max/min.
The Allan variance window shows calculated Allan variance
for all data accumulated since the start of a run. If averaging is off,
single phase measurements are made at the requested sampling
rate and the statistic is true Allan variance. If averaging mode is
on, the statistic becomes modified Allan varaince. The graph title
correctly indicates this.
The Phase Spectral Density (PSD) window shows phase noise
as a graph of L(f) in units of dBc against offset frequency on a log
scale. Various window functions and averaging modes are provided.
The routines are identical to those used in the Industry standard
software “Stable32”.
The user can select the basic length of the FFT, and also the degree
of overlap. As data is accumulated, new FFTs are performed on a
mix of old and new data depending on the overlap parameter.
Each FFT result can either replace the last graph, be added to a
block average, or be used in a continous or exponential average.
All FFTs are correctly normalised for bin bandwidth, window ENBW,
window coherent gain, and nominal frequency.
Frequency data always has a fixed offset removed before being
used for the FFT calculation. Phase data has a fixed slope ramp
removed by linear regression. This avoids a large component in
the lower frequency bins which will distort the result, even when
windowing is used.
A mode is provided for the measurement of discrete components
(spurii). In this mode the scale is changed from L(f), dBc/Hz to
Power,dBc. Corrections for bin bandwidth and window ENBW
are removed. A flat top window is provided for measurement of
discretes, with scallop loss of only 0.01dB.
A7-MX Specification
NarrowBand / High Resolution Mode
a) Reference
b) Measurement (3 measurement inputs - see non standard options = A7-MY)
c) Input levels:
d) Max Freq difference (Filter off):
a) Counter A channel
5 or 10MHz sine wave 5 or 10MHz sine wave +0dBm to +13dBm into 50Ω
Low multiplier High multiplier N Type, Front Panel
b) Counter B channel
c) Counter external reference
100kHz square wave CMOS/TTL (frequency mode)
10us pulse CMOS/TTL (phase difference mode)
10us pulse CMOS/TTL (phase difference mode)
Nominal 3dB Bandwidths
Selectable bandwidth IF filter reduces measurement noise
200Hz, 60Hz, 10Hz
Fractional frequency multiplication
Measurement resolution
High multiplier 105
Low multiplier 103
Relative frequency difference mode
RMS resolution (filter 200Hz)
Using internal phase/freq.
meter (TIC) and Windows
Measured resolution
High multiplier
Low multiplier
1x10-13/gate time
1x10-12/gate time
Analogue Meter Resolution manually selected from 6 ranges
Full scale ranges (decade steps)
Time constant (linked to range)
Time constant multiplier
Displayed Noise
Zero drift
±1x10-7 to ±1x10-12
20ms to 10s
x1, x3, x10
<2x10-13 peak
Phase difference mode
(High resolution, Filter 200Hz)
RMS resolution (single measurement)
Analogue Meter
Full scale ranges (decade steps)
Displayed noise
Zero drift
±10us to ±100ps
<1ps peak
Short-term stability (noise floor)
Allan variance
<2x10 <5x10-16
1ms to 2000s
1, 2, 5 Steps
Sampling interval – gate time
Measurement Error
Input referred self generated spurii
103 multiplication
105 multiplication
Corresponding peak phase modulation
103 multiplication
105 multiplication
Allan Variance Error (due to each spur)
103 multiplication
105 multiplication
(See note 1)
<1ps typical at constant ambient temp
<5ps typical at constant ambient temp
10-12 divided by averaging interval (tau)
3x10-13 divided by averaging interval (tau)
Note: phase modulation spurii will be present at
multiples of the input frequency difference.
