Patent ID: 7474235

Claim:
An automatic power control system for an optical disc drive to control the power of laser beam, the optical disc drive comprising a laser diode for receiving a control signal to generate a laser beam; and a photodetector for detecting the laser beam to generate an analog input signal; the automatic power control system, comprising: an analog-to-digital converter, converting the analog input signal into digital data; a down sampling circuit, coupled to the analog-to-digital converter, comprising: a down sampler, receiving a predetermined amount of digital data to generate representation data; a counter, coupled to the down sampler, calculating an amount of the digital data, and resetting the down sampler when the amount equals or exceeds the predetermined count; and a controller, coupled to the counter, disabling the counter when the digital data is invalid; a comparator, coupled to the down sampling circuit, comparing the representation data with predetermined target data to generate error data; and a digital-to-analog converter, coupled to the comparator, converting the error data to analog to generate the control signal.