The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jun. 07, 1988
Filed:
Dec. 22, 1986
Walter Hirt, Birmensdorf, CH;
Wolfgang Hans Schott, Ruschlikon, CH;
International Business Machines Corporation, Armonk, NY (US);
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).