Patent ID: 7098716

Claim:
A photo-electric pulse conversion circuit that converts an optical pulse signal to a corresponding electrical pulse signal, comprising: a light-current conversion circuit that converts the optical pulse signal to a corresponding current signal and outputs the current signal; either a high-pass I–V conversion circuit that converts the current signal to a pair of corresponding differential voltage signals and outputs the differential voltage signals through a capacitive coupling capacitor, or a differentiating I–V conversion circuit that converts the current signal to a pair of differential voltage signals with a waveform similar to that of signals which are obtained by differentiation of the current signal; a differential amplification circuit with a DC offset cancellation circuit that amplifies the differential voltage signals as a pair of differential input signals and outputs a pair of differential output signals; and a pulse generation circuit that outputs the electrical pulse signal based on the differential output signals; wherein the differential amplification circuit with the DC offset cancellation circuit comprises: a differential amplification circuit that amplifies the differential input signals inputted to a pair of differential input terminals and outputs the differential output signals from a pair of differential output terminals; and a DC offset cancellation circuit inserted between the differential output terminals and the differential input terminals of the differential amplification circuit, the DC offset cancellation circuit being adapted to cancel a-DC offset voltage between the differential output signals; and the DC offset cancellation circuit comprises: a low-pass filter that performs low-pass filtration on the differential output signals inputted thereto so as to output a filtered signal; a mixing circuit that outputs a pair, of mixed differential input signals, which are generated by mixing the filtered signal into the differential input signals such that a negative feedback-is performed, to the differential input terminals of the differential amplification circuit; and a characteristics changing circuit that changes a cutoff frequency and a slew rate of the low-pass filter.