Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
1998-06-24
2001-03-13
Tse, Young T. (Department: 2734)
Pulse or digital communications
Equalizers
Automatic
C375S232000, C375S341000, C375S346000, C360S051000, C360S065000
Reexamination Certificate
active
06201832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a data detection apparatus for use in a magnetic recording/playback system; and, more particularly, to a synchronous/asynchronous data detection apparatus for use in a magnetic recording/playback system.
DESCRIPTION OF THE PRIOR ART
An analog-based recording/playback technique has long been used in a conventional magnetic recording/reproducing system such as a video cassette recorder (VCR). When images are recorded in an analog form, which is then played back by using a conventional magnetic recording/reproducing system, the image quality may be markedly deteriorated.
For example, when a conventional VCR utilizing an analog-based recording/playback technique is in a playback mode, signals distorted due to noises and jitters are directly delivered from the VCR. Moreover, if the signals are edited or other operation is performed on the signals, distortions tend to accumulate, thereby resulting in further deterioration of the played back image quality. Therefore, development of a VCR utilizing a digital-based recording/playback technique capable of overcoming the above-mentioned shortcomings of the analog VCR has been proposed.
It is well known in the art that in the recording mode of a digital VCR, an analog video and an analog audio signals which have been coded and modulated are sampled and converted into discrete quantized digital values, and then these digital values are recorded on a magnetic tape which is used by the digital VCR as a typical data storage medium.
In the playback mode of a conventional digital VCR, magnetic flux transitions are induced in a read element of a magnetic head and supplied over a path to a preamplifier as an analog signal. The preamplifier amplifies the analog signal to a predetermined level to thereby provide an analog playback signal.
And then, an analog to digital (A/D) converter of the digital VCR converts the analog playback signal at a predetermined channel rate into a digital playback signal. The digital playback signal is transmitted to a digital data processing channel of the digital VCR, wherein the digital playback signal is detected and processed.
But, in the process of digital data detection and transmission thereof, there may occur a channel-induced signal distortion, such as inter-symbol interference (ISI) due to a high speed data transmission over channels of limited bandwidth, which causes obstruction in data transmission thereof, thereby entailing transmission errors. It is well known in the art that partial response maximum likelihood (PRML) method is effective to correct ISI incurred therein.
Therefore, a conventional digital VCR usually comprises a data detection apparatus including an equalization circuit having filters to equalize a digital playback signal to an equalized signal, e.g., a partial response class
4
(PR
4
) signal. For example, a discrete time finite impulse response (FIR) filter receives and equalizes sample values of a digital playback signal to a predetermined spectrum by using a so called PRML method, wherein the discrete time transfer function for use in the PRML technique is typically (1−D
2
), wherein D represents a unit-time delay operator.
In a PRML method, the output from a noisy partial response channel is sampled at a predetermined channel rate and detected by using a PRML detector. Typically, a viterbi detector is used in a maximum likelihood sequence detection (MLSD) of the sampled partial response channel. It is well known in the art that a viterbi algorithm is an iterative process of keeping track of the path with the smallest accumulated metric leading to each state in the trellis.
In detail, the metrics of all of the paths leading to a particular state are calculated and compared in the viterbi algorithm. Then, the path with the smallest metric is selected as a survivor path. In this manner, all paths which can be part of the minimum metric paths through the trellis are stored in a path memory.
Given that the path memory is sufficiently long, all of the survivor paths will diverge from a single path within the span of the path memory. The single path from which all the current survivor paths diverge is a minimum metric path. An input sequence associated with the minimum metric path appears in all the outputs of the Viterbi detector.
The structure and function of a conventional data detection apparatus for use in a magnetic recording/playback system can be explained with reference to FIG.
1
.
FIG. 1
provides a block diagram of a same data detection apparatus
8
for use in a magnetic recording/playback system as that described in U.S. Pat. No. 5,521,945. This patent discloses a data detection apparatus including an equalization circuit having filters to equalize a digital playback signal to a PR
4
signal by employing PR
4
technique (see, FIG. 5; and column 8, line 32 to column 9, line 47 of U.S. Pat. No. 5,521,945). The data detection apparatus
8
comprises an analog to digital (A/D) converter
2
, a discrete-time FIR filter
3
, a viterbi detector
4
and a timing control circuit
5
.
In the data detection apparatus
8
, an analog playback signal is first inputted to the A/D converter
2
. The A/D converter
2
samples and converts the analog playback signal at a channel rate of 1/T into digital playback data to thereby provide discrete-time sample values of the digital playback data, wherein T is a duration of a channel symbol. And then, the FIR filter
3
equalizes the sample values to thereby supply PR
4
signals as estimated sample values to the viterbi detector
4
and the timing control circuit
5
.
The timing control circuit
5
sets a rate and phase of the sampling within the A/D converter
2
in order to synchronize a sampling clock by minimizing errors between the sample values and the estimated values based on the estimated values. The viterbi detector
4
finds the output data sequence, i.e., the estimated values closest to the received data sequence by using a known iterative algorithm. The output data sequence is fed to a post-processor for further processing thereof.
A conventional data detection apparatus such as the one described above, however, has certain limitations. First, the conventional data detection apparatus operates only in a synchronous mode, wherein the sampling rate of the A/D converter is controlled by a timing control circuit. But in some cases, it is preferable to operate the data detection apparatus in an asynchronous mode since in the asynchronous mode, a predetermined constant sampling clock signal is supplied to the A/D converter, thereby rendering the structure and control thereof simple. In short, the conventional data detection apparatus cannot realize an asynchronous mode operation thereof.
And the conventional data detection apparatus cannot utilize the output data sequence from the viterbi detector to equalize sample values in an equalization circuit such as the FIR filter
3
and to perform timing control, e.g., in the timing control circuit
5
. Therefore, the conventional data detection apparatus also has limitation in enhancing the performance of the equalization circuit and the timing control circuit.
As a result, the conventional data detection apparatus has limitations of both decreasing the transmission error rate and enhancing the data detection efficiency thereof.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a synchronous/asynchronous data detection apparatus for use in a magnetic recording/playback system.
Another object of the present invention is to provide a synchronous/asynchronous data detection apparatus for use in a magnetic recording/playback system, wherein the apparatus uses output data from a maximum likelihood sequence detection (MLSD) channel thereof in equalization process and timing control process thereof.
In accordance with the present invention, there is provided a synchronous/asynchronous data detection apparatus for use in a magnetic recording/playback system including a magnetic head having a read element
Anderson Kill & Olick PC
Daewoo Electronics Co. Ltd.
Tse Young T.
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