Patent ID: 7307939

Claim:
An apparatus for controlling write power in an optical driver, comprising: a laser diode which emits light; a monitor photo diode which monitors the amount of the light emitted from the laser diode; a controller which determines whether the write power provided to the laser diode is stable based on a signal generated by sampling and holding a predetermined section of an output of the monitor photo diode, and controls the write power provided to the laser diode by adjusting the number of channels used according to whether the write power provided to the laser diode is stable; an amplifier which amplifies the output of the monitor photo diode; a digital/analog converter having first, second, third and fourth channels, wherein the first, second, third and fourth channels transmit first reference, second reference, overdrive power and a predetermined percentage of an expected write power voltages, respectively; a write channel APC (auto laser diode power control) circuit which provides a write channel voltage based on the signal and the first reference voltage, and provides the signal to the controller; a read channel APC circuit which provides a read channel voltage based on the signal and the second reference voltage; and a laser diode driver which provides the write power corresponding to the write channel, read channel, overdrive power and the predetermined percentage of the expected write power voltages to drive the laser diode, wherein write channel APC circuit comprises: a sampler and holder which samples and holds a predetermined section of a voltage corresponding to the output of the monitor photo diode; an operational amplifier which amplifies the voltage output from the sampler and holder using a reference voltage; and a differential amplifier which compares and determines the difference between the amplified voltage of the operational amplifier with the first reference voltage, wherein the differential amplifier outputs the result of subtracting the difference from the first reference voltage as the write channel voltage in response to the amplified voltage being greater than the first reference voltage, and outputs the result of adding the difference to the first reference voltage as the write channel voltage in response to the amplified voltage being smaller than the first reference voltage.