Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Analysis of complex waves
Reexamination Certificate
2002-04-08
2003-11-18
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Analysis of complex waves
C324S076380, C324S076150, C327S091000, C327S141000
Reexamination Certificate
active
06650101
ABSTRACT:
BACKGROUND OF THE INVENTION
Oscilloscopes and other types of equivalent-time sampling systems are used to reconstruct the waveforms of many types of optical and electrical signals. Within an equivalent-time sampling system, samples of an applied input signal are acquired by a sampler. A timebase within the equivalent-time sampling system establishes the timing of the acquired samples, so that a waveform of the input signal can be reconstructed on a display or other output device. Timing accuracy and jitter are performance parameters of the timebase that determine how accurately the waveform reconstructed by the sampling system represents the applied signal.
A first type of sampling system is shown in FIG.
1
. The timebase for this sampling system includes a programmable delay that is relied upon to establish the timing of samples acquired by a sampler relative to an applied trigger signal. As a result, performance of the sampling system is limited by the performance attributes of the programmable delay. Due to inherent noise and inaccuracies of presently available devices and elements used to implement the programmable delay, timing accuracy of the sampling system is limited to approximately four picoseconds, and jitter is limited to greater than approximately one picosecond. This low timing accuracy and high jitter prevent this type of sampling system from accurately reconstructing the waveforms of many types of applied signals, such as those present in high data-rate communication systems.
A second type of sampling system is shown in FIG.
2
. The timebase for this sampling system uses quadrature sampling of a clock signal to establish the timing of acquired samples of an applied input signal, and relies on the clock signal being synchronous with, or having an established periodic relationship with, the input signal. The quadrature sampling provides high timing accuracy (approximately 200 femtoseconds) and low jitter (approximately 100 femtoseconds). However, the sampling system is not suitable for reconstructing those portions of the input signal that do not lie within a single cycle, or period, of the clock signal.
SUMMARY OF THE INVENTION
A timebase constructed according to a first embodiment of the present invention establishes the timing of samples acquired by a signal sampler relative to a trigger signal that is synchronous with an input signal applied to the signal sampler. The timebase has high timing accuracy, low jitter, and enables portions of the applied input signal that do not lie within a single cycle, or period, of a provided reference signal to be reconstructed.
The synchronous trigger activates a first pair of samplers included in the timebase to acquire samples of a reference signal and of a shifted version of the reference signal provided within the timebase. A divider receives the reference signal and divides the frequency of the reference signal by a predesignated divisor, and a third sampler included in the timebase acquires samples of this divided reference signal, also according to the synchronous trigger. The samples of the input signal are acquired by the signal sampler according to the divided reference signal. A timing analyzer determines the timing of these acquired samples of the input signal relative to the synchronous trigger, based on the acquired samples of the reference signal, the shifted reference signal and the divided reference signal. Because the timing of the samples of the input signal is derived from the reference signal, the timebase has high timing accuracy and low jitter. In addition, the divided reference signal enables portions of the input signal that lie beyond a single period of the reference signal to be reconstructed.
In an alternative embodiment of the present invention, the timebase is implemented according to a method that determines the timing of the samples of the input signal acquired by the signal sampler.
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patent: 6401213 (2002-06-01), Jeddeloh
patent: 6434706 (2002-08-01), Jensen et al.
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Agilent Technologies, Inc. Attorney Docket No. 10010334-1—USSN 09/887,992 filed Jun. 22, 2001; Random Sampling With Phase Measurement; Inventors: Roger Lee Jungerman, Lovell H. Camnitz and Randall King.
Agilent Technologies, Inc. Attorney Docket No. 10011211-1—USSN 10/003,918 filed Nov. 1, 2001; Zero-Crossing Direction And Time Interval Jitter Measurement Apparatus Using Offset Sampling; Inventors: Lovell H. Camnitz, Roger Lee Jungerman and Randall King.
Agilent Technologies, Inc. Attorney Docket No. 10010400-1—USSN 09/919,155 filed Jul. 31, 2001; Quasi-Periodic Optical Sampling; Inventor: Roger Lee Jungerman.
Agilent Technologies, Inc. Attorney Docket No. 10011354-1—USSN 10/117,954 filed Apr. 8, 2002; Timebase For Sampling An Applied Signal Having A Synchronous Trigger; Inventors: Willard MacDonald and Roger Lee Jungerman.
Jungerman Roger Lee
MacDonald Willard
Agilent Technologie,s Inc.
Imperato John L.
Lair Donald M
Le N.
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