PURPOSE: To enable DC regeneration without being subject to the effect of noise, by low pass filtering which rejects noise in the signal for a given clamp region only.

CONSTITUTION: In the clamp circuit used for DC regeneration of signal in AC transmission, the buffer amplifiers A1, A2 and A3 have higher input impedance, the output impedance is lower, and especially the amplifier A3 can make DC transmission. Further, the signal A is inputted to the amplifier A1 and LPF consisting of the resistor R1 and capacitor C1, the switch S1 is closed with the control signal B for a given period T1 to output the signal C. This signal C enters the amplifier A2 and is clamped D for a given period T2 with the switch S2 at the clamp section CLP. Further, the output signal E obtained from the amplifier A3 allows to reject the effect of noise for DC regeneration.