Application Report
SCAA120B – September 2012 – Revised August 2017

How to Measure Total Jitter (TJ)
Julian Hagedorn, Falk Alicke, and Ankur Verma .................................................................. SVA/SDS/CTP
ABSTRACT
Today, the jitter specification, TJ, is used in more and more systems, at the same time the jitter
requirements get lower and lower. Clock generators or jitter cleaners like the CDCM6208 meet those
tough jitter specifications for most systems (for example, TMS320TCI66xx DSP-based systems; seeHardware Design Guide for KeyStone I Devices (SPRABI2). The other side of the coin is that themeasurement equipment has to be feasible to measure the low-noise clock generators. Therefore, themeasurement equipment has to have a lower noise floor than the device under test. This can be achievedby minimizing the noise sources within the measurement equipment.
This application report describes the recommended measurement techniques for TJ. It includes thedescription of the techniques to minimize the noise sources of the measurement equipment. TheCDCM6208 characterization setup is used as an example throughout the application report.

123456789ContentsIntroduction ................................................................................................................... 2
1.1
Noise Sources in an Oscilloscope ................................................................................ 2Comparison: Phase Noise Analyzer Versus Oscilloscope ............................................................. 3
TJ Characterization Setup................................................................................................... 4
Measurement Results ....................................................................................................... 5
Slew Rate Amplifier Alternatives ......................................................................................... 10Tradeoffs .................................................................................................................... 10Digital Serial Analyzer With DPOJET Software ....................................................................... 10Conclusion .................................................................................................................. 11References .................................................................................................................. 11
List of Figures

1Total Jitter Components .................................................................................................... 22Oscilloscope Noise Sources ............................................................................................... 33Slew Rate Impact on Measured Clock .................................................................................... 3

4Traditional TJ Measurement Setup ........................................................................................ 4

5PNA Connection to Measure Random Jitter ............................................................................. 5

6

Improved TJ Measurement Setup With ONET1191P ................................................................... 57122.88 MHz (Integer): TJ = 18.335 ps .................................................................................... 68122.88 MHz (Integer) With ONET1191P: TJ = 7.722 ps ............................................................... 69156.25 MHz (6-Bit Fraction): TJ = 49.356 ps ............................................................................ 710156.25 MHz (6-Bit Fraction) With ONET1191P: TJ = 40.840 ps ...................................................... 711156.25 MHz (20-Bit Fraction): TJ = 63.69 ps ............................................................................ 812156.25 MHz (20-Bit Fraction) With ONET1191P: TJ = 54.88 ps ...................................................... 813312.5 MHz (Integer): TJ = 17.763 ps ..................................................................................... 914

312.5 MHz (Integer) With ONET1191P: TJ = 8.205 ps ................................................................. 9SCAA120B – September 2012 – Revised August 2017
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How to Measure Total Jitter (TJ)

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Introduction

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1

Introduction
Jitter is a time variant noise component that impacts the phase of a signal. Total jitter includes twocomponents; bounded (or deterministic) jitter and unbounded (or random) jitter.
Deterministic jitter is a predictable and repeatable behavior which can be expressed as a peak-to-peakvalue. Random jitter is the unbounded jitter part of TJ. It is mainly thermal noise, flicker noise or shotnoise.
Specifiedfor a Specific
Specifiedas
aspeak-to-peak
pk-pk for a specific
BER BER

Total
JitterEffectively Unbounded

Unbounded, RMS

Bounded,Bounded,peak-to-peakpk-pk

RandomJitterDeterministicJitter

BoundedJitterPeriodicJitterDataDependent

Figure 1. Total Jitter Components
A good technique to measure TJ uses a high-end digital sampling oscilloscope. This oscilloscopes need tohave a better noise floor than the device under test, otherwise the performance of the device under test
would be degraded and worsen by the noise of the oscilloscope. The noise floor in oscilloscopes isspecified as jitter noise floor or jitter measurement floor.
In most cases, the given jitter measurement floor of an oscilloscope is only valid with a best case signal.
This means that the input signal has to meet a certain slew rate.

