Internally triggered equivalent-time sampling system for...

Coded data generation or conversion – Analog to or from digital conversion – Analog to digital conversion

Reexamination Certificate

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C341S061000

Reexamination Certificate

active

06181267

ABSTRACT:

BACKGROUND OF THE INVENTION
Equivalent-time sampling systems are used to characterize and display high-speed data signals. An equivalent-time sampling system disclosed by Agoston in U.S. Pat. No. 4,812,769 relies on a trigger signal that is synchronous with the data signal to provide trigger events used for acquiring samples of the data signal. The timing of the acquired samples is progressively varied relative to the trigger events until the number of samples is sufficient to reconstruct the waveform of the data signal on a display. However, a synchronous trigger signal may not be available in optical fiber networks or other communication networks, making it difficult to characterize high-speed data signals within these networks using this type of equivalent-time sampling system. In U.S. Pat. No. 4,678,345, Agoston discloses an equivalent-time pseudorandom sampling system that does not rely on a synchronous trigger signal. Trigger events in this system are provided by the data signal. Time intervals between the trigger events on the data signal establish the relative timing of acquired samples. It is difficult to isolate characteristics of the data signal such as jitter or other timing instabilities using this type of sampling system since timing of sample acquisitions is derived directly from the data signal itself. For example, jitter in the data signal may be masked or enhanced by the equivalent-time pseudorandom sampling system, depending on how the system processes the trigger events. Accordingly, there is a need for a sampling system capable of characterizing a high-speed data signal that does not rely on a synchronous trigger signal and that does not derive the timing of sample acquisitions directly from the data signal.
SUMMARY OF THE INVENTION
According to the preferred embodiment of the present invention, an internally triggered equivalent-time sampling system characterizes high-speed data signals having a predetermined nominal data rate by using an internal oscillator that runs independent of a synchronous trigger signal. The sampling system acquires samples of the data signal at a strobe rate, set by the oscillator, which is lower than the nominal data rate of the data signal. The samples, the strobe rate, and the nominal data rate are communicated to a quality optimizer which compensates for static rate deviations between the nominal data rate and the actual data rate of the data signal to establish timing correspondence between the acquired samples. The timing correspondence establishes the time placement of the acquired samples when characterizing the data signal on a display or other output device. When the oscillator has high timing stability relative to the data signal, jitter and other timing instabilities of the data signal are isolated so that attributes of the data signal are accurately characterized by the sampling system.


REFERENCES:
patent: 4678345 (1987-07-01), Agoston
patent: 4812769 (1989-03-01), Agoston
patent: 5315627 (1994-05-01), Draving
patent: 5631553 (1997-05-01), Bose et al.
patent: 5684837 (1997-11-01), Chen

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