HIGH-FREQUENCY VARIABLE GAIN AMPLIFYING DEVICE AND RADIO COMMUNICATION EQUIPMENT

摘要

PROBLEM TO BE SOLVED: To stably obtain a tremble gain control width with a small circuit scale for gain control and a simple structure and to save power consumption in a high-frequency variable gain amplifying device. SOLUTION: A high-frequency variable gain amplifying circuit 100A has transistor amplifying circuits 110, 120 and 130, a switch circuit 105 for controlling the supply/shut-off of a source Vdd, and an FET switch circuit 102Q of gate grounding connection which is inserted in on the way of a bypass 103 between an input terminal Ti and an output terminal To. The source of this FET switch circuit 102Q is DC-connected to the drain of the FET 131 of a final-stage transistor amplifying circuit 130, and when the source Vdd is supplied to each of the transistor amplifying circuits 110 to 130 via the switch 105, the FET switch circuit 102Q is turned 'off', while when the source Vdd is shut off, the FET switch circuit 102Q is turned 'on'.