1.1

Noise Sources in an Oscilloscope
In an Agilent application report the jitter noise floor is calculated as:22
 Oscilloscope Noise 
Jitter Measurement Floor = + (Sample Clock Jitter)2
Slew Rate(1)

SampleClockJitter is also called intrinsic jitter. It describes the accuracy of the data sampling points andcan be seen as horizontal noise impact.
OscilloscopeNoise describes the noise contributed by the oscilloscope itself (mainly voltage noise orvertical noise impact).

2

How to Measure Total Jitter (TJ)

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Comparison: Phase Noise Analyzer Versus Oscilloscopewww.ti.com

Figure 2. Oscilloscope Noise Sources
The simplified input of an oscilloscope is made of an analog-to-digital converter (ADC) which is clocked by
the sampling clock. Additionally, there is the input gain stage which injects the oscilloscope noise.

Figure 3. Slew Rate Impact on Measured ClockIn Figure 3 the slew rate of a clock signal was increased whereas the oscilloscope noise is equal. Theillustration shows that a signal with a slow slew rate is more susceptible to oscilloscope noise than signals
with a high slew rate.
As a consequence, either an oscilloscope which accepts lower slew rate in combination with a very goodjitter measurement floor, or a higher signal slew rates has to be used to measure a device with less impact
from the oscilloscope. During the device characterization of the CDCM6208 a limiting amplifier(ONET1191P) from TI was used to increase the slew rates of the CDCM6208. The limiting amplifier iscalled ONET1191P or slew-rate amplifier for the remainder of this document.

2Comparison: Phase Noise Analyzer Versus Oscilloscope
Table 1 summarizes TJ and random (or RMS) jitter measurement test results with the oscilloscopecomparing jitter with and without the ONET1191P. As it can be seen using the ONET1191P, the datameasurement on the phase noise analyzer (PNA) and the oscilloscope correlates very well.

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TJ Characterization Setup

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RJ or RJ with ONET1191P represents the random jitter component of a TJ measurement. TJ or TJ withthe ONET1191P represents the TJ measurements. PNA describes the RMS jitter measurements takenwith a PNA with an integration range of 10 kHz to 20 MHz.
Table 1. Jitter Measurement[ps-rms][ps-rms][ps-rms]

ps-pp

ps-pp

PNA (1)RJ

RJ WITH
ONET1191P (1)TJ

TJ WITH
ONET1191P

122.88 MHz (integer)

0.263

1.252

0.507

18.3357.722

156.25 MHz (6-bit fractional)

0.474

1.715

0.959

49.35640.84

156.25 MHz (20-bit fractional)

0.635

2.06

0.773

63.69

54.88

312.50 MHz (integer)

0.255

1.212

0.483

17.763

8.205

FREQUENCY (DIVIDERFRACTION)(1)

3

NOTE: The difference between PNA values and RJ with ONET1191P is because the ONET1191P worsens the signal by its
additive jitter

TJ Characterization Setup
During TJ characterization of CDCM6208, the setup shown in Figure 6 was used.

Figure 4. Traditional TJ Measurement Setup

4

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Measurement Results

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Figure 5. PNA Connection to Measure Random Jitter

Figure 6. Improved TJ Measurement Setup With ONET1191P

4Measurement Results
Figure 7 through Figure 14 show the measured results for TJ with and without the ONET1191P withdifferent output frequencies.

