| 摘要 |
PURPOSE:To vary only a center frequency on single power source driving basis through an external resistance by connecting inphase inputs of respective operational amplifiers of an active filter consisting of one adder and two integrators using the operational amplifiers to a power source through resistances. CONSTITUTION:The adder consisting of an operational amplifier 1 and resistances R4 and R8, the 1st integrator consisting of an operational amplifier 2, a capacitor C1, and a resistance R1, and the 2nd integrator consisting of an operational amplifier 3, a capacitor C2, and a resistace R2 are cascaded; the output of the 1st integrator is connected to the in-phase input of the amplifier 1 through a resistance R6 and the output of the 2nd integrator is connected to the out-of- phase input of the amplifier 1 through a resistance R to constitute the active filter. A voltage divided through resistances Ra and Rb is connected in common to the respective inphase inputs of the amplifiers 1-3 through a resistance Rc. The resistances R1 and R2 are varied simultaneously while their ratio is held constant to vary only the center frequency, holding the gain and Q constant. Further, a resistance R3 is connected in series to the C2 to compensate the excessive phase rotation of a loop, obtaining original transfer characteristics. |
