PURPOSE: To reduce the number of terminals for connecting external parts and reduce the noise included in an output signal, by incorporating a part of a capacitor on a monolithic semiconductor.

CONSTITUTION: An audio IF signal inputted from an input terminal 1 of a monolithic semiconductor 29 has the amplitude limited by an amplifier 2 and is inputted to the base of a transistor TR 21 through a capacitor 31. The output of the amplifier 2 is outputted to a terminal 3 and has the phase changed by a reactance circuit 9 and is applied to the base of a TR 11 through a terminal 5. The phase difference between signals applied to bases and TRs 21 and 11 is 90° when the signal has the center frequency, and the phase lags to make the frequency lower when the frequency is higher; and therefore, outputs proportional to the phase difference are outputted to terminals 27 and 28. By this constitution, the number of terminals for connecting external parts is reduced. Since low frequency components of the noise generated by the amplifier 2 are suppressed, the noise included in the output signal is reduced.