Coded data generation or conversion – Phase or time of phase change
Reexamination Certificate
2001-10-26
2002-11-12
Young, Brian (Department: 2819)
Coded data generation or conversion
Phase or time of phase change
Reexamination Certificate
active
06480126
ABSTRACT:
THE FIELD OF THE INVENTION
This invention relates generally to systems and methods for digitizing the phase of an analog signal. This invention relates more particularly to a system and method for continuously and accurately digitizing the cumulative phase progression of a quasi-sinusoidal signal based on digital samples of its waveform.
BACKGROUND OF THE INVENTION
Many existing phase detectors are analog in nature and have a limited dynamic range. Generally, such phase detectors generate an output voltage indicative of the phase difference between two oscillations that are close in frequency. The polarity of the output voltage indicates which oscillation is leading the other. The magnitude of the output voltage tends to be proportional to the phase difference. The dynamic range of such phase detectors is typically limited to one cycle in each direction. Digital phase detection is typically preferred for phase detection of dynamic ranges wider than 1 or 2 cycles.
A prior method of digitizing phase that has very wide dynamic range is described in U.S. Pat. No. 5,663,666, entitled DIGITAL PHASE DETECTOR, by Chu and Sommer. Such a method can be used only on a signal operating within a very narrow frequency band, 100 ppm for example, such as a signal from a crystal oscillator.
Another prior method of phase digitizing involves time-stamping the zero-crossings of the signal, as described in “Phase Digitizing Sharpens Timing Measurements,” David Chu, IEEE Spectrum, July 1988, pp. 28-32. For precise results, such methods usually involve custom time-digitizer circuits, such as described in U.S. Pat. No. 5,166,959, entitled PICOSECOND EVENT TIMER, by Chu and Knotts. Phase digitizing techniques that involve time-stamping the zero-crossings of a signal are better suited for agile signals of high frequencies, where signal frequencies may change radically and suddenly, and many zero-crossings are available to generate time-stamp data. A penalty for such a wide-band approach is noise.
In an interferometer arrangement, noise is usually generated from fluctuating beam alignment, turbulence, photo-diodes, electronic amplification and from the light source itself. In noisy environments, unexpected spurious zero-crossings may occur due to multiple triggering of the same signal edge, causing a catastrophic failure in previous phase digitizing processes.
In metrology of moving objects, the signals are generally quasi-sinusoidal and of limited agility due to the physical inertia of objects being monitored. Frequency is proportional to the velocity of the object being monitored, and phase is proportional to the distance of travel. Because physical objects cannot instantaneously jump from one velocity to a much different velocity, the frequency of the signals changes relatively slowly.
The frequency of the signal, although changing slowly, may traverse a wide range, including very low frequencies where the number of zero-crossings available for measurement may be at a premium. Also, the occurrences of zero-crossings are generally non-uniform. This non-uniformity may pose additional difficulty in ascertaining the “data age”—the time between event occurrence and the presentation of its measurement data. These factors render the zero-crossing approach not an optimum technique for phase digitizing for interferometry.
It would be desirable to provide a phase digitizing system and method that employs digital signal processing for continuously generating digital phase data representing the phase of an incoming analog signal, without the disadvantages of previous phase digitizing techniques.
SUMMARY OF THE INVENTION
One form of the present invention provides a method of digitizing characteristic parameters of a quasi-sinusoidal analog signal of unknown magnitude, frequency and phase-offset. The analog signal is digitized at a first sampling rate, thereby generating a plurality of sets of digital signal waveform samples. Successive sets of the digital signal waveform samples are digitally processed to generate continually updated digital characteristic parameters representing a characteristic behavior of the quasi-sinusoidal analog signal.
REFERENCES:
patent: 6049297 (2000-04-01), Ducharme
Agilent Technologie,s Inc.
Young Brian
LandOfFree
Phase digitizer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Phase digitizer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Phase digitizer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2961230