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Figure 7. 122.88 MHz (Integer): TJ = 18.335 ps

Figure 8. 122.88 MHz (Integer) With ONET1191P: TJ = 7.722 ps

6How to Measure Total Jitter (TJ)

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Measurement Results

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Figure 9. 156.25 MHz (6-Bit Fraction): TJ = 49.356 ps

Figure 10. 156.25 MHz (6-Bit Fraction) With ONET1191P: TJ = 40.840 ps

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Measurement Results

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Figure 11. 156.25 MHz (20-Bit Fraction): TJ = 63.69 ps

Figure 12. 156.25 MHz (20-Bit Fraction) With ONET1191P: TJ = 54.88 ps

8

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Measurement Results

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Figure 13. 312.5 MHz (Integer): TJ = 17.763 ps

Figure 14. 312.5 MHz (Integer) With ONET1191P: TJ = 8.205 psSCAA120B – September 2012 – Revised August 2017
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Slew Rate Amplifier Alternatives

5

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Slew Rate Amplifier Alternatives
As an alternative to the ONET1191P, any other differential buffer with a rise and fall time smaller than 100
ps can be used.
CDCLVP12xx or LMK00301 could be used as an alternative, but the rise and fall times are still too slow.
Additionally, oscilloscope manufacturer LeCroy has a proprietary solution called SDA-LNES (Low-noiseedge sharper).

6Tradeoffs
Using a slew-rate amplifier to lower the oscilloscope noise impact, the random jitter component of thedevice under test is increased. Each component in the measurement chain worsens the random jitter. The
impact can be calculated with this formula:2222)2
Total Jitter = (JitterJitter DUT+2Jitter
SlewSlew
RateRate
AmplifierDUT)+ (JitterAmplifier)2(2)High slew rates require oscilloscopes with a high sample rate (at least 40 GSPS) and enough memory tocapture a signal over a long time. 40 GSPS means that the oscilloscope measurement point resolution is25 ps. As an example, a 20 GSPS oscilloscope measures every 50 ps. Due to the fact that theONET1191P has a typical rise time of 45 ps, a 40-GSPS oscilloscope is mandatory to measure the signal
edge correctly. Otherwise, the under sampling effect adds additional jitter to the measurement.

7

Digital Serial Analyzer With DPOJET Software
As an example for Jitter measurement, Tektronix 16 GHz 50GS/s Digital Serial Analyzer with DPOJET
software can be used for eye width/height and jitter analysis. Common DPOJET measurement parameters
configuration used are shown in Table 2. Listed in this instruction set is the recommended process for theeye diagram measurement, using a Tektronix 16-GHz oscilloscope with DPOJET software. This software
overlays all the possible unit intervals of data and conducts the horizontal and vertical measurements. The
vertical measurement is in terms of voltage and the horizontal is in terms of UI.
Table 2. DPOJET Measurement Parameters Configuration
MEASUREMEN
T

10

EDGE
S

CLOCK
RECOVERY

RjDj

FILTERSGENERALGLOBAL

BIT CONFIG.

TJ@BER

Data

Method: PLLCustom PW
PLL Mode:Type I
Loop BW:FPCLK/40
Apply to All:
ApplyPattern
Detection/Control: Manual
Pattern Type:
Arbitrary
Window Length
5UI Target BER:
1 E-10
Apply to All:Apply

HPF (F1)
Filter Spec:
2nd Order
Freq (F1):FPCLK/40
LPF (F2)
Filter Spec:No Filter
Apply to All:
ApplyDefault

Default—

Width@BER

Data

Same Above

Same Above

Same Above

Default

Default—

Height————Default

Default

Bit Type: All Bit

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Conclusion

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8Conclusion
Total jitter has to be measured with an oscilloscope that has a reasonable jitter measurement floor smaller
than 300 fs. In today’s oscilloscopes, an external slew rate amplifier must be used to achieve such low
jitter measurement floors.
In addition, the oscilloscope must have at least 40 GSPS to ensure a proper amount of sampling points tomeasure the fast slew rate of the slew rate amplifier and to prevent under sampling. Take the amount ofscope memory into account, t as well, because the scopes must have a minimum number of samples tocalculate TJ.

9References
1. CDCM6208 2:8 Clock Generator, Jitter Cleaner with Fractional Dividers (SCAS931)
2. Understanding the Jitter Specification in Oscilloscopes; EETimes
3. SDA-LNES; LeCroy

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Revision History

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Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from A Revision (December 2012) to B Revision ........................................................................................... Page•12

Added the Digital Serial Analyzer With DPOJET Software section ............................................................... 10Revision History

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