| 摘要 |
An active filter circuit has been proposed which is fabricated on a chip and which comprises a two-input operational amplifier with one input for feedback, and a first capacitance element connected between the other input of the operational amplifier and the ground potential. It further comprises a main resistor and the supplemental resistors interconnected in series or parallel, and switches corresponding to the supplemental resistors and turned on or off by control signals, thereby the summed resistance of these supplemental resistors is adjustable to set the time constant created in combination with the capacitance of the first capacitor to a specified value. Input signals are routed to the other input of the operational amplifier via the resistor circuit consisting of the main and supplemental resistors and the switches. According to the present invention, the time constant is detected with a probe pulse by measuring discharge time of the second capacitor. According to the detection results, the control signals are outputted to correct the deviation of the time constant from the specified value.
|
