| 摘要 |
PROBLEM TO BE SOLVED: To provide a filter circuit that implements a smooth output change and a time constant adjustable within a fixed range even in the case of duty control of the time of energization of a capacitor.SOLUTION: In an embodiment, the filter circuit includes: an operational amplifier OP1 having an inverting input terminal and an output terminal connected together; a resistor R1 connected between a non-inverting input terminal of the operational amplifier OP1 and an input signal terminal IN; a capacitor C1 connected between the non-inverting input terminal of the operational amplifier OP1 and a ground terminal; a switch SW1 and a capacitor C2 connected in series between the non-inverting input terminal of the operational amplifier OP1 and the ground terminal; and a switch SW2 connected between a junction of the switch SW1 and the capacitor C2 and the output terminal of the operational amplifier OP1. The switch SW1 is controlled on/off by a periodic switch control signal &phgr;, and the switch SW2 is controlled on/off by an inverted signal &phgr;n of the switch control signal &phgr;. The switch control signal &phgr; has a variable duty. |
