Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
2000-02-15
2001-04-10
Young, W. R. (Department: 2651)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S053350, C369S059220
Reexamination Certificate
active
06215744
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a signal processing system for a magnetic disk device, an optical disk device or the like, and more particularly to a signal processing method and apparatus suitable for the reduction in power consumption of a circuit or LSI.
Recently, a partial response maximum likelihood (hereinafter abbreviated to PRML) decoding system is put into practice as a high-efficiency signal processing system in a magnetic disk device. The high-efficiency signal processing system means a system which can realize a desired data error rate at a low S/N.
FIG. 17
shows an example of the construction of a general magnetic disk device using a PRML signal processing system. The original data is supplied to an encoder
7
for error correction code (ECC) through an interface circuit
8
so that it is added with redundant data necessary for error correction. Next, the original data added with redundant data is subjected by a data modulator
6
to modulation necessary for the PRML system and is recorded on a magnetic disk
3
by a magnetic head
4
through a recording/reproducing amplifier
5
. A signal reproduced from the magnetic disk is passed through the recording/reproducing amplifier
5
and then PRML-processed by a data demodulator
71
. The demodulated data is error-corrected by a decoder
2
for error correction code and is thereafter converted through the interface circuit
8
into the original data. With such a recording/reproducing process, the reproduction of a low S/N signal is performed. An extended PRML (EPRML) system, an extended EPRML (EEPRML) system, a TRELLIS demodulation system and so forth are investigated as signal processing systems which make the reproduction of a lower-S/N signal possible.
On the other hand, the concept of data demodulation with connection code positioned as a superordinate concept of the signal processing system has been proposed. A known example includes “Producing Soft-Decision Information at the Output of a Class-IV Partial Response Viterbi Detector”, International Conference on Communications '91 Conference Record, Volume 2 of 3. This known system is constructed to perform the demodulation of data by combining two signal processing systems as shown in FIG.
18
. First, the data demodulator
71
is used at an initial stage to perform the demodulation of data and the extraction of information which gives the reliability of that data. The result of data demodulation at the initial stage is supplied to the next stage formed by the decoder
2
for error correction code which performs the decoding of data at a high efficiency by utilizing the data reliability information. Thus, a connection code scheme utilizing the data reliability information with the coupling thereof with the error correction code decoding system being hitherto taken into consideration is investigated as an effective system for realizing the high-efficiency signal processing system.
In the signal processing system suitable for the implementation of high efficiency and the data demodulating system using the connection code, as mentioned above, high-efficiency data demodulation is attained but an operation processing for performing data demodulation is exponentially complicated. In general, a signal processing circuit having a low data discriminating capability (for example, the PRML system) is simple in data discriminating method and small in both circuit scale and power consumption whereas a signal processing circuit having a high data discriminating capability (for example, the EPRML system or the TRELLIS system) is complicated in circuit and large in power consumption. Accordingly, a signal processing LSI for performing the data demodulation of a low-S/N signal has an increase in scale of an operating circuit and an increase in power consumption thereof. The increase in power consumption results in a substantial hindrance to the realization of a signal processing LSI.
SUMMARY OF THE INVENTION
An object of the present invention is to realize a data demodulating system suppressing an increase in power consumption which results in the largest hindrance to the LSI implementation of a high-efficiency signal processing system. More particularly, an object of the present invention is to realize a data demodulating method and system which can operate a high-efficiency signal processing system such as an EPRML system, a TRELLIS system or the like with a power consumption approximately equivalent to that in the PRML system.
In the present invention, the barometer of a data reliability proposed by a connection code scheme is utilized in respect to the reduction of a power consumption, thereby making it possible to remarkably reduce the power consumption of a signal processing circuit with a high-efficiency decoding performance being kept. Basically, this is realized by combining a first signal processing circuit having a lower data discriminating capability and a second signal processing circuit having a higher data discriminating capability, providing a reliability detecting circuit for extracting a data reliability at the time of data discrimination by the first signal processing circuit, and operating the second signal processing circuit adaptively in accordance with the extracted reliability.
In a data discriminating process of the present invention, the first signal processing circuit having a lower data discriminating capability is operated while the second signal processing circuit having a higher data discriminating capability is operated, as required. The reliability detecting circuit detects the deterioration in reliability of data discrimination by the first signal processing circuit and the second signal processing circuit starts and completes its data discriminating operation on the basis of the result of detection by the reliability detecting circuit.
In the present invention, the second signal processing circuit demodulates data for which the data discriminating performance of the first signal processing circuit is insufficient. Therefore, the overall data reproducing performance is approximately represented by the data discriminating performance of the second signal processing circuit. Regarding a power consumption, on the other hand, the operating period of the second signal processing circuit having a large power consumption is limited to only a required time. Therefore, the power consumption of the overall data demodulator is approximately determined by the first signal processing circuit.
The above object of the present invention is achieved by the data demodulating system mentioned above.
According to the present invention, a remarkable reduction in power consumption of a signal processing circuit with a high-efficiency decoding performance kept is made possible by effectively utilizing the barometer of a data reliability proposed by a connection code scheme.
A specific effect will be estimated in regard to a data demodulating system in which a switching is made between a PRML system and an EPRML system. In the case where a code error rate is about 10
−4
which may be regarded as the lower limit of a code error rate usually allowed in a magnetic disk device, the rate of a likelihood difference &Dgr;nk falling within this setting range comes to about 10
−3
. Namely, the activation of EPRML only one time for 1000 bits suffices. When an EPRML processing circuit is activated once, the processing is performed for a period of about 50 bits. The operation rate of the EPRML processing circuit results in about {fraction (1/100)} and a power consumption is correspondingly reduced.
As compared with the PRML system, the EPRML system has an estimated improvement of S/N equal to or greater than about 2 dB in the case where the ratio of the half band width of the reversal of regenerative isolated magnetization of a magnetic recording device to the half band width of a record signal is about 2.5 falling within a range in which the device is put into practice. Accordingly, when the above processing is performed, the effect o
Mita Seiichi
Satoh Naoki
Takashi Terumi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Young W. R.
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