Pulse or digital communications – Synchronizers
Patent
1995-08-09
1998-11-17
Tse, Young T.
Pulse or digital communications
Synchronizers
375371, H04L 702
Patent
active
058387439
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a system for serial reception or reading of information, and especially a system for receiving or reading digital information, in which the local clock is not slaved to the send clock (or write clock) and in which it is required to determine the phase of the signal with respect to the local clock.
The receiving portion of a pathway for transmitting or storing digital information generally includes a function of regenerating the clock for the transmitted information. In most cases this clock is reconstructed from the actual string of data transmitted. The present invention applies to the reconstruction of the clock of a received signal sampled asynchronously with respect to this clock.
A phase tracking filter embodied digitally includes a phase (or phase deviation) measurement function and a prediction (or estimation) function.
When the analog signal is sampled on the basis of the reconstructed clock, as is generally the case in digital pathways, the phase deviation is close to zero once the phase loop is locked. It is obvious how to determine the phase error if the signal is oversampled by a factor of two. Algorithms (Mueller and Muller) have been proposed in the case of a binary signal sampled at bit frequency.
In the case where the sampling frequency is arbitrary with respect to the bit frequency, the instantaneous phase varies rapidly and it is not obvious how to determine this phase with good accuracy.
SUMMARY OF THE INVENTION
The circuit which is the subject of the invention makes it possible to determine the phase of each of the samples of a two-level or multilevel digital signal transmitted through an analog channel.
The invention therefore relates to a system for receiving or reading digital serial information, in which the information is sampled at regular intervals under the control of a local clock, characterized in that it includes at least one table containing for each pair of values of consecutive information samples a measured phase value.
BRIEF DESCRIPTION OF THE DRAWINGS
The various subjects and characteristics of the invention will emerge more clearly in the description which will follow given by way of example and in the appended figures which represent:
FIG. 1, an example of a received signal;
FIG. 2, a representation of the loci of sample pairs;
FIGS. 3a and 3b, an example of the principle of the phase measurement;
FIGS. 4 and 5, other loci of sample pairs;
FIG. 6, a diagram explaining the determination of the likely position of a sample pair;
FIG. 7, a simplified filter of the phase shift measurement;
FIG. 8, a more complete filter of the phase shift measurement;
FIG. 9, an amplitude monitoring filter;
FIGS. 10 and 11, a general system of phase shift measurement; and
FIGS. 12a-12c, representations of loci of the sample pair at different frequencies.
DISCUSSION OF THE PREFERRED EMBODIMENTS
The system of the invention will firstly be described in a simple and then a generalized case.
FIG. 1 represents a binary signal transmitted through a Nyquist channel and sampled at a frequency f.sub.e =2 f.sub.b (f.sub.b =bit frequency or binary frequency of the signal received).
The geometrical representation of the locus of the successive sample pairs (z.sub.k-1, z.sub.k) with a nominal amplitude and in the absence of noise is given in FIG. 2. The various trajectories can be graduated in phase. It can be seen that when the point representing the signal lies in one of quadrants 2 or 4 of the (z.sub.k-1, z.sub.k) plane, it is possible to determine unambiguously the phase of the signal at this instant. For example, samples E1 and E2 of FIG. 1 give rise to a point in quadrant 2.
In the absence of noise, other regions of the possible trajectories are usable. On the other hand, when the representative point lies close to the point (1, 1) or the point (-1, -1), it is not possible to give a value of the phase of the signal.
In quadrants 1 and 3, the right-hand portions correspond to sample pairs such as E3-E4, situate
REFERENCES:
patent: 4030045 (1977-06-01), Clark
patent: 4607230 (1986-08-01), Kaku et al.
patent: 4807257 (1989-02-01), Schouhamer Immink et al.
patent: 4908842 (1990-03-01), Collins
Audoin Michel
Colineau Joseph
"Thomson-CSF"
Tse Young T.
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