Note 1: Measured as the standard deviation of 1024 phase difference measurements/1.024s
Phase Spectral Density Specification (Close-In Phase Noise)
Phase noise measurement at very small frequency offsets
Identification of spurious components in the data which can distort an Allan variance plot
Maximum offset frequency
500Hz (at 1ks/s)
Close-in Phase Noise floor
-100dBc/Hz @ 10mHz offset (0.01Hz offset)
-115dBc/Hz @ 100mHz offset (0.1Hz offset)
-130dBc/Hz @ 1Hz offset
-150dBc/Hz @ 100Hz offset
-160dBc/Hz @ 500Hz offset
Note: 5 or 10MHz reference must be present at reference (front panel) input of A7-MX
50kHz to 65MHz
Input levels
50kHz to 1MHz
1MHz to 50MHz
50MHz to 65MHz
224mV rms (0dBm) to 2V rms (+19dBm)
70.7mV rms (-10dBm) to 2V rms (+19dBm)
224mV rms (0dBm) to 2V rms (+19dBm)
BNC rear panel
Resolution (nominal)
Broad- and Narrowband
BNC, rear panel
11 digits /second of gate time (averaging on)
Noise Floor (allan variance) (measured at 10MHz, 10dBm input)
Averaging off
All gate times
Averaging on
Averaging factor 10
Allan variance
< 2x10-9
< 2x10-10
< 2x10-11
(Averaging factor = gate time/1ms)
< 2x10-11
< 6x10-12
< 2x10-12
Virtual Front Panel
Absolute or relative (normalised) frequency display
User entered normalisation frequency
Allan Variance graph
Frequency data graph
Data storage of phase or frequency data
Temperature Range
Operating: 10C to 35C (± 5C within this range during measurement) Storage: -10C to 60C
2U 19" rack unit WxHxD(max) 450(483)x88(96)x345(370) <9kg
Power Supply120/ 240V AC line 50W max 24V DC battery backup with automatic switching.
Current consumption 1Amp max. With option 1 add 1Amp
Supplemental Performance Data (SPD)Please contact Quartzlock for SPD and applications note.
Typical Narrowband Performance (PSD)
A7-MX Phase Noise Floor (10MHz) – Narrowband high resolution mode. 500mHz to 500Hz offset
A7-MX Phase Noise Floor (10MHz) – Narrowband high resolution mode. 300uHz to 500Hz offset
Typical Narrowband Performance
Graphs (AVAR)
A7-MX Allan Variance (10MHz) – Narrowband high resolution mode. 10-3s to 10s
(red plot is predicted)
A7-MX Allan Variance (10MHz) – Narrowband high resolution mode. 10-1s to 8x10-4s
(red plot is predicted)
Typical Broadband Performance
Graphs (PSD & AVAR)
The ongoing
of Quartzlock’s
Signal Stability
Analyzer line
illustrates our
future product
road map
A7-MX Signal
Stability Analyzer
– available now
A7-A Analogue
Frequency & Phase
Difference Meter –
available now
Broadband Phase noise floor. 300mHz to 500Hz offset
A7-MX (ULN) Ultra Low
Noise Signal Stability
Analyzer 1 to 20MHz
– 180 days ARO
A7-ATE Automatic
PC controlled Signal
Stability Analyzer
– 180 days ARO
A7-MXE Microwave
Signal Stability
Analyzer Extended
Frequency versions to
28GHz – 2010
Broadband Allan variance noise floor. 100ms to 1000Hz offset
(red plot is predicted)
A7-MX Block Diagram
Figure 2
(see page 8)
Figure 1
(see page 8)
Ordering Information – Options
0Add Seamless Battery Back-up Switch & 24V dc input
36Training (contact Quartzlock)
1Distribution Card
1 Input
4 Outputs
40Power splitter and cable set for noise floor verification
2Delete internal phasemeter and software – Order model A7-A
Option 27 is an internal rubidium oscillator refernce. It may be
preferred that an external reference be supplied in light of Quartzlock
2009 rubidium product line – ask Quartzlock (costs are similar). We
recommend the Quartzlock model A10-MX Ultra Low Noise Rubidium
Frequency Reference.
18Add Additional 1 to 5 Years Warranty
(18.1 = 1 Year ... 18.5 = 5 years)
27Add Ultra Low Phase Noise Rubidium Oscillator
(see A10-Y and A10-MX specifications)
32Add Stable 32 Analysis Software
49Phase noise out to 5kHz offset
Non standard options – ask Quartzlock
A7-MX Technical Description
The principle behind the A7-MX is to increase the resolution of a digital
phase meter. This is achieved by multiplying the frequency to be measured to a higher
frequency, and then mixing it down to a lower frequency using a local oscillator derived
from the frequency reference. The principle is illustrated in Figure 1 (see page 6), and has
been made the basis of a number of instruments in the past. The relationship is shown
for signals down the mix/multiply chain for an input signal with a difference of delta f
from the reference, and also for a signal with no frequency difference, but with a phase
difference of delta t. (An important clarification is that “phase” difference beteween two
signals can either be measured either in time units or angle units. A measurement in time
units does not specify or imply the frequency of the signals. A measurement in angle units
(radians) needs a prior knowledge of the frequency. Throughout this description, phase
will be measured in time units) It should be noted that a frequency multiplication multiplies
a frequency difference but leaves a phase difference unchanged. Conversely, a mixing
process leaves a frequency difference unchanged, but multiplies a phase difference. When
the frequency differences are converted to fractional frequency differences by dividing
by the nominal frequency, it will be seen that the multiplication factors for frequency and
phase are the same.
