Filter circuit for integrated circuit

摘要

Transistors Q11 and Q12 constitute a first differential amplifier, their emitters are connected with each other by a resistor R1 and also connected respectively to constant-current sources CS11 and CS12. Transistors Q15 to Q17 constitute a second differential amplifier, and the collector of the transistor Q16 is connected with a current mirror 17. This current mirror circuit 17 is constituted by transistors Q18 and Q19 and resistors R3 and R4. The capacitor 22 is supplied with a current from the current mirror circuit 17, and its voltage is fed back through a buffer circuit 14 to the base of the transistor Q12 as a component of the first differential amplifier.