| 摘要 |
PURPOSE:To realize a system which can protect a transistor of output stage with sufficient redundancy for a high-frequency power amplifier which is converted to a transistor, by controlling the output power based on the reflected power given from a load. CONSTITUTION:The high-frequency power to be applied to an input terminal 16 is amplified up to the level set by a manual control variable resistor 14 at a control part 3 by a variable gain amplifier 1 to be supplied to a power amplifying part 2. The power is supplied through the part 2 to power amplifiers 5-7 via a distributor 4. The outputs of these amplifiers are synthesized in terms of electric power by a synthesizer 8 to be supplied to a load 20. The reflected power is detected by a directional coupler 16 of the amplifiers 5-7 and changed into a direct current through a wave detector 17 to be supplied to a maximum value detecting circuit 9. In case the reflected power is small, the detected voltage at the part 2 is isolated from a control circuit 12. The detected voltage is applied to the circuit 12 by a comparator 10 and via a switch circuit 11 to reduce the gain of the amplifier 1 in case the reflected voltage increases and the output voltage of the circuit 9 exceeds the level set by a working level controller 13. |
