Temperature drift stabilized filter circuit

摘要

The output of a filter circuit utilizing a capacitance amplifier circuit is sufficiently stabilized in its temperature characteristics to improve the operational reliability of the circuit. There is provided a DC cutoff filter circuit utilizing a CR circuit constituted by a composite capacitance formed by a capacitance amplifier circuit utilizing an operational amplifier and a series resistor which is grounded to a reference voltage. The reference voltage is a divided voltage output by a voltage follower constituted by an operational amplifier and serves as a virtual ground. Resistors having different temperature coefficients are used. In response to a positive or negative change in the temperature coefficient of the composite capacitance, the reference potential selects the temperature coefficient of the resistors so that the temperature characteristics including those of the amplifier will provide a temperature coefficient which is the reverse of that of the capacitance amplifier circuit, thereby compensating for fluctuation associated with the temperature coefficient of the composite capacitance.