The big disadvantage in the simple approach shown in Figure 1 is that phase drift with
temperature will be excessive. As rate of phase drift is equal to the fractional frequency
difference , the measurement of the frequency of an unknown device will be in error. For
example, a drift rate of 10ps per second in the first multiplier in the Figure 1 diagram will
be multiplied to 1ns per second at the output. This is equivalent to a 1 x 10-12 frequency
error due to drift. Phase drift may occur in mixers and multipliers, but more especially
in multipliers. If harmonic multipliers are used, drift will occur in the analogue filters that
are used to separate the wanted harmonic from the subharmonics and unwanted mixer
products. If phase lock multipliers are used, phase drift will occur in the digital dividers.
To overcome the drift problem, the multiplier/mixer chain is made
differential, ie the reference signal is processed in an identical way to the unknown.
When the two channels are subtracted, any drift in the multipliers will cancel. The method
of doing this can be seen from the functional block diagram of the A7-MX, FIG 2. The
first stage of the processing for both the reference and measurement channels is a
multiplication by 10 (20 for 5MHz inputs). The multipliers are phase locked loops with a
VCXO of 100MHz locked to the input by dividing by 10 (20 for 5MHz inputs). The phase
detectors used are double balanced diode mixer type phase detectors. These exhibit
the lowest phase drift with temperature. The dividers used are ECL types with very small
propagation delays. The outputs of the dividers are reclocked using a D type flipflop
clocked by the 100MHz VCXO signal. In this way the divider delay is made equal to the
propagation delay of one D type, approx 500ps. As a further refinement, the reclocking D
types for the reference and measurement channels are closely thermally coupled. As the
divider propagation delays are equal to the reclocking flipflop delays, the tracking between
the reference and measurement channels is exceptionally good.
The VCXO signals at 100MHz also drive double balanced FET mixers for the first down
conversion to 1MHz. The 99MHz LO is common to both the reference and measurement
channels, and is obtained from a 2 way passive inductive type power splitter. The output
from the mixers is filtered by diplexer type filters to remove the image at 199MHz and
the signal and LO feed through at 100MHz and 99MHz respectively. The wanted IFs at
1MHz are passed without further processing to the second multipliers. The avoidance of
IF amplifiers at this point avoids drift which could be substantial as the propagation delay
of the IF amplifier could be several 100 nanoseconds. IF amplifiers are used for the first IF
take off points to the IF processing board. The first IFs are used when a multiplication of
103 is selected.
The second multipliers are nearly identical to the first multipliers with the difference that the
phase lock loop dividers divide by 100. This multiplies the first IF of 1MHz to the second
VCXO frequency of 100MHz. The second downconvert is identical to the first, with the
second IFs being passed to the IF processing board.
The first and second multipliers/mixers for the reference and measurement channels are
built symmetrically on one PCB (Printed Circuit Board). In order to ensure the best possible
temperature tracking beween the channels, the PCB is in good thermal contact with a
thick metal baseplate. This minimises rapid temperature changes between the channels.
The two pairs of IF signals (sine wave) are passed to the IF processing PCB. The two
pairs are the outputs from the first and second downconvertors. They correspond to final
multiplication factors of 103 and 105. Also on the IF processing board is the 99MHz LO
generation and phase lock. A 10MHz unmultiplied signal is passed to the IF processing
board from the reference channel on the Multiplier board.
The 1MHz IFs could be divided down and measured directly by the frequency counter,
which would make a time difference measurement between the measurement and
reference IF signals. In this way the difference between the channels would be measured
and any drift would cancel. Although this would work for a phase measurement, there
The detailed process is as follows:
The 10MHz reference from the multiplier board (this is derived from the reference input
without multiplication) is divided by 25 to 400kHz. The 400kHz is then divided by 4 to give
two quadrature signals at 100kHz. These signals are filtered using low pass filters to give
100kHz quadrature sine waves. The 1MHz multiplied reference IF (after limiting) is delayed
by 250ns to give quadrature square waves. These operate dual switching mixers with the
100kHz quadrature sine waves as the linear inputs. The outputs are combined to form an
image reject mixer, with the wanted sideband at 900kHz and the unwanted sideband at
1.1MHz. The 900kHz sideband is filtered in an LC bandpass filter to further remove the
unwanted sideband and the 1MHz feed through. This output is used as the linear input to
a further switching mixer which downconverts the 1MHz multiplied measurement IF (after
limiting) to the final IF of 100kHz. The final IF is filtered in an LC bandpass filter to remove
the unwanted sideband at 1.9MHz and any other mixer products. The measurement and
reference channels have now been combined into a single IF of 100kHz with the drift and
LO instabilities removed. This IF is now further processed to provide the counter outputs
as will be described in the next paragraphs.
