Patent ID: 7492797

Claim:
A laser driver circuit for driving a laser diode to generate an optical output corresponding to an input data signal with a data transmission rate, the laser driver circuit controlling the optical output based on an output current from a photodiode for detecting the optical output, the laser driver circuit comprising: a biasing section for supplying a bias current to the laser diode; a modulator for generating a modulation current corresponding to the input data signal to add the modulation current to the bias current; a first current-voltage converter for converting the output current from the photodiode into a voltage signal; a first low-pass filter for filtering the voltage signal, the first low-pass filter having a cutoff frequency lower than the data transmission rate; a first amplitude detector for detecting an amplitude of the voltage signal filtered by the first low-pass filter; a reference signal generator for generating a reference signal by receiving the input data signal directly; a second amplitude detector for detecting an amplitude of the reference signal, a second low-pass filter having a frequency characteristic substantially identical with a frequency characteristic of the first low-pass filter, the second low-pass filter filtering the reference signal to output a filtered reference signal to the second amplitude detector, and a filter controller for adjusting the frequency characteristics of the first and the second low-pass filters according to the data transmission rate of the input data signal, the modulator regulating an amplitude of the modulation current according to a difference between the amplitude detected by the first amplitude detector and the second amplitude detected by the second amplitude detector.