Phase stability study of a HPR

Phase Stability Studyof a

Harmonic Phase Reference

Jan 09

© Copyright 2009 2

Outline

● Introduction

● Harmonic phase reference (HPR) and Error Bounds

● Phase alignment

● Measurement Noise

● Warm-up time

● Phase stability study under different external conditions

● Summary

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Introduction

● Goal● Presenting the different studies, performed on comb generators to establish a

worst-case error bound on their phase characteristic

● Motivation● Accurately measuring the voltage and current at the input and output ports of a

nonlinear device using a Large-Signal Network Analyser (LSNA), which can be based on a Vector Network Analyser (VNA), e.g. ZVA24 [1]

● Requires additional calibrations on top of the relative calibration● Absolute Amplitude calibration: Calibrated Power Sensor ● Absolute Phase calibration: Calibrated Harmonic Phase Reference (HPR)

● The phase stability of the HPR impacts the phase accuracy of the LSNA measurements

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Harmonic Phase Reference

● What?● a comb generator including proper padding● driven by a synthesiser at frequency f

o

● What is important for the absolute phase calibration?● a fixed phase relationship between the combs● an arbitrary delay can always be applied to the phase characteristic

Comb generator

fo = 600 MHzInput pulse = sine wave

Output = pulse ns

[V]

GHz

Pulse Fundamental and harmonics

f0

2f0

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Contributions to the Error Bounds on the HPR Phase

● Systematic errors, introduced by the calibration process● Traceability to NIST has been established● Not discussed in this presentation

● Intrinsic device noise in Comb Generator● Always present in the measurements

● Phase stability impacted by external factors● Temperature variations● Variations in applied input power● Variations in applied bias voltage● Impact of the nonlinearities of the source● Impact due to load variations

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Measurement Setup to study HPR Stability

● Study of stability only requires a comparison between measurements● Using the MT4463 [2] which is proven to be very stable after warm-up time to

measure incident and reflected waves

● Observing the voltage waveforms a1 and b

2 under varying conditions and

studying the phase variation of b2

● Two Problems● Arbitrary delays in repeatable measurements of b2 require proper phase alignment

for correct phase characterisation● Measurement noise converts into phase uncertainty and hides phase error on HPR

● Need to estimate the phase error due to the measurement noise● This also includes the intrinsic noise generated by the comb generator

Pin

a1

50Ω

Combgenerator

Reference planes

fo MT4463

b1

b2

a2

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Elimination of Arbitrary Delay

● The error bound on the phase as function of frequency under varying conditions is influenced by the method to eliminate the arbitrary delay

● Challenge: for each measurement, determine the delay such that the phase variation across comparable measurements is minimised for all spectral components

● Different methods to eliminate the delay● Apply a delay to the signal such that the phase of the fundamental frequency

becomes zero● Apply a delay to the signal such that the difference between the signals is

minimised for all spectral components● Use system identification for optimal extraction of delay [3],[4]

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5 10 15 20Harmonic Index

0.05

0.1

0.15

0.2

0.251 degrees

Phase Alignment

To determine phase error specifications, NMDG applies the latter (red) method

Blue = delay signals such that phase of fundamental is zeroRed = delay signals to minimise the error for all spectral components

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Estimation of Phase Error Due to Measurement System

● Measurement noise converts into phase error

● This phase uncertainty adds up to the phase variations of the HPR

Measurement Noise

One Spectral Componentof comb generator

LargePhase deviation

LargeSpectral Component

SmallSpectral Component

SmallPhase deviation

AmplitudeUncertainty

5 109 11010 1.5 1010 21010 2.5 1010Hz

0.4

0.2

0.2

0.4

0.6

0.8

11 degrees

1000 comb generator measurementsAfter proper phase alignment: Total phase uncertainty Phase uncertainty due to measurement noise

1 - uncertainty

ConclusionPhase variation of comb generator cannotbe distinguished from measurement noise

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5 10 15 20 25 30 35 40Time min

3

2

1

1

2

3Phase deg

Minimal Warm-up Time

● Comb Generator● Nominal input power: +10 dBm, nominal biasing voltage: +5V, f0 : 600 MHz

● Measurement Procedure● Apply nominal input power and nominal biasing voltage● Perform 100 measurements after {0, 1, 3, 6, 10, 15, 21, 28, 36, 45, 55} minutes

● Calculate an “average pulse” using the proper alignment at each time slot● Compare the 10 “average pulses” against the “average pulse” after 55 minutes after

proper alignment

● Conclusion● After 3 minutes warm-up● Phase deviation < 1 degree

Cold Start

2f0

Phase variations of each harmonic vs. time

f0


5 10 15 20 25GHz

1

0.75

0.5

0.25

0.25

0.5

0.75

11 degreesLong term sensitivity 3 days,4 measurements

Long – Term Stability

● Comb Generator● Nominal input power: +10 dBm, nominal biasing voltage: +5V, f

0 : 600 MHz

● Measurement Procedure● Apply input power● Wait 30 minutes● 1000 measurements with interval of 5 seconds

● Calculate an “average pulse” using the proper alignment● Repeat 4 times, spread across 3 days

● This results in 4 “average pulses” being compared after alignment with each other