The measurement bandwidth of the system has been defined up to this
point by the loop bandwidths of the phase lock multipliers and the bandwidth of the
100kHz LC filter. The 3dB bandwidth is about 8kHz. This means that fourier frequencies
further displaced from the carrier of greater than 5kHz will be attenuated. The phase
measurement process essentially samples the phase of the unknown signal relative to
the reference at a rate determined by the selected tau (selectable from 1ms to 2000sec).
As with any sampling process, aliasing of higher frequency noise into the baseband will
occur. Thus further band limiting of the 100kHz IF is desirable before measurement takes
place. The A7-MX has a crystal filter following the LC filter with selectable bandwidths of
nominally 10Hz, 60Hz, and 200Hz. For most Allan variance plots at least the 200Hz filter
should be used. The use of a filter will reduce the noise floor of the instrument which is
desirable when measuring very stable active sources and most passive devices.
After the crystal filter the 100kHz IF is limited to a square wave by a zero crossing
detector. This output is made available to the counter A channel when frequency mode
is selected. Both the 100kHz IF containing the multiplied frequency difference information
and the 100kHz unmultiplied reference are divided in identical divider chains down to 1kHz
to 1mHz in selectable decade steps. The output of the dividers trigger digital ( clocked)
monostables to generate 10us pulses which are routed to the counter A and B channels
when phase mode is selected.
When the internal digital phase comparator is in use, the phase of both the 100kHz
reference and the 100kHz multiplied IFs are measured relative to the unmultiplied 10MHz
reference. The digital phase comparator then calculates the resulting phase difference
or fractional frequency offset depending upon the selected mode. The digital phase
meter also applies averaging if selected. It has internal storage sufficient for 32768
measurements. The RS232 interface to the computer uses full handshaking to prevent
data loss. The internal phase comparator has a resolution of 12.5ps, obtained by using an
analogue pulse expander circuit.
The meter circuit also uses the 100kHz IF and 100kHz reference. The basis of the circuit
is a differential frequency to voltage convertor. However in order to increase the resolution
of this circuit, a further stage of multiplication and mixing is employed. The 100kHz
reference is divided down to 500Hz. This frequency is then multiplied to 4.9995MHz using
a phase lock loop with a divider of 9999. The 100kHz measurement IF is multiplied to
5MHz also using a phase lock loop. Finally the 5MHz signal and the 4.9995MHz signal
are mixed together to give an IF of 500Hz. An additional fractional frequency multiplication
of 104 results. On the least sensitive meter range this 500Hz IF varies in frequency from
0Hz to 1kHz. The 500Hz measurement IF and the 500Hz reference both trigger digital
monostables which produce very accurate fixed width pulses . These pulses are used to
gate an accurate positive and negative current into a chopper stabilised summing amplifier.
The output of the summing amplifier is a voltage which drives the moving coil centre zero
meter. The meter circuit has 4 decade ranges which in conjunction with the 2 multiplication
factors of the main comparator results in 6 meter ranges with full scale deflections of 10-7
to 10-12.
The meter time constants are linked to the meter range, however may be increased
if desired using a switch mounted on the rear panel.
Contact us:
Europe & US
Telephone: +44(0)1803 862062
ISO 9000
NIST Traceable
• Specification subject to change without notice
• This issue replaces all previous issues
• This specification does not form part of any contract
• ISO 9001 • CE mark where applicable • © Copyright Dartington Text 2009
• Doc No: PG Issue 14 (June 2009)
would be no way of making a conventional frequency measurement. The IFs cannot
be directly subtracted in a mixer as they are both nominally 1MHz, and the nominal
difference frequency would be zero. In order to avoid this problem, the multiplied reference
IF is frequency shifted to 900kHz using an LO of 100kHz derived from the unmultiplied
reference. The 900kHz is then mixed with the 1MHz measurement channel IF to give a
final IF of 100kHz. This final IF contains the multiplied frequency difference, but drift in the
multipliers and phase noise in the common 99MHz LO will have been canceled out.
Fax: +44(0)1803 867962
The Quartzlock logo is a registered trademark. Spec subject to change without notice & not part of any contract. Copyright © 2009. Issue 06.09
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