Abstract: A filter circuit using junction capacitors of semiconductors of the present invention prevents the distortion of signal waveforms and is not affected by parasitic capacitors. The filter circuit includes a resistor whose first terminal is connected to an input terminal and whose second terminal is connected to an output terminal. A first junction capacitor is connected between a control voltage supply terminal and an output terminal and a second junction capacitor is connected between the output terminal and ground. An alternate embodiment of the filter circuit includes a pnp transistor, whose emitter is connected to the direct current power supply via a resistor, whose collector is grounded, and whose base is connected to the output terminal.

Abstract: A level shift circuit is provided which maintains DC level of output signals constant by controlling the level variation of the output signals according to DC level variation of the input signal. An input signal is applied to a first circuit comprised of a first buffer, a first resistor and a first constant current source. DC component extracted from the input signal is applied to a second circuit comprised of a second buffer, a second resistor and a second constant current source. A reference voltage and a voltage obtained by subtracting a voltage drop of the second resistor from DC component are applied to an operational amplifier, respectively. An resultant output of the operational amplifier controls the first and the second constant current resources, and then corrects a variation of DC component of the input signal to obtain an output signal having a constant shift level.

Abstract: There is disclosed a filter circuit wherein a current control portion (12) controls a constant current (I.sub.2) specifying the sum of currents flowing in transistors (T119, T120) of a control portion (11) and transistors (T19, T20) of a control portion (9) on the basis of a potential difference between an output voltage (V.sub.1) of an operational amplifier (7) and a constant voltage (V.sub.3) whereby, if there is a difference in voltage level between a control voltage (V.sub.2) of the control portion (9) and the constant voltage (V.sub.3) of the control portion (11), a filter control portion performs the same control as a reference filter output characteristic of a filter portion (8) to an ideal input-output characteristic.