OPTICAL RECEIVING CIRCUIT

摘要

PURPOSE:To improve the distortion and especially the low band distortion of a video signal by setting the value at a level smaller than others for a resistance which is connected to the output end of an amplifier from both ends of a coupling capacitor set between a preamplifier and a photodetecting element via a resistance and has one end connected between a capacitor and an amplifier. CONSTITUTION:For the gate voltage of an FFT12, a DC feedback is carried out by a resistance 19 so as to obtain the best operation conditions and therefore the safety is secured in terms of a circuit. A photodetecting element is connected to the FET12 via a capacitor 16, and the capacitor 16 is put into a feedback loop of a feedback type amplifier 13 to improve the frequency characteristics of a low band. The resistance 19 applies the bias voltage to the gate voltage of the FET12; while a resistance 18 improves the frequency characteristics of the amplifier 13 with the resistance value R1 (resistance 19) and R2 set preferably at R1>R2. Therefore just the application of the gate bias voltage of the FET12 is needed since the DC input resistance of the gate of the FET12 is very large.