Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2002-05-16
2004-12-14
Nghiem, Michael (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
Reexamination Certificate
active
06832172
ABSTRACT:
FIELD OF THE INVENTION OF THE INVENTION
The subject invention generally concerns the field of jitter measurement, and in particular concerns an apparatus and method for measuring jitter in a signal under test with a real time digital storage oscilloscope.
BACKGROUND OF THE INVENTION
Jitter is a well-known term of art used to define the deviation from an ideal timing of an event in a signal. Jitter results in the mispositioning of the significant edges in a sequence of data bits from their ideal positions. In modern serial data communications systems, the serial data clock is not usually transmitted with the data, so jitter could cause data errors at the receiving end. It is therefore extremely important to determine the amount and kind of jitter that may be present in a signal under test. In this regard, it is noted that jitter comprises two distinct types, deterministic jitter (DJ) and random jitter (RJ). Random jitter (RJ) is unbounded in amplitude and assumed to be Gaussian. In contrast, deterministic jitter is not random and is bounded in amplitude, and comprises Intersymbol Interference (ISI), Duty Cycle Distortion (DCD), and Periodic Jitter (PJ). Note that Intersymbol Interference (ISI) is also known in the art as Data Dependent Jitter (DDJ).
ISI is data-dependent deterministic jitter caused by the time differences required for a signal to arrive at a receiver threshold when starting from different places in bit sequences (i.e., symbols). DCD is the difference in the mean pulse width of a logic “1” pulse compared to the mean pulse width of a logic “0” pulse in a clock-like bit sequence. PJ is characterized by periodic variations in edge transition times at frequencies that are uncorrelated with the data rate. The signed difference between the measured time location of each sequential data symbol transition and the nominal symbol transition time is called the Time Interval Error (TIE).
RJ and DJ accumulate differently in a serial data communication link. If the parameters that characterize each of the two categories of jitter are available, then bit error rate (BER) can be estimated. It is therefore desirable to be able to measure each of the two categories of jitter. Unfortunately, one cannot simply choose to measure one of the two categories of jitter because both categories are always mixed together and appear as “total jitter”. One must separate the two categories prior to estimating their parameters.
U.S. Pat. No. 6,356,850 B1(Wistrup, et al.) discloses a jitter separation and parameter estimation apparatus and method which is based on a Time Interval Analyzer (TIA) using an arming system. Unfortunately, a TIA with an arming system does not lend itself to incorporation in an oscilloscope without that arming system. Thus, existing oscilloscopes are capable of showing only total jitter. What is needed is a solution to the problem of measuring RJ and DJ with an oscilloscope.
SUMMARY OF THE INVENTION
A jitter separation apparatus and method, based on spectrum analysis, separates deterministic jitter and random jitter using their spectral properties. Deterministic jitter exhibits a spectrum of impulses, whereas random jitter exhibits a broad, flat spectrum. A time domain histogram and a frequency domain histogram of the signal are investigated to obtain jitter components. Bit error rate estimation is performed based on the jitter separation result.
REFERENCES:
patent: 6356850 (2002-03-01), Wilstrup
patent: 2001/0044704 (2001-11-01), Li et al.
patent: WO 99 39216 (1999-08-01), None
Mike P. Li, et al., “A New Method for Jitter Decomposition Through Its Distribution Tail Fitting”, ITC International Test Conference, Wavecrest Corporation, pp. 788-794, Issue No. 0-7803-6753-1/99, Copyight 1999 IEEE.
Li, et al. “A New Method for Jitter Decomposition Through It's Distribution Tail Fitting”:, Proceedings International Test Conference 1999, ITC 99, Atlantic City, N.J., Sep. 28-30, 1999. International Test Conference, New York, NY. IEEE, US, vol. Conf. 30, Sep. 28, 1999, pp. 788-794, XP002140775. ISBN: 0-7803-5754-X.
Farhang-Boroujeny B. et al., “Nyquist Filters With Robust Performance Against Timing Jitter”, IEEE Transactions on Signal Processing, Dec. 1998, IEEE, USA vol. 46, No. 12, pp. 3427-3431, XP002244699. ISBN: 1053-587X.
Pereira, Jorge M. N. et al, “Inherent-Jitter Effects In The New Rapid Acquisition Method For Frequency -Hopped Push-To-Talk Spread Spectrum Systems: A Jitter-Fighting Scheme,”, Effects of Electromagnetic Noise and Interference on Performance of Military Radio Communication Systems (AGARD-CP-4230), Lisbon, Portugal, Oct. 26-30, 1987, pp. 23/1-20, XP008016467 1988, Neuilly Sur Seine, France, AGARD, France.
Guenther Mark L.
Tan Kan
Ward Benjamin A.
Gray Francis I.
Lenihan Thomas F.
Nghiem Michael
Tektronix Inc.
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