PURPOSE: To realize a filter of a video band whose circuit integration has been difficult so far by devising a transistor(TR) circuit so that its gain and its cut-off frequency both depend on a capacitance ratio.

CONSTITUTION: A differential amplifier is formed by two TRs Q1, Q2 whose characteristics are identical to each other in this low pass filter. The emitter of the TRs is connected to a low current load 1 (2) respectively. Emitters of both the TRs are connected through the switch 3a of a switched capacitor 3. Through the constitution above, a gain Ga of the circuit is expressed as Ga=C3/C4 and its cut-off frequency fc is expressed in equation. That is, since both gain and the cut-off frequency are dependent on the capacitance ratio, the circuit is suitable for circuit integration.