| 摘要 |
PURPOSE:To obtain a large time constant with a comparatively smaller capacitance by providing an active circuit charging/discharging a capacitor provided as a time constant element by an input voltage source and supplying a discharge/charge current cancelling the charge/discharge current flowing to the capacitor. CONSTITUTION:A current output obtained from a current mirror 11 of a differential amplifier circuit 10 is fed back positively to a capacitor C. In this case, a resistance of a resistor (R2+r) connected in series with an inverting input (-) of the differential amplifier circuit 10 is selected slightly higher than the resistance of the resistor R connected in series with a noninverting input (+) of the differential amplifier circuit 10, then the positive feedback is applied with the gain that does not exceed the unity and is as closer as possible to the unity. The discharge/charge current (I-i) cancelling the charge/discharge current I1 flowing to the capacitor C is supplied from the differential amplifier circuit 10 by a voltage division output (VCC/2) being an input voltage source. Thus, the actual charge/discharge current to the capacitance C is reduced and the similar effect that the capacitance of the capacitor C being the time constant element is expanded apparently is obtained. |
