Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By phase
Patent
1996-06-03
1998-10-06
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By phase
327 10, 327 12, 327150, 327159, H03K 526
Patent
active
058182659
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The instant invention relates to a digital phase detector and, more particularly, to a digital phase detector for determining a phase relationship between a reference clock pulse signal and a comparison clock pulse signal and also to a method for determining this phase relationship in a phase control circuit.
A phase measuring device is known from N. Nessler, D. Fritz, "Ein digitales Issue 9, Vol. 23, pp. 319 et seq., which discloses a digital phase detector of the type mentioned at the outset.
A digital phase detector with means which generate start and stop signals from chronologically successive pulses of a reference clock and a comparison clock, and with a counter, which counts the pulses from a counting clock in the time window between a start signal and the succeeding stop signal, wherein the counter value of the counter is a measure of the phase shift between the reference clock pulse and comparison clock pulse, is known. This digital phase detector is described Stuttgart, 4th Edition, 1987, p. 46, Ill. 31/3. This phase detector has the disadvantage that very small phase differences are not detected because of quantization errors.
An analog phase detector, which delivers an output signal which has a sign, is disclosed in Tietze/Schenk "Halbleiter-Schaltungstechnik" Heidelberg, 10th Edition, 1993, pp. 962 et seq. This output signal is a rectangular pulse, whose width is proportional to the phase difference and its amplitude is negative when there is a negative phase difference.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a digital phase detector of the type mentioned at the outset, which is inexpensive and has a high phase resolution.
This object, and others which will become more important hereinafter, are attained in a digital phase detector comprising means for generating a start signal and means for generating a stop signal from respective chronologically successive pulses of a reference clock pulse signal and a comparison clock pulse signal, a counter for counting counter clock pulses of a counter clock pulse signal, advantageously having a higher frequency than that of the reference and comparison clock signals, means for turning the counter on in response to the start signal and for turning the counter off in response to the stop signal so that the counter counts the counter clock pulses during a time window between the start and stop signals to obtain a counter count which is a measure of a phase shift between the reference clock pulse signal and the comparison clock pulse signal.
According to the invention quantization errors in the phase shift are reduced by including means for obtaining phase shift sign information from the comparison clock pulse signal and the reference clock pulse signal, and means for adding a constant to the counter count and for subsequently assigning the phase shift sign information thereto to form a resulting phase shift signal.
In a preferred embodiment of the invention the means for adding the constant includes a digital input for the counter count and means for performing the adding including fixed wiring at the input that adds the constant to the counter value. Advantageously the constant is 0.5 and the means for adding the constant includes a digital input for the counter count, means for shifting k bits of the counter count at the digital input toward higher bit values and resetting a lowest bit of the k bits permanently to level "H" at the digital input.
The digital phase detector is advantageously used in a phase control circuit to considerably reduce quantization errors.
A digital phase detector which detects a phase difference between two pulses by counting the time difference existing between the two pulses by means of a counting pulse of higher frequency has quantizing errors. The accuracy of this phase detector often is not satisfactory, even with very high counting pulses. The effects of the quantizing error on the output phase of a phase control circuit are considerably reduced by means
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patent: 4264866 (1981-04-01), Benes
patent: 4506175 (1985-03-01), Reitmeier et al.
patent: 5180933 (1993-01-01), Krzyzanowski
Ein Digitales Phasenmassgerat. Nessler & Fritz, Elektronik 1974, Heft 9, pp. 319-324 no month.
Halbleiter-Schaltungegstechnik. Tietze & Schenk.
Theorie Und Anwendugen Des Phase-Locked Loops. Best no date.
Meller Wolfgang
Widmann Fritz
Callahan Timothy P.
Lam T. T.
Robert & Bosch GmbH
Striker Michael J.
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