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:
Jan. 30, 2001
Filed:
Feb. 25, 1998
Dale Brian Chapman, San Jose, CA (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
A baseline correction circuit (BCC) that compensates for the offset present on a PWM signal in an optical readback system when associated transients first appear in the PWM signal, and then compensates for the decay in the PWM signal so that significant baseline variations are minimized. The BCC includes a BCC switch coupled to switch the PWM signal responsive to a control unit and a low pass filter coupled through the BCC switch to receive the PWM signal. The low pass filter includes a capacitor coupled between the PWM signal and a ground reference, which stores the voltage of the baseline variation. A difference amplifier is connected to receive the low pass filtered output and also the PWM signal, and to provide a difference signal responsive to the difference between these two signals. The resultant signal is a high-pass filtered version of the PWM signal originally supplied to the BCC. A control unit monitors and controls disk operations, and supplies a transient event signal indicative of a predetermined upcoming baseline variation in the PWM signal, which turns on the BCC switch. At a predetermined time after the transient event has occurred and the baseline voltage has been stored on the capacitor in the low pass filter, the control unit switches off the BCC switch, and the signal from the low pass filter decays at a rate approximately following the input PWM signal into the BCC. Advantageously, such a baseline correction circuit can minimize the dynamic range requirements necessary to handle baseline variations.