| 摘要 |
PURPOSE:To enable a circuit to vary the gain of a differential amplifier and to obtain the differential amplifier suitable for circuit-integration by controlling a transistor (TR) connected in parallel to a TR constituting the differential amplifier by an external signal to change the collector current of the TR constituting the differential amplifier. CONSTITUTION:Since the sum of the collector current of TRs 5, 6, 13, 14 is limited to a fixed value by a constant current circuit 10, the collector current of the TRs 5, 6 is also changed when the collector current of the TRs 13, 14 is changed by inputting a gain controlling signal from a terminal 7, so that the gain of the differential amplifier can be changed. The TRs 5, 6, TRs 13, 14 and resistors 15, 16 are symmetrically arranged with equal characteristics, so that the changed quantities of the collector current of the TRs 5, 6 are equal to each other. The resistors 15, 16 are inserted in order to prevent the deterioration of characteristics by the inner capacitance of the TRs 13, 14 in the high frequency area of the differential amplifier. |
