Appeal No. 97-3453 Page 3
Application No. 08/475,374
BACKGROUND
The invention at issue in this appeal relates to digital
magnetic recording. It is an apparatus for recording (i.e.,
writing) data on and reproducing (i.e., reading) data from a
magnetic disk. More specifically, the apparatus includes a
distortion detector and a bias control circuit. The
distortion detector measures a second harmonic distortion
(SHD) of a reproduced signal. The bias control circuit
controls the bias current in the reproducing head to maintain
the SHD at or below -25 dB. By maintaining the SHD at or
below this level, the apparatus minimizes the bit error rate
of data it reproduces.
Claim 2, which is representative for our purposes,
follows:
2. A digital magnetic reproducing apparatus
comprising a reproducing head to reproduce data from
a magnetic recording medium; an equalizer for
shaping, by a partial response method, a waveform of
a reproduced signal output from said reproducing
head; and a decoder for decoding, by a maximum
likelihood decoding method, an equalized reproduced
signal obtained from said equalizer;
said apparatus further comprising:
a distortion detector for measuring a second
harmonic distortion of the reproduced signal; and a
bias current control circuit for controlling a bias
current, which flows in said reproducing head, to
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