Pulse or digital communications – Equalizers
Reexamination Certificate
2000-04-18
2004-09-07
Chin, Stephen (Department: 2634)
Pulse or digital communications
Equalizers
C375S232000
Reexamination Certificate
active
06788739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology of reproducing data which is digitally recorded or digitally transmitted, particularly to a data reproducing system using PRML (Partial Response Maximum Likelihood) for executing partial response equalization suitable for a characteristic of a transmission path.
More in details, the present invention relates to an apparatus and a method of equalizing a waveform for reducing an equalization distortion by equalizing the waveform in a desired frequency characteristic, particularly to an apparatus and a method of equalizing a waveform for executing equalization by using PR1 (Partial Response Class 1) of a low frequency region emphasizing type to thereby realize accurate data detection.
2. Description of the Related Art
In the technical field of information processing, much data is handled after having been digitized. That is, softwares necessary for starting an information processing system or controlling operation thereof or data formed on the system are stored in a magnetic disk type recording apparatus such as a hard disk drive as a digitized file or are transmitted via a network such as LAN (Local Area Network) or the like. On the other hand, in order to reutilize data, analog waveform data read from a magnetic disk or analog waveform data received from a transmission path needs to digitally reproduce accurately.
Originally, in record data or transmission data, binary data comprising 0 and 1 is expressed in a square hit form. For example, in a magnetic disk type recording apparatus, data is reproduced by using a rise pulse and a fall pulse of a square wave by differentiating a signal read from a magnetic head. However, the rise and the fall pulse waves are accompanied by waveform rounding. When a recording density is promoted, an interval between the pulse waves becomes narrow by that amount and the pulse waveforms interfere with each other to thereby make difficult reproduction of data.
For example, due to an increase in the number and size of files handled by an information processing apparatus, the need for a large capacity formation and promotion of a record density with regard to a magnetic disk type recording apparatus such as a hard disk is required. The increase in the record density signifies a reduction in a volume of a magnetic member per bit of data. Accordingly, magnetic force is naturally reduced, a reproduced signal is weakened and noise is magnified relatively. Therefore, in the technical field of digital recording, a technology for accurately reproducing data from a weak reproduced signal becomes indispensable.
Such a problem of digital reproduction naturally exists not only in a digital recording apparatus but also in a digital communication apparatus.
In order to realize further accurate data reproduction, a technology referred to as so-to-speak PRML (Partial Response Maximum Likelihood) has been used widely. This is constituted by combining two data reproducing systems of a partial response system and a Viterbi decoding system. The partial response system provides equalization, that is, operation of neatly arranging a waveform of a reproduced signal. Further, the Viterbi decoding system is provided with maximum likelihood, that is, operation of reproducing data string which is mostly probable in view of the probability.
In an extremely simple expression, equalization of a waveform is realized by isolating respective pulse waves by exalting a high frequency component of a reproduced waveform. However, when the high frequency component is extremely exalted, in accordance therewith, rise at a low frequency is also amplified. Therefore, there has widely been adopted a system of permitting waveform interference partially, which is referred to as partial response.
The partial response is provided with a plurality of classes indicating equalization references of PR4 (Partial Response Class 4) and PR1 (Partial Response Class 1). PR4 is provided with an equalized frequency characteristic of (1−D) (1+D) and is expressed in an equivalent block diagram as shown by FIG.
6
A. Further, PR1 is provided with an equalized frequency characteristic of (1+D) and is expressed in an equivalent block diagram as shown by FIG.
6
B. Incidentally, shown in
FIGS. 6A and 6B
designates an operator expressing delay of 1 channel clock. Therefore, PR4 signifies (1−D) (1+D) =1−D
2
, that is, a difference is calculated from a current component by square of a component forward by 1 clock, further, PR1 signifies to add the component forward by 1 clock to the current component.
It is general to constitute a PR4 equalizer by using a 7 pole 2 null equiripple filter. This is derived from that the equiripple filter is provided with a flat phase characteristic and setting of parameters is comparatively easy. With regard to the PR4 equalizer, for example, there is a description in “A 27 MHz Programmable Bipolar 0.05; Equiripple Linear-Phase Lowpass Filter” by Greet A. De Veirman et al, (1992 IEEE International Solid-State Circuits Conference).
In contrast thereto, PR1 equalization can arrange a waveform by reducing a degree of exalting a frequency component and is suitable for a magnetic disk having a high linear density, that is, high record density. Since PR1 executes a low frequency region emphasizing type equalization, conventionally, a PR1 equalizer is often constituted by combining an integral equalizer with a filter for emphasizing a high frequency region as well as attenuating a component at a vicinity of a Nyquist frequency, a filter for correcting group delay or the like.
However, in the case in which the PR1 equalizer is constituted by a combination of such many filters, it is not easy to flatten a phase at a high frequency region and accordingly, it is difficult to promote the equalization characteristic. Further, although a degree of freedom is enhanced by an amount of increasing parameters, on the other hand, it is very difficult to set optimum parameters.
According an example of a conventional PR1 equalizer, the PR1 equalizer is constituted by a combination of a highpass filter and a 6-th order lowpass filter. In this industry, generally, an amount of calculation for setting parameters of a circuit is expanded exponentially in accordance with an order degree provided to the circuit and it is very difficult to calculate an optimum solution of such an high order PR1 equalizer. Further, a circuit for constituting the equalizer becomes large-scaled in accordance with the order degree and power consumption is increased by that amount.
SUMMARY OF THE INVENTION
In order to realize application of a PR1 equalizer suitable for a high linear density to a data reproducing apparatus, this must be realized by a simple circuit constitution. Further, it seems to be necessary that optimum parameter setting of PR1 equalization is calculated easily in accordance with a simple algorism.
It is an object of the present invention to provide an excellent data reproducing system using PRML (Partial Response Maximum Likelihood) for executing partial response equalization suitable for a characteristic of a transmission path.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for enabling accurate data detection by reducing equalization distortion by equalizing a waveform to a desired frequency characteristic.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for executing equalization by using PR1 (Partial Response Class 1) of a low frequency region emphasizing type.
It is a further object of the present invention to provide an excellent waveform equalizing apparatus and its method for reducing a circuit scale and realizing a PR1 equalizer by reducing power consumption.
The present invention has been carried out in consideration of the above-described problem and a first aspect thereof is a waveform equalizing apparatus for equalizing an in
Chin Stephen
Frommer William S.
Frommer & Lawrence & Haug LLP
Smid Dennis M.
Sony Corporation
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