| 摘要 |
PURPOSE:To easily discriminate the degradation of the transmission characteristic due to the occurrence of third inter-modulation distortion of an amplifier in each stage which is caused by degradation or damage of amplifying elements by providing a monitor circuit which monitors the bias voltage or the current of each amplifying element. CONSTITUTION:A monitor circuit 5 monitors not only a DC voltage VP of the detection output of a detector 2 indicating the power level of the output of an amplifier 1E in the last stage of a multistage amplifier 1 but also bias DC voltages or currents VA to VE of respective amplifying elements of amplifiers 1A to 1E in respective stages. Since an alarm of trouble is sent when these values are on the outside of a certain range, the output level of the amplifier in each stage is not considerably reduced at the time of damage of one amplifying element of this amplifier though balanced amplifiers are used as amplifiers in respective stages. Consequently, bias DC voltages or currents VA to VE of respective amplifying elements of amplifiers in respective stages are considerably reduced and the alarm due to degradation or damage of amplifying elements is sent even when the alarm due to the level reduction of the output power is not sent. Thus, the degradation in transmission characteristic of the amplifier in each stage is easily discriminated to improve the maintainability. |
