| 摘要 |
PURPOSE:To control outputs of power amplifiers by one gain control circuit even when the number of connection stages varies by switching the control input to one gain control circuit to the output of a final-stage power amplifier or the output of an intermediate-stage power amplifier. CONSTITUTION:Power amplifiers 12 and 15 are cascaded and an output is obtained only by the initial-stage power amplifier by making disconnections at points 13 and 14. When large electric power is necessary on the whole, two-stage constitution is used; and the signal 25 outputted from the final stage 15 is inputted from a terminal 20 to an automatic switch circuit 26 to lead the detection output 24 of the final stage 15 inputted from a terminal 22, and a control circuit 27 controls the output of the initial-stage power amplifier 12. When small electric power is necessary, the final stage 15 is disconnected, so no signal is inputted to the terminal 20 and a detection output 23 is led, so that the control circuit controls the output of the power amplifier 12, i.e. output at a terminal 13 according to the detection output 23.
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