| 摘要 |
PURPOSE:To decrease the effect of the fluctuation of a DC operating point of an input signal and the fluctuation of an input signal level by using two varactor diodes. CONSTITUTION:The input signal from an input signal source 12 is fed to an input terminal of a buffer 19 via a resistor 13 and an output signal is obtained from the buffer 19. The DC control voltage is impressed to a terminal 21a and the result is outputted form an output terminal of an operational amplifier 21 in same posality and outputted from an output terminal of an operational amplifier 22 in inverse polarity. The bipolar control voltages an impressed respectively to the varactor diodes 14, 17 to control the capacitance. Since the capacitance change in the varactor diodes 14, 17 is cancelled together even when the level of the input signal is changed, the frequency characteristic is not susceptive to the effect of the fluctuation of the DC operating point of the input signal and the fluctuation of input signal level. |
