Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1998-03-13
2001-08-21
Pham, Chi (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C708S290000
Reexamination Certificate
active
06278747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method and apparatus for data processing in general, and in particular to a method and apparatus for data detection. Still more particularly, the present invention relates to a method and apparatus for performing digital detection of data stored on an optical medium.
2. Description of the Prior Art
Binary data are typically encoded and stored on optical media as a series of optical modulations. A retrieval of these stored data requires a synchronous clock from a self-clocking analog signal waveform and a detect-and-decode system in a read channel to reconstruct the original binary data. An important element within the read channel is a waveform detector. The waveform detector may be a transition detector (commonly known as a zero-crossing detector) or a peak detector. Generally speaking, transition detectors are utilized for detecting data in Pulse-Width Modulation (PWM) recordings and peak detectors are utilized for detecting data in Pulse-Position Modulation (PPM) recordings.
Digital waveform detectors typically rely on discrete-signal embodiments of well-known analog detection techniques. In essence, an analog signal waveform is initially sampled and then digitized. The digitized samples are subsequently processed digitally to attenuate any unwanted frequency components in order to reconstruct the synchronous clock and data.
One of the more commonly known digital waveform detectors for the detection of data stored on optical disks is called an asynchronous digital waveform detector. The asynchronous digital waveform detector utilizes a straight-line approximation to estimate the location of a detection event—either a peak for PPM recordings or a transition for PWM recordings. This method works well as long as the sample rate is greater than five samples per sinusoid, where a sinusoid describes the highest frequency tone that can be written on optical storage media. Although this sample rate is not considered to be very high, there are at least two reasons why it is desirable to lower the sample rate even further. First, the design of digital circuits will be easier and the power consumption of the entire digital module will be lower if the speed at which the digital logic is required to operate is decreased. Second, under some circumstances, the number of synthesizers can be reduced from two to one, making the digital module count lower and the electronics footprint smaller, which translates to a lower total cost. As the sample rate becomes lower, however, the estimated location of a detection event obtained by straight-line approximation becomes less accurate. For example, as shown in
FIG. 9
a
, an estimate sample at location
93
obtained by a straight-line approximation of actual received samples
91
and
92
, does not coincide with actual peak location
94
of an analog signal waveform
95
from a PPM recording. Consequently, it would be desirable to provide an improved method for performing digital detection for data stored on an optical medium at a relatively low sampling rate, without sacrificing detection accuracy.
SUMMARY OF THE INVENTION
In view of the foregoing, it is therefore an object of the present invention to provide an improved method and apparatus for data processing.
It is another object of the present invention to provide an improved method and apparatus for data detection.
It is yet another object of the present invention to provide an improved method and apparatus for performing digital detection of data stored on an optical medium.
In accordance with a method and system of the present invention, a recording medium, such as an optical or magnetic medium, is initially sensed by a transducer to produce an analog data signal waveform. The analog data signal waveform is then digitized by an analog-to-digital convertor to produce a set of digitized data samples. The set of digitized data samples may be equalized to reduce noise. Subsequently, a mid-point sample is inserted between each two samples within the set of equalized data samples utilizing a mid-point interpolation algorithm. With the additional points provided by mid-point interpolation, the absence or presence of a detection event, such as a peak or a transition, between every two samples within the set of equalized data samples are determined.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
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Hutchins Robert Allen
Jaquette Glen Alan
Tsuruta Kazuhiro
Bracewell & Patterson L.L.P.
Corrielus Jean
International Business Machines - Corporation
Pham Chi
Sullivan Robert M.
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