Pulse or digital communications – Receivers – Particular pulse demodulator or detector
Reexamination Certificate
1999-08-12
2002-09-03
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Receivers
Particular pulse demodulator or detector
C375S229000, C375S290000, C714S795000, C360S039000
Reexamination Certificate
active
06445754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a playback data detecting device which is suitable for a digital optical disk storage device, hard disk storage device, and digital VTR and, in particular, to a playback data detecting device which is operable to playback data constraining the number of continuous non-inverse bits to at least “2”.
2. Description of the Related Art
Generally, in a digital optical disk storage device, hard disk storage device, or digital VTR, a threshold voltage level is determined for discriminating digital playback data. And when a playback voltage level of a bit of the digital playback data exceeds the threshold voltage level, the bit is discriminated as a high level “H”, and, otherwise, the bit is discriminated as a low level “L”. Such a technique makes use of characteristics of digital recording, and the technique can be done by a simple circuit because a logic for the discrimination is simple. However, whenever the playback voltage level of a bit which is to be discriminated as a low level slightly exceeds the threshold voltage level due to error, a bit error occurs. Also, when once such a bit error occurs, it is not possible to correct the error at a discriminate/playback block.
For this reason, in a part of a digital optical disk apparatus, a detecting method has been adopted which combines a method known as a partial response (
1
,
1
) with three levels and a Viterbi decoding method of two states.
When a signal is recorded on the apparatus, the method converts the signal into a NRZ (non return to zero recording) signal or a NRZI (nonireturn to zero inverted recording) signal using a pre-coder. On the other hand, when playback of the signal is executed, the method detects the signal using the partial response (
1
,
1
). The detecting method by the use of the partial response (
1
,
1
) carries out data detection using the correlation between playback signals. In the method, when a recording signal “1” is given, playback signals “..001100..” are obtained and level detection of three levels is consequently made.
After the detection due to the partial response (
1
,
1
) is finished, a Viterbi decoding method of three levels and two states is executed. The Viterbi decoding method, taking two playback states, such as state S
0
and state S
1
, makes a transition to state S
0
and provides the value of the output signal “0” when the signal of “−1” is input in the state S
0
. When the signal of “0” is input in the state S
0
, it makes a transition to state S
1
and provides the value of the output signal “1”. When the signal,of “0” is input in the state S
1
, it makes a transition to state S
0
and provides the value of the output signal “1”. When the signal of “1” is input in the state S
1
, it makes a transition to state S
1
and provides the value of the output signal “0”. When the signal violating the above-described state transition rules is inputted, bit error correction is performed by detecting an incorrect state and judging an original state. As a result, the error rate for random errors is improved.
In the above-mentioned method which carries out equalization using the partial response (
1
,
1
) and decoding using the three levels and the Viterbi decoding method of two states, detecting of playback data is performed by bit error correction based on the correlation between the three levels which is provided by the partial response (
1
,
1
). However, when a recording side records data by converting the same into signals which have a minimum inverse metric or interval at least two, namely, the number of continuous non-inverse bits equal to at least “2”, the feature of the signals may not be fully utilized. More specifically, it is to be noted that a bit sequence includes at least two continuous signals of “0” or “1” and, as a result, non-inverse bits lasts for at least two bits.
Then, the present inventor has already proposed, in Japanese Laying-Open Publication No. H06-267203(namely, 267203/1994), a playback data detecting device which is operable to perform bit error correction by making use of the above-mentioned feature of the signals. The device is used to record the signals, such as (
1
,
7
) signals which has the continuous non-inverse bits of at least “2”. The decoding method used in the device, taking four playback states as state S
0
through state S
3
. In this event, the decoding method makes a transition to state S
0
and provides the value of the output signal “0” when the signal of “−1” is input in the state S
0
. Likewise, when the signal of “0” is input in the state S
0
, it makes a transition to state S
1
and provides the value of the output signal “1”. When the signal of “1” is input in the state S
1
, it makes a transition to state S
2
and provides the value of the output signal “0”. When the signal of “1” is input in the state S
2
, it makes a transition to state S
2
and provides the value of the output signal “0”. When the signal of “0” is input in the state S
2
, it makes a transition to state S
3
and provides the value of the output signal “1”. We the signal “0”. “−1” is input in the state S
3
, it makes a transition to state S
0
and provides the value of the output signal “0”. When the signal violating the above-described state transition rules is inputted, bit error correction is performed by detecting an incorrect state and judging an original state. As a result, the error rate for random errors is improved. Thus, it might be said that the above-mentioned method is equivalent to a combination of the equalization of partial response (
1
,
1
)+a Viterbi decoding method of three levels and four states.
With the playback data device using the combination of the equalization of partial response (
1
,
1
)+the Viterbi decoding method of three levels and four states, the feature of the signals can be almost used. However, the feature is not still used completely, because only three levels of information are utilized about information included in the playback signals. Therefore, the device can be further improved.
Then, the present inventor further proposes, in Japanese Laying-Open Publication No. H05-334811 (namely, 334811/1993), the playback data detecting device which can make use of information in the playback signals more effectively. The device is also used to record signals which have the number of continuous non-inverse bits equal to at least two. The decoding method used in the device produces playback. And the decoding method, taking four playback states such as state S
0
through state S
3
, makes a transition to state S
0
and provides the value of the output signal “0” when the three levels of “−1” and the two levels of “−1” are input in the state S
0
. When the three levels of “0” and the two levels of “1” are input in the state S
0
, this makes a transition to state S
1
and provides the value of the output signal “1”. When the three levels of “1” and the two levels of “1” are input in the state S
1
, it makes a transition to state S
2
and provides the value of the output signal “0”. When the three levels of “1” and the two levels of “1” are input in the state S
2
, it makes a transition to state S
2
and provides the value of the output signal “0”. When the three levels of “0” and the two levels of “−1” are input in the state S
2
, it makes a transition to state S
3
and provides the value of the output signal “1”. When the three levels of “−1” and two levels of “−1” are input in the state S
3
, it makes a transition to state S
0
and provides the value of the output signal “0”. When the signal violating the above-described state transition rules is inputted, bit error correction is performed by detecting an incorrect state and judging an original state. As a result, the error rate for random errors is improved. Therefore, the method is a combination of equalization of partial response (
1
,
1
) with a Viterbi decoding method of three levels/two levels and four states.
In the above-mentioned decoding me
Corrielus Jean
McGinn & Gibb PLLC
NEC Corporation
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