Patent ID: 7907500
Filing Date: 2011-03-15
Classification: G11B

Abstract:
1. A radio frequency zero crossing signal generator of an optical disc drive, comprising: a controllable low pass filter, receiving a radio frequency ripple of the optical disc drive, and averaging the magnitude of the radio frequency ripple to generate an average level; a comparator, coupling to the controllable low pass filter, and comparing the radio frequency ripple with the average level generated by the controllable low pass filter to generate a radio frequency zero crossing signal; and a control circuit, coupling to the controllable low pass filter, and adjusting a cut-off frequency of the controllable low pass filter when the optical disc drive reads a fingerprint defect on an optical disc, wherein the speed at which the controllable low pass filter generates the average level is dependent on the cut-off frequency of the controllable low pass filter, wherein the controllable low pass filter comprises a capacitor, a first resistor, a first switch, a plurality of second resistors, a plurality of second switches corresponding to the second resistors, and a third switch, wherein the resistance of the first resistor is different from any of the second resistors, the controllable low pass filter has an input terminal coupling to a first terminal of the first resistor via the first switch, a second terminal of the first resistor is coupled to the capacitor at an output terminal of the controllable low pass filter, the input terminal of the controllable low pass filter is further coupled to first terminals of the second resistors via the third switch, the second terminals of the second resistors are coupled to the capacitor via the corresponding second switches, and the control circuit adjusts the cut-off frequency of the controllable low pass filter by controlling the first, second, and third switches.