PURPOSE: To obtain an output signal waveform having small distortion of pulse width without receiving the effect of the variation of DC voltage caused by the variation of temperature, etc., by using a high pass filter(HPF) so as to AC-combinine a circuit.

CONSTITUTION: The titled circuit is constituted of the HPF 1 connected to an input, a signal state detection circuit 2 connected in parallel with the HPF 1 and HPF 3 as an impulse signal generation circuit and buffers 4 and 5 are respectively provided on the output sides of the HPFs 1 and 3 in order that two signal paths do not form feedback. An inputted binary burst signal is AC- combined by the HPF 1 and added with the impulse signal generated in the impulse generation circuit 3 from the gate signal obtained from the signal state detection circuit 2 so as to be converted into a trinary level signal corresponding to the binary level signal. Thus, the circuit does not essentially receive the effect of the variation of temperature of the signal level and the variation of DC voltage caused by the variation of power source voltages, etc., because it is constituted as the circuit of the AC-combination type.