Dynamic magnetic information storage or retrieval – Modulating or demodulating
Reexamination Certificate
2002-08-09
2004-05-04
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Modulating or demodulating
C360S046000, C360S031000
Reexamination Certificate
active
06731441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an information recording and reproducing apparatus, and more particular to a signal processing method, a signal processing circuit and a signal processing apparatus and a signal modulating/demodulating method and a modulating/demodulating apparatus for use in an information recording and reproducing apparatus such as a magnetic disk apparatus.
2. Description of the Prior Art
For signal processing in a magnetic recording and reproducing apparatus such as a magnetic disk apparatus, a partial response maximum likelihood decoding (PRML) system is used. The PRML system is a combination of a partial response PR system and a maximum likelihood (ML) decoding method. The PR system is a technique which allows limitation of the band of codes by positively utilizing interference between adjoining signals. Since the PR system gives rise to correlations between signals, the ML decoding method makes possible decoding on a sequence-by-sequence basis by utilizing the correlations.
FIG. 2
shows the configuration of a magnetic disk apparatus using the conventional PRML system, and
FIG. 3
, a write current waveform and a reproduction waveform by the conventional PRML system.
Referring to
FIG. 2
, on the recording side, write data
101
are encoded into an error correcting code signal by an error correcting code generator
111
. The error correcting code signal
112
is run length limited-encoded (RLL-encoded) by an error correcting code signal generator
113
, and a RLL code
114
is thereby generated. A read auxiliary signal generator
12
consists of a preamble signal generator
121
and a synchronizing signal generator
123
, and the preamble signal generator
121
generates a preamble signal
122
having data clock information and amplitude compensating information. The synchronizing signal generator
123
generates a synchronizing signal
124
containing read clock information. The RLL code
114
, the preamble signal
122
and the synchronizing signal
124
are arranged by a signal arrangement circuit
125
into a sequence fitting a format.
A write compensation circuit
131
generates a compensated write signal
132
having undergone compensation for the component of distortion to which the signal is subjected on a recording medium, and the signal is amplified by a write amplifier
133
. A write head
135
, which is a magnetic head, writes information on a recording medium
103
on the basis of a write current waveform
134
. The write current waveform manifested by the recording signal
134
will be described afterward with reference to FIG.
3
.
Then, on the reproducing side, information written on the recording medium
103
is read by a read head
151
to obtain a read current signal
152
. A read amplifier
153
amplifies the read current signal
152
, and delivers it to an equalizer
163
via a read compensation circuit
161
. Here, a read auxiliary circuit
165
extracts the preamble signal
122
and the synchronizing signal
124
. It further extracts read clock information from the synchronizing signal
124
, and extracts data clock information
167
and compensated amplitude information
167
from the preamble signal
122
.
By utilizing these read auxiliary signals, the equalizer
163
supplies an equalized signal
164
whose waveform is shaped to desired partial response characteristics. This equalized signal
164
is entered into an ML decoder
171
, which delivers a partial response signal
170
. A RLL coder
181
acquires an RLL signal
182
from the partial response signal
170
. An error correcting code decoder
183
corrects any error in the RLL signal
182
to acquire read data
102
.
Next will be described the write current waveform
134
and the read current signal
152
of the PRML system with reference to FIG.
3
. In a conventional recording system, such as the PRML system, information is determined by whether or not the amplitude of the write current waveform
134
is inverted according to the recording bit that is entered. When “1” is entered, the current waveform is inverted (
191
), or when “0” is entered, the state before its entry is maintained, and the current waveform is not inverted (
192
). If “1” is consecutively recorded (
194
), the current waveform will be inverted in every bit period, and the inverting intervals of the write current will be minimized (
193
). The value that this write current waveform
134
can take is either one of positive and negative levels (±1), and the amperage varies in every bit period. Therefore, information that can be recorded per bit period is one bit.
For read signals on the other hand, the minimum inverting interval of magnetization becomes shorter with an increase in density and, where the adjacent magnetization is inverted (
194
), the read signal is much weakened by interference (
195
). Moreover, the higher the density, the greater the impacts of medium noise and thermal demagnetization, giving rise to a problem that magnetization is lost and errors increase.
Signal processing techniques applicable to such a magnetic disk apparatus include improved versions of the PRML system, such as the extended PRML (EPRML) system and the expanded EPRML (EEPRML) system. These system effectively utilize the energy of signals, weakened by interference, by expanding the energy per bit over the time of delay during which the interference occurs.
Other techniques for expressing signals at multiple levels and recording/reproducing them include a multi-level modulation recording system using an orthogonal modulation technique. There is a system by which information is divided into in-phase and quadrature components and modulated, and combining the so-modulated components makes possible recording of multiple levels. This technique is disclosed in the Japanese Patent Laid-open No. 6-325493. According to this patent application, write information is divided into two signal sequences, of which one is not encoded and the other is convolutionally encoded. Each signal sequence is entered into a circuit known as a signal mapper, and the signals are arranged at quadrature points so arranged on a circle as to maximize the distances between the signals. After the arrangement of signal points, a carrier frequency referencing a system clock is modulated with sine components and cosine components. According to this technique, the resultant modulated waveforms are quantized at a plurality of levels, and signal waveforms having undergone digital-to-analog (D/A) conversion are recorded.
On the other hand, as one of multi-phase quadrature angular modulation systems, there is the continuous phase modulation (CPM) system disclosed in a book by J. G. Proakis and elsewhere.
By the CPM system, information is expressed in phase difference and frequency difference. The modulation waveform of this CPM system, unlike those of usual modulation systems, becomes continuous in symbol periods, has no steep variations. Accordingly, it allows narrowing of the frequency band of the modulation waveform. Therefore, it is known as a modulation system for communication apparatuses including those for wireless communication with a view to enhancing the efficiency of frequency utilization. The prior art in this category includes techniques for enhancing the efficiency of frequency utilization or use for modulation in communications as discussed in J. G. Proakis,
Digital Communications,
3rd edition, pp.190-301, 1995 (first published in 1989). More recently, a combination of differential detecting and Viterbi decoding is disclosed in the Japanese Patent Laid-open No. 9-289529 and elsewhere regarding a technique for use in communication apparatuses as a CPM demodulating method in satellite communication and other situations where sufficient accuracy is not ensured.
Modulation and demodulation in a communications apparatus use a carrier wave. A communications apparatus may use as its carrier either the cosine wave (cos(2&pgr;f
c
t) where f
c
is the carrier frequency and t, the time) of t
Izumita Morishi
Maeda Hideaki
Mita Seiichi
Takashi Terumi
Hudspeth David
Rodriguez Glenda P.
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