● Conclusion● Phase Variations of

0.5 degrees are observable


9.25 9.5 9.75 10 10.25 10.5 10.75 11Input power dBm

3

2

1

1

2

3Phase deg

Power Sensitivity

● Comb Generator● Nominal biasing voltage: +5V, f

0 : 600 MHz

● Measurement Procedure● Applying nominal input power and nominal biasing voltage● Wait 30 minutes● Stepping input power from +9 dBm to +11 dBm in steps of 0.1 dBm (21 steps)● For each power setting: 1000 measurements

● Calculate an “average pulse” using the proper alignment● Compare the phase of each “average pulse” with “average pulse” for nominal input

power of +10 dBm

● Conclusion● Power variation needs to be

limited to +/- 0.25 dBm

to limit phase variation

within 1 degree

2f0

Phase variations of each harmonic vs. input power


4.8 4.9 5.1 5.2Bias voltage V

6

4

2

2

4

6Phase deg

Bias Sensitivity

● Comb Generator● Nominal input power: +10 dBm, f

0 : 600 MHz

● Measurement Procedure● Applying nominal input power and bias voltage● Wait 30 minutes● Stepping biasing voltage from +4.8 to +5.2 Volt in steps of 0.05 Volt (9 steps)● For each bias setting: 1000 measurements

● Calculate an “average pulse” using the proper alignment● Compare the phase of each “average pulse” with “average pulse” for nominal biasing

voltage of +5 Volt

● Conclusion● Bias voltage variation

needs to be controlled

within 50 mV due to

phase variation of second harmonic

2f0

Phase variationsof each harmonicvs. bias voltage


Source and Load Sensitivity

● Using the comb generator as HPR requires proper padding● Minimising mismatch effects● Limiting the peak voltage to avoid compression of LSNA receivers● The comb generator used in this study is padded with 20 dB

● Source sensitivity● The HPR is driven by the synthesiser used in the LSNA setup● The phase characteristic can be sensitive to harmonic distortion (HD)● It is assumed that the synthesiser has a HD of -30 dBc in worst case

● Load sensitivity● The HPR is connected to different test sets● A test set presents a certain load match, which can impact the phase

characteristic● It is assumed that the test set has a return loss of 20 dB or better

● A special measurement setup is used to inject signals at fundamental and harmonics to simulate different harmonic distortions and return losses


Source and Load Sensitivity: Measurement Setup

Pin a1

b1

b2

a250ΩRF1

fo

RF2

Vbias

Combgenerator

HPR

Second source (RF2) to inject a waveform

Source sensitivity: inject waveform at 2f0 and 3f

0

Load sensitivity: inject waveform at f0, 2f

0, 3f

0


Source Sensitivity


● Measurement Procedure● Applying nominal input power and nominal biasing voltage● Wait 30 minutes● Injecting different powers at second and third harmonic while rotating the phase

to simulate all possible harmonic distortion situations up to -30 dBc● Processing of measurements in the same way as HPR under nominal conditions

● Calculate an “average pulse” using the proper alignment for all measurements● Determine the uncertainty of all pulses, compared to the “average pulse”

● Conclusion● Harmonic Distortion of -30 dBc

can lead to a phase deviation of

1 degree

2.5 5 7.5 10 12.5 15 17.5 20GHz

0.5

1

1.5

2

2.5

3

3.5

41 degrees Source sensitivity

2f0

Phase uncertaintydue to measurementnoise

Phase deviationdue to harmonicdistortion


2.5 5 7.5 10 12.5 15 17.5 20Hz

1

2

3

4

51 degrees Load sensitivity

Load Sensitivity


● Measurement Procedure● Applying nominal input power and nominal biasing voltage● Wait 30 minutes● Injecting different powers at fundamental, second and third harmonic while

rotating the phase to simulate all possible load mismatches up to 20 dB return loss

● Same processing as for source sensitivity

● Conclusion● Mismatch can lead to some small

phase deviation

2f0

Phase uncertaintydue to measurementnoise

Phase deviationdue to mismatch


Summary

● Discuss the harmonic phase reference and its phase specification● Discuss the phase alignment and error contributions to the phase● Determine the minimal warm-up time● Discuss the sensitivity to external factors

● Power sensitivity● Bias sensitivity● Sensitivity to harmonics generated by the synthesiser● Sensitivity to different load matches

● Explain the measurement procedure for each sensitivity study

● For the commercial Phase Reference, these procedures are repeated on a dense grid

For more technical information, please contact [email protected]


References

[1] NM300, ZVxPlus, http://www.nmdg.be/files/ProductNoteNM300.pdf

[2] MT4463 Datasheet, http://www.nmdg.be/files/MT4463DataSheet.pdf

[3] Frans Verbeyst, Rik Pintelon, Yves Rolain, Johan Schoukens and Tracy S. Clement, “System Identification Approach Applied to Drift Estimation”,Instrumentation and Measurement Technology Conference, IMTC 2007,Warsaw, Poland, May 1-3, 2007.http://www.nmdg.be/library/contributions/IM-7123.pdf

[4] Frans Verbeyst, “Contribution to Large Signal Network Analysis”,PhD dissertation, September 2006.http://www.nmdg.be/index_jump.html?goto=library_center

Phase stability study of a HPR

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