Apparatus for and method of measuring a jitter

• US 6,775,321 B1
• Filed: 10/31/2000
• Issued: 08/10/2004
• Est. Priority Date: 10/31/2000
• Status: Expired due to Fees

• Current Assignee: Advantest Corporation
• Original Assignee: Advantest Corporation
• Inventors: Yamaguchi, Takahiro, Watanabe, Toshifumi, Ishida, Masahiro, Soma, Mani
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/703,469
• Time in Patent Office: 1,379 Days
• Field of Search: 375/226, 375/371, 702/69, 324/76.77, 324/86
• US Class Current: 375/226
• CPC Class Codes: G01R 29/26 Measuring noise figure; Measuring signal-to-noise ratio

Abstract

A signal under measurement is transformed into a complex analytic signal using Hilbert transformation to estimate an instantaneous phase of the signal under measurement from the complex analytic signal. A least mean square line of the instantaneous phase is calculated to obtain a linear instantaneous phase of the signal under measurement, and a zero-crossing timing of the signal under measurement is estimated using an interpolation method. Then a difference between the instantaneous phase and the linear instantaneous phase at the zero-crossing timing is calculated to estimate a timing jitter sequence. A jitter of the signal under measurement is obtained from the jitter sequence.

Claims

1. A jitter measurement apparatus comprising:

an analytic signal transformer for transforming a signal under measurement into a complex analytic signal;

an instantaneous phase estimator for obtaining an instantaneous phase of the signal under measurement from the complex analytic signal transformed by said analytic signal transformer;

a linear instantaneous phase estimator for obtaining a linear instantaneous phase of an ideal signal that does not contain a jitter by obtaining a least mean square line of the estimated instantaneous phase;

a zero-crossing timing estimator for obtaining a zero-crossing timing of the signal under measurement using any one of an interpolation method and an inverse interpolation method;

a timing jitter estimator for calculating a difference between an instantaneous phase value of the signal under measurement and a linear instantaneous phase value of the ideal signal at the zero-crossing timing estimated by said zero-crossing timing estimator to obtain a timing jitter sequence; and

a jitter detector to which the timing jitter sequence is supplied for obtaining a jitter of the signal under measurement.

2. The jitter measurement apparatus according to claim 1 further comprising:

a period jitter estimator to which the timing jitter sequence is inputted for calculating its differential sequence and for outputting a period jitter sequence of the signal under measurement to supply it to said jitter detector.

3. The jitter measurement apparatus according to claim 1 further comprising:

a period jitter estimator to which the timing jitter sequence is inputted for calculating its differential sequence and for outputting a period jitter sequence of the signal under measurement; and

a cycle-to-cycle period jitter estimator to which the period jitter sequence is inputted for calculating its differential sequence and for outputting a cycle-to-cycle period jitter sequence to supply it to said jitter detector.

4. The jitter measurement apparatus according to any one of claims 1-3 wherein said zero-crossing timing estimator comprises:

a linear instantaneous phase data interpolator to which the linear instantaneous phase data are supplied for interpolating linear instantaneous phase data between a plurality of linear instantaneous phase data around a predetermined phase value in the linear instantaneous phase data;

zero-crossing data determination means for determining a data closest to the predetermined value in the data-interpolated linear instantaneous phase data; and

a timing estimator for estimating a timing of the determined data.

5. The jitter measurement apparatus according to any one of claims 1-3 wherein said zero-crossing timing estimator comprises:

an instantaneous phase data interpolator to which the instantaneous phase data are supplied for interpolating instantaneous phase data between a plurality of instantaneous phase data around a predetermined phase value in the instantaneous phase data;

zero-crossing data determination means for determining a data closest to the predetermined phase value in the data-interpolated instantaneous phase data; and

a timing estimator for estimating a timing of the determined data.

6. The jitter measurement apparatus according to any one of claims 1-3 wherein said zero-crossing timing estimator comprises:

a waveform data interpolator to which real part waveform data of the complex analytic signal are supplied for interpolating waveform data between a plurality of waveform data around a zero-crossing in the real part waveform data;

zero-crossing data determination means for determining a waveform data closest to the zero-crossing in the data-interpolated real signal waveform data; and

a timing estimator for estimating a timing of the determined data.

7. The jitter measurement apparatus according to any one of claims 1-3 wherein said zero-crossing timing estimator is means to which any one data group out of the linear instantaneous phase data group, the instantaneous phase data group and the real part waveform data group of the complex analytic signal is supplied for estimating a zero-crossing timing, by an inverse interpolation method, from a plurality of data around a predetermined value in the supplied data group and for outputting the zero-crossing timing.

8. The jitter measurement apparatus according to any one of claims 1-3 wherein said analytic signal transformer comprises:

a band-pass filter to which the signal under measurement is supplied for extracting only components around a fundamental frequency from the signal under measurement to limit the bandwidth of the signal under measurement; and

a Hilbert transformer for Hilbert-transforming an output signal of said band-pass filter to generate a Hilbert pair of the input signal.

9. The jitter measurement apparatus according to any one of claims 1-3 wherein said analytic signal transformer comprises:

a time domain to frequency domain transformer to which the signal under measurement is supplied for transforming the signal under measurement into a both-sided spectrum signal in frequency domain;

a bandwidth limiter for extracting only components around a positive fundamental frequency in the both-sided spectrum signal; and

a frequency domain to time domain transformer for inverse-transforming an output of said bandwidth limiter into a signal in time domain.

