Cost reduced interpolated timing recovery in a sampled amplitude read channel
First Claim
1. A sampled amplitude read channel for reading information stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values, the interpolated sample values generated by interpolating a sequence of discrete time channel sample values generated by sampling pulses in an analog read signal from a magnetic read head positioned over the magnetic medium, the sampled amplitude read channel comprising:
- (a) a sampling clock;
(b) a sampling device, responsive to the sampling clock, for sampling the analog read signal to generate the channel sample values;
(c) an interpolated timing recovery circuit, responsive to the channel sample values and an interpolation interval τ
, for generating the interpolated sample values using an interpolation filter having an actual impulse response h(n) comprised of a number of actual coefficients computed in real time as a function of τ and
a matrix of predetermined values Gi (n), wherein;
i equals 1 to L where L determines a degree that the actual coefficients approximate ideal coefficients;
n equals 1 to N where N is the number of actual coefficients in the actual impulse response h(n);
the ideal coefficients are represented by a matrix A;
the function of τ
is a lookup table into a matrix F; and
the matrix F is a factor of a rank reduced approximation of matrix A; and
(d) a discrete time detector for detecting the digital data from the interpolated sample values.
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Abstract
A sampled amplitude read channel reads information stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values, the interpolated sample values generated by interpolating a sequence of discrete time channel sample values generated by sampling pulses in an analog read signal from a magnetic read head positioned over the magnetic medium. A write VFO generates a write clock for writing digital data to the magnetic medium at a predetermined baud rate for a selected zone, and upon read back, the write VFO generates a sampling clock at a frequency slightly higher than the write frequency. A sampling device samples the analog read signal at the sampling clock rate to generate a sequence of discrete time channel samples that are not synchronized to the baud rate, and the channel samples are equalized by a discrete time equalizing filter according to a predetermined partial response (PR4, EPR4, EEPR4, etc.). An interpolating timing recovery circuit, responsive to the equalized channel samples, computes an interpolation interval τ and, in response thereto, generates interpolated sample values substantially synchronized to the baud rate. The timing recovery circuit also generates a data clock for clocking a discrete time sequence detector which detects the digital data from the interpolated sample values. In a cost reduced implementation, the interpolation filter coefficients are computed in real time as a function of the interpolation interval τ.
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Citations
20 Claims
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1. A sampled amplitude read channel for reading information stored on a magnetic medium by detecting digital data from a sequence of discrete time interpolated sample values, the interpolated sample values generated by interpolating a sequence of discrete time channel sample values generated by sampling pulses in an analog read signal from a magnetic read head positioned over the magnetic medium, the sampled amplitude read channel comprising:
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(a) a sampling clock; (b) a sampling device, responsive to the sampling clock, for sampling the analog read signal to generate the channel sample values; (c) an interpolated timing recovery circuit, responsive to the channel sample values and an interpolation interval τ
, for generating the interpolated sample values using an interpolation filter having an actual impulse response h(n) comprised of a number of actual coefficients computed in real time as a function of τ and
a matrix of predetermined values Gi (n), wherein;i equals 1 to L where L determines a degree that the actual coefficients approximate ideal coefficients; n equals 1 to N where N is the number of actual coefficients in the actual impulse response h(n); the ideal coefficients are represented by a matrix A; the function of τ
is a lookup table into a matrix F; andthe matrix F is a factor of a rank reduced approximation of matrix A; and (d) a discrete time detector for detecting the digital data from the interpolated sample values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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18. The sampled amplitude read channel as recited in claim 17, wherein the actual impulse response h(n) is generated by minimizing:
- ##EQU22## C.sub.τ
(ejω
) is the frequency response corresponding to the actual impulse response h(n);ejω
τ
is the frequency response corresponding to the ideal impulse response;α
is a fractional value where 0<
α
≦
1; andX(ejω
) is a frequency response of the read channel.
- ##EQU22## C.sub.τ
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19. The sampled amplitude read channel as recited in claim 18, wherein X(ejω
- ) is selected from the group consisting of PR4, EPR4 and EEPR4.
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20. The sampled amplitude read channel as recited in claim 1, wherein the interpolated timing recovery further comprises:
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(a) a means for computing an interpolation interval τ
proportional to a time difference between a channel sample value and a desired interpolated sample value; and(b) a zero phase start circuit comprising a means for computing an initial interpolation interval τ
.
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Specification