MICROWAVE MIXER CIRCUIT AND MULTI-SATELLITE RECEIVING DOWN CONVERTER

PROBLEM TO BE SOLVED: To provide a small and inexpensive microwave mixer circuit by controlling the bias voltage to be supplied to the gate of a frequency converting FET via a simple bias switching circuit consisting of a comparator and a transistor. SOLUTION: The voltage of a high potential corresponding to the DC voltage supplied from an intermediate frequency signal output part 19 is applied to the emitter of a transistor TR 10 from a comparator 18 via a bias terminal 12. Thereby the TR 10 is turned on and an FET 8 receives the supply of the stable bias of the constant voltage/current from the TR 10 and is converted into the intermediate frequency with the satisfactory conversion gain. Then the voltage of a low potential is supplied to the emitter of a TR 11 from a comparator 17 via a bias terminal 13. Thereby, the TR 11 is turned off and an FET 9 undergoes no conversion of frequency since no bias is supplied to the FET 9. As a result, only the intermediate frequency signal that is inputted to a microwave signal input part 1 appears at the input side of an intermediate frequency amplifier 16.