| 摘要 |
PURPOSE:To constitute a filter suitable for circuit integration, by using a variable gain amplifier and a capacitor. CONSTITUTION:When a signal is fed to the base of a transistor (TR)Q1, this signal is amplified differentially by TRs Q1, Q2 in an amplifier 2 and picked up at the emitter of a (TR)Q9 after being amplified differentially by TRs Q6, Q7. A capacitor C1 is in parallel connection between the input and output terminals of the amplifier 2, and according to the Miller's effect by the capacitor C1, a capacitance C viewing the amplifier 2 from a resistor R1 is C=C1A1, if the naked gain of the amplifier 2 is taken as A1. Thus, this circuit operates like an LPF, and the output of the LPF is picked up at terminal T2. Further, the cutoff frequency fC of the output of the LPF is fC=1/2piC1A1R1. Even if the value of the resistor R1 is in variance, the cutoff frequency fC can be compensated by changing the gain A1 of the amplifier 2 toward reverse direction, through the change in the collector current of a (TR)Q3. |
