Modulation encoders and decoders

Details Modulation encoders and decoders Modulation encoders and decoders

1999-01-04

2001-05-22

Williams, Howard L. (Department: 2819)

Coded data generation or conversion

Digital code to digital code converters

To or from minimum d.c. level codes

C341S083000

Reexamination Certificate

active

06236340

ABSTRACT:

BACKGROUND
This invention relates to modulation encoders for magnetic storage devices.
Modulation codes are often used in magnetic storage devices to insure that a long string of “0's” is not present in a data stream stored on the magnetic storage device. For example, in a tape drive system the presence of a long string of zeros exceeding a constraint value k can cause a circuit with a phase lock loop device that reads/writes data to/from the storage device to lose lock and produce catastrophic data errors.
Different types of magnetic storage systems prioritize code properties such as, timing updates and error propagation characteristics, differently. For tape systems having a small k constraint value (frequent timing updates) is more important than in disk drives, since tape systems require a larger tolerance to velocity changes. On the other hand, if the tape uses an error control scheme such as error detection along a track, as current digital linear tape (DLT) systems do, then minimizing error propagation will have a lower priority.
One type of modulation coding technique uses a table look up to produce code words in response to user data.
One type of modulation code is the so called “block code” technique. In a block code data are operated on a block basis and for m number of bits into an encoder, n number of bits come out. The code rate for such a code is given as m
. In one type of block code, a redundant “pivot” bit is added in the encoded codeword. This pivot bit flags whether there was any need for encoding. If the pivot bit is “1” for example this could signify that the data was not encoded, whereas a “0” would indicate that it was encoded because a k constraint violation had occurred. Usually, such codes are simple to implement but start getting inefficient at higher code rates. A second block code is to use an available block code with a code rate of (n−1)
code for small n and insert interleaved p non-coded bits, resulting in an (n+p−1)/(n+p) code. Such codes are high code-rate, simple to construct and usually have good error propagation properties, but result in large k values. They may be suitable for disk drive applications but are not generally suitable for tape systems.
SUMMARY
According to an aspect of the invention, a modulation encoder includes a base conversion circuit that converts a partitioned input data stream from a first base representation in accordance with the size of groups of bits in the partitioned stream into a second base representation. The base conversion circuit includes a circuit to produce intermediate values of the partitioned stream in the second base representation and a residual value logic circuit that performs modulo-arithmetic on intermediate values modulo the second base representation, and a one's complement logic network fed by the residual value logic to produce output code words.
According to an additional aspect of the invention, a modulation decoder includes a one's complement logic circuit fed by modulation code words to produces residual value words; and a base conversion circuit that converts residual value words from a first base representation into a second base representation to provide original user data.
One or more of the following advantages are provided by the above encoder and/or decoder. The above provides an encoder and/or decoder that has a very high code rate, with a low value of k constraint, that is relatively easy to implement. In addition the maximum error propagation (if the error event is 4 bits or less) is limited to eight bytes for 32/33 codes, ten bytes for 40/41 codes, and six bytes for 24/25 codes. This is accomplished without significantly reducing code rate, relaxing the k constraint or using prohibitively complex implementations.


REFERENCES:
patent: 5144304 (1992-09-01), McMahon
patent: 5347276 (1994-09-01), Gilardi
patent: 5640285 (1997-06-01), Maurice et al.
patent: 6018304 (2000-01-01), Bessios

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