| 摘要 |
PROBLEM TO BE SOLVED: To make constant a base-emitter voltage irrespective of the level of a high frequency signal and to prevent the breakdown of a transistor owing to the secular change by controlling the base bleeder voltage of the transistor according to the level of the high frequency signal. SOLUTION: The control voltage 9 of the output of a differential amplifying part 7 is determined by -(resistance 16/resistance 17)×(detection voltage 18 - reference voltage 8). An AGC amplifier is connected to the front stage of a circuit to obtain the relation between a coupling signal 5 and the control voltage 9 with defining that the reference voltage 8 is 2V. The high frequency signal 2 supplied to the base of the transistor 4 is amplified in A-class operation and outputted from an output terminal 15, and the base-emitter voltage keeps the normal voltage. Even if the AGC amplifier is abnormal, a voltage applied to the bleeder resistance is lowered and the base-emitter voltage keeps the normal voltage, so that a reverse bias phenomenon is avoided.
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