Jitter measurement apparatus and its method

• US 6,525,523 B1
• Filed: 11/24/2000
• Issued: 02/25/2003
• Est. Priority Date: 11/24/2000
• 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): Le, N.
• Assistant Examiner(s): LEROUX, ETIENNE PIERRE
• Application Number:
  US09/722,167
• Time in Patent Office: 823 Days
• Field of Search: 324/76.39, 324/76.41, 324/76.52, 324/76.77, 375/224, 375/226, 375/371, 375/375
• US Class Current: 324/76.77
• CPC Class Codes: G01R 29/26 Measuring noise figure; Measuring signal-to-noise ratio
• CPC Class Codes: H04L 1/205 jitter monitoring

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 zero-crossing timing sequence of the signal under measurement is estimated using the instantaneous phase. An instantaneous period sequence of the signal under measurement is estimated from the zero-crossing timing sequence to obtain a jitter of the signal under measurement from the instantaneous period 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 zero-crossing timing estimator for obtaining a zero-crossing timing sequence of the signal under measurement from the estimated instantaneous phase;

a period estimator for obtaining an instantaneous period sequence of the signal under measurement from the zero-crossing timing sequence estimated by said zero-crossing timing estimator; and

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

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

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

3. The jitter measurement apparatus according to claim 1 or 2 wherein said zero-crossing timing estimator comprises:

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

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.

4. The jitter measurement apparatus according to claim 1 or 2 wherein said zero-crossing timing estimator is means to which the instantaneous phase data are supplied for estimating a zero-crossing timing sequence using an inverse interpolation from a plurality of instantaneous phase data around predetermined values in the supplied instantaneous phases to output the zero-crossing timing sequence.

5. The jitter measurement apparatus according to claim 1 or 2 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.

6. The jitter measurement apparatus according to claim 1 or 2 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.

7. The jitter measurement apparatus according to claim 1 or 2 further comprising a waveform clipper to which the signal under measurement is inputted for removing amplitude modulation components of the signal under measurement to extract only phase modulation components of the signal under measurement and to output the extracted phase modulation components to said analytic signal transformer.

8. The jitter measurement apparatus according to claim 1 or 2 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 sequence.

9. The jitter measurement apparatus according to claim 1 or 2 wherein said jitter detector is a root mean square detector for obtaining an RMS (root mean square) value of the supplied sequence.

10. The jitter measurement apparatus according to claim 1 or 2 wherein said jitter detector is a histogram estimator for obtaining a histogram of the supplied sequence.

11. 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 zero-crossing timing sequence of the signal under measurement from the instantaneous phase;

estimating an instantaneous period sequence of the signal under measurement from the zero-crossing timing sequence; and

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

12. The jitter measurement method according to claim 11 further comprising the step of:

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

13. The jitter measurement method according to claim 12 wherein said step of obtaining a jitter is a step of obtaining a root mean square value of the cycle-to-cycle period jitter sequence to calculate an RMS value.

14. The jitter measurement method according to claim 11 or 12 wherein said step of estimating a zero-crossing timing sequence comprises the steps of:

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

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

estimating a timing of the determined data.

15. The jitter measurement method according to claim 14 wherein said step of interpolating data around the predetermined value is a step of interpolating using a polynomial interpolation.

16. The jitter measurement method according to claim 14 wherein said step of interpolating data around the predetermined value is a step of interpolating data around the zero-crossing of the instantaneous phase using a cubic spline interpolation.

17. The jitter measurement method according to claim 11 or 12 wherein said step of estimating a zero-crossing timing sequence is a step of inputting the instantaneous phases and estimating a zero-crossing timing sequence using an inverse interpolation from a plurality of instantaneous phase data around predetermined values in the inputted instantaneous phases.

18. The jitter measurement method according to claim 17 wherein the inverse interpolation is an inverse linear interpolation.

19. The jitter measurement method according to claim 11 or 12 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.

20. The jitter measurement method according to claim 11 or 12 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.

21. The jitter measurement method according to claim 11 or 12 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 only 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.

22. The jitter measurement method according to claim 11 or 12 wherein said step of obtaining a jitter is a step of obtaining a difference between the maximum value and the minimum value of the sequence to calculate a peak-to-peak value.

23. The jitter measurement method according to claim 11 or 12 wherein said step of obtaining a jitter is a step of obtaining a standard deviation of the instantaneous period sequence to calculate an RMS value.

24. The jitter measurement method according to claim 11 or 12 wherein said step of obtaining a jitter is a step of obtaining a histogram data of the sequence.