To obtain a tuning function and a reception band function by simple circuit constitution by providing two functions which use a varactor diode as a variable capacity element and as an ordinary diode respectively.
The outputs from tuning circuits T1 and T2 are led out as balanced outputs from both ends and supplied to a balanced input mixer circuit. When switches S1 to S4 are as shown in the figure, varactor diodes VD1a and VD1b are biased forward with a source voltage Vcc and the tuning circuit T1 is short-circuited. At this time, one varactor diode VD2a or VD2b is biased reverse with the tuning voltage supplied from a PLL circuit, so it has a capacity value matching the voltage, so that the tuning circuit T2 tunes to a desired frequency. Namely, the reception band determined by the tuning circuit T2 is obtained. When the switches S1 to S4 are placed in the state reverse to that in the figure, the states of the varactor diodes are inverted and the reception state determined by the tuning circuit T1 is obtained.
UMEKI YASUNORI
TORAKAWA MAKOTO
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