Dynamic information storage or retrieval – Binary pulse train information signal
Reexamination Certificate
2000-10-27
2002-05-14
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
C369S059120, C369S124010, C369S044340
Reexamination Certificate
active
06388969
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority from prior French Patent Application No. 99-13524, filed Oct. 28, 1999, the entire disclosure of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electronic circuits, and more specifically to an electronic device for calculating the mutual phase shift of two sampled incident signals.
2. Description of Related Art
Digital discs are commonly used to store large amounts of data for distribution. Current examples of optical digital discs include “compact discs” such as the CD-ROM (Read Only Memory Compact Disc) and multifunction digital discs such as the DVD (Digital Versatile Disc), which typically stores data (e.g., image data) in a compressed state. When reading from an optical digital disc, the phase shift between two sampled incident signals corresponds to the positioning error of the incident optical beam (e.g., laser spot) that is illuminating the track of the digital disc that is being read.
Conventional devices that read digital discs detect any phase shift between two sampled incident signals emanating from photodetectors to determine the positioning error of the incident optical beam. This positioning error is then used in a slaving loop to modify the incident optical system so as to bring the optical beam back to the track and slave it thereto. Conventionally, the determination of the mutual phase shift between two sampled incident signals requires the use of several memories of the “first-in, first-out” (FIFO) type to store a number of samples of the received signals in succession, and a relatively complex control system to make it possible to tag the time instants of appearance of the transitions.
SUMMARY OF THE INVENTION
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a simple device for calculating the mutual phase shift of two sampled incident signals.
Another embodiment of the present invention provides an electronic device for calculating the mutual phase shift of two sampled incident signals.
Yet another object of the present invention is to provide a digital disc reader having circuitry for calculating the mutual phase shift of two sampled incident signals.
One embodiment of the present invention provides a device for calculating mutual phase shift of first and second incident signals. The device includes a first pair of blocks associated with the first incident signal, a second pair of blocks associated with the second incident signal, checking means, and post-processing means. Each of the blocks has storage elements for storing a predetermined set of samples of the corresponding incident signal. In the presence of minimum samples or maximum samples of both incident signals, the checking means stores a first set of samples relating to the first incident signal in one of the blocks of the first pair and a first set of samples relating to the second incident signal in the counterpart block of the second pair, and then stores the following sets of samples of each incident signal alternately in the two blocks of each pair. The checking means delivers a block validation signal when a set of samples has been completely stored in the storage elements of one of the blocks. Further, the post-processing means determines the phase shift of the first and second incident signals when two block validation signals are delivered for two counterpart blocks of the two pairs, on the basis of the content of the two counterpart blocks. In a preferred embodiment, the predetermined set of samples includes at least one minimum sample, one maximum sample, and two intermediate samples that are representative of a transition of the incident signal with respect to a predetermined overstepping threshold.
Another embodiment of the present invention provides a digital disc reader that includes an optical head having a light emitter and a plurality of photodetectors, means for pairwise summing signals emanating from the photodetectors and outputting first and second sampled incident signals, and a device for calculating mutual phase shift of the first and second incident signals.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.
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Chelal Rabah
Lebowsky Fritz
Marrec Sonia
Bongini Stephen
Edun Muhammad
Fleit Kain Gibbons Gutman & Bongini P.L.
Jorgenson Lisa K.
STMicroelectronics S.A.
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