Mediatek Corporation

Pao-Ping Ma

Tse-Hsiang Hsu

Han-Wen Hsu

Chih-Hsiung Chu

An apparatus and method for automatic power control is disclosed. An optical recording apparatus utilizes a low-speed, peak-hold circuit to obtain and output a maximum of a front photodiode output signal during a predetermined window or plurality of windows of a total duration long enough to allow maximum peak-hold signal to stabilize. After stabilization, the maximum peak-hold signal is sampled and held in a sample and hold circuit. A reset then clears the signal and reinitializes the peak-hold circuit. In accordance with the difference between a reference voltage and the held peak-hold signal, a feedback controller unit outputs the required current level into a driving unit for producing desired recording pulses into a laser diode for recording information pits into an optical disc. A calibration gain may be used when, due to insufficient FPD response speed, the held signal is different than the real optical power output.

Apparatus and method for automatic power control

An automatic power controller includes a photo detector for detecting the output power of the laser light source and generating a detection signal, a comparator for comparing the detection signal with a reference signal and outputting a comparison signal, a signal source for providing the reference signal with different voltages representing different output power levels of the laser light source to be set, and a gain-adjustable amplifier for receiving the comparison signal and generating an output signal. The gain of the gain-adjustable amplifier is adjusted so that the voltage difference between the steady-state voltage of the comparison signal and the voltage of the reference signal is kept substantially unchanged regardless of the output power of the laser light source, the occurrence of charging/discharging the capacitor in the comparator is reduced. Therefore the automatic power controller can rapidly reach its new steady state while changing the laser output power.

Growing community of inventors

Hsin-Chu, Taiwan

Pao-Ping Ma