| 摘要 |
<p>An active filter circuit includes a first (10) and second (14) differential pairs each having a pair of transistors. A capacitor (C1, C2) is connected to a collector of each on transistor of the first and second differential pairs. A first and second negative feed-back paths are connected, respectively, between the collector and a base of one transistor of the first differential pair and between the collector of one transistor of the second differential pair and a base of the other transistor of the first differential pair. By applying suitable voltages to respective inputs of the differential pairs, the active filter circuit functions as a band-pass filter, lowpass filter, high-pass filter, band elimination filter or phase-shifting filter with the same circuit configuration. A current mirror circuit (Q13, Q23) correlatively changes current amounts of the first and second differential pairs in response to a control voltage, whereby a filter characteristic can be changed.</p> |
