publication_number US 2004239373 A1 abstract according to the present invention there is provided a semiconductor laser driving circuit including a differential output unit which performs differential amplification by receiving complementary input signals and outputs complementary signals from first and second output terminals having an rc filter with a switch obtained by connecting between the first and second output terminals two ends of a switching element two ends of at least one resistor and two ends of at least one capacitor in series two resistors connected in series between a high potential power supply terminal and the first output terminal a high pass filter or bandpass filter which receives an output from a connecting point between the two resistors and passes a component not lower than a predetermined frequency a detection rectifier which receives a signal passed through the high pass filter or bandpass filter converts the received signal into a dc component or low frequency component and outputs the dc component or low frequency component and a hysteresis comparator which receives an output from the detection rectifier outputs an on signal if the received output exceeds a high potential threshold value and keeps outputting the on signal unless the output from the detection rectifier becomes lower than a low potential threshold value wherein the switching element is turned on and the rc filter with the switch starts operating accordingly when the output on signal from the hysteresis comparator is supplied to the switching element application_number US 77963004 A description embodiments of the present invention will be described below with reference to the accompanying drawings 0044 fig1 shows the arrangement of a semiconductor laser driving circuit.