10. The jitter measurement apparatus according to any one of claims 1-3 further comprising a waveform clipper to which the signal under measurement is inputted for removing amplitude modulation components of the signal under measurement to supply a signal having only phase modulation components of the signal under measurement to said analytic signal transformer.

11. The jitter measurement apparatus according to any one of claims 1-3 wherein said jitter detector is a peak-to-peak detector for obtaining a difference between the maximum value and the minimum value of the supplied jitter sequence.

12. The jitter measurement apparatus according to any one of claims 1-3 wherein said jitter detector is a root mean square detector for obtaining an RMS (root mean square) value of the supplied jitter sequence.

13. The jitter measurement apparatus according to any one of claims 1-3 wherein said jitter detector is a histogram estimator for obtaining a histogram of the supplied jitter sequence.

14. A jitter measurement method comprising the steps of:

transforming a signal under measurement into a complex analytic signal;

estimating an instantaneous phase of the signal under measurement from the complex analytic signal;

estimating a linear instantaneous phase of an ideal signal that does not contain a jitter by obtaining a least mean square line of the instantaneous phase;

estimating a zero-crossing timing of the signal under measurement using any one of an interpolation method and an inverse interpolation method;

calculating a difference between an instantaneous phase value of the signal under measurement and a linear instantaneous phase value of the ideal signal at the zero-crossing timing to estimate a timing jitter sequence; and

obtaining a jitter of the signal under measurement from the jitter sequence.

15. The jitter measurement method according to claim 14 further comprising the step of:

providing the timing jitter sequence as an input for calculating its differential sequence and for outputting a period jitter sequence of the signal under measurement.

16. The jitter measurement method according to claim 14 further comprising the steps of:

providing the timing jitter sequence as an input for calculating its differential sequence and for outputting a period jitter sequence of the signal under measurement; and

providing the period jitter sequence as an input for calculating its differential sequence and for outputting a cycle-to-cycle period jitter sequence.

17. The jitter measurement method according to any one of claims 14-16 wherein said step of estimating a zero-crossing timing comprises the steps of:

interpolating linear instantaneous phase data between a plurality of linear instantaneous phase data around a predetermined phase value in the linear instantaneous phase data;

determining a data closest to the predetermined phase value in the data-interpolated linear instantaneous phase data; and

estimating a timing of the determined data.

18. The jitter measurement method according to any one of claims 14-16 wherein said step of estimating a zero-crossing timing comprises the steps of:

interpolating instantaneous phase data between a plurality of instantaneous phase data around a predetermined phase value in the instantaneous phase data;

determining a data closest to the predetermined phase value in the data-interpolated instantaneous phase data; and

estimating a timing of the determined data.

19. The jitter measurement method according to any one of claims 14-16 wherein said step of estimating a zero-crossing timing comprises the steps of:

interpolating waveform data between a plurality of waveform data around a zero-crossing in the real part waveform data of the analytic signal;

determining a waveform data closest to the zero-crossing in the data-interpolated signal waveform data; and

estimating a timing of the determined data.

20. The jitter measurement method according to any one of claims 14-16 wherein said step of estimating a zero-crossing timing is a step in which any one data group of the linear instantaneous phase data group, the instantaneous phase data group and the real part waveform data group of the complex analytic signal is inputted for estimating a zero-crossing timing, by an inverse interpolation method, from a plurality of data around a predetermined value in the inputted data group.

21. The jitter measurement method according to claim 14 wherein said step of estimating a zero-crossing timing uses a polynomial interpolation.

22. The jitter measurement method according to claim 14 wherein a cubic spline interpolation is used for said step of estimating a zero-crossing timing.

23. The jitter measurement method according to any one of claims 14-16 wherein said step of transforming the signal under measurement into an analytic signal comprises the steps of:

extracting only components around a fundamental frequency from the signal under measurement to limit the bandwidth of the signal under measurement; and

Hilbert-transforming the band-limited signal under measurement to generate a Hilbert pair of the input signal.

24. The jitter measurement method according to any one of claims 14-16 wherein said step of transforming the signal under measurement into an analytic signal comprises the steps of:

transforming the signal under measurement into a both-sided spectrum signal in frequency domain;

extracting only components around a positive fundamental frequency in the both-sided spectrum signal; and

inverse-transforming the extracted components around the positive fundamental frequency into a signal in time domain.

25. The jitter measurement method according to any one of claims 14-16 wherein said step of transforming the signal under measurement into an analytic signal comprises the steps of:

storing the signal under measurement in a buffer memory;

taking out the signal in the sequential order from said buffer memory such that the signal being taken out is partially overlapped with the signal taken out just before;

multiplying each taken out partial signal by a window function;

transforming each partial signal multiplied by the window function into a both-sided spectrum signal in frequency domain;

extracting only components around a positive fundamental frequency of the signal under measurement from the both-sided spectrum signal transformed in frequency domain;

inverse-transforming the extracted spectrum signal having components around the positive fundamental frequency into a signal in time domain; and

multiplying the signal transformed in time domain by an inverse number of the window function to obtain a band-limited analytic signal.

26. The jitter measurement method according to any one of claims 14-16 wherein said step of obtaining a jitter is a step of obtaining a difference between the maximum value and the minimum value of the jitter sequence to calculate a peak-to-peak value.

27. The jitter measurement method according to any one of claims 14-16 wherein said step of obtaining a jitter is a step of obtaining a root mean square value of the jitter sequence to calculate an RMS value.

28. The jitter measurement method according to any one of claims 14-16 wherein said step of obtaining a jitter is a step of obtaining a histogram data of the jitter sequence.