Gain control circuitry for readback apparatus in a PRML magnetic

Details Gain control circuitry for readback apparatus in a PRML magnetic Gain control circuitry for readback apparatus in a PRML magnetic

1986-12-22

1988-06-07

Canney, Vincent P.

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

360 67, G11B 509, G11B 5102

Patent

active

047500581

ABSTRACT:
In the readback apparatus of magnetic recording system operating in accordance with the partial-response maximum-likelihood (PRML) technique, a variable-gain amplifier (VGA) and a maximum-likelihood sequence detector (ML DET) plus a gain control loop are provided. The detector (19) is designed to operate on input signals (y') having nominal discrete signal amplitudes (a, 0, -a) and it furnishes discrete output signals (y) having such nominal signal amplitudes. The gain control loop is responsive to input (27) and output (29) signals of the detector, and it has charge-pump circuitry (37, 39, 41, 43) for generating a gain control signal (V.sub.c =V.sub.g) for the variable gain amplifier (35). To enable proper operation of the system even in case of short-time signal amplitude drops due to media defects, biasing means (49) are provided such that the gain (g) is adjusted to a value which causes the signal amplitudes at the input (27) of the detector to be weighted multiples (ca, 0, -ca) of the nominal amplitude values (a, 0, -a).

REFERENCES:
patent: 4346411 (1982-08-01), Buhler et al.
patent: 4686586 (1987-08-01), Dutcher
R. W. Wood, "Viterbi Detection of Class IV Partial Response on a Magnetic Recording Channel", IEEE Trans. on Comm., vol. COM-34, No. 5, 1986, pp. 454-461.
F. M. Gardner, "Charge-Pump Phase-Lock Loops", IEEE Trans. on Comm., vol. COM-28, No. 11, 1980, pp. 1849-1858.

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