| 摘要 |
PURPOSE:To vary the characteristic without increasing the number of passive elements, by combining an amplifier, where the amplification factor is changed by a control signal applied from the external, and passive elements to constitute a filter circuit. CONSTITUTION:An amplification factor K of an amplification factor variable control amplifier 3 is changed considerably by a digital signal applied to logical control input terminals (e) and (f) and is adjusted finely by an analog signal applied to an analog control input terminal (g). A BPF consists of this amplifier 3, resistances R1 and R2, and capacitors C1 and C2. This circuit constitutes a differential circuit, and phase-inverted input signals are applied to input terminals (a) and (b), and output signals are outputted to a terminals (c) and (d). The value of the K of the amplifier 3 is changed logically to change the center frequency of the BPF in steps, and it is changed analogically to correct the center frequency. |
