| 摘要 |
PURPOSE:To obtain an automatic power control circuit high in stability by using a variable attenuator to a setting unit which sets the output electric power at a designated level. CONSTITUTION:An input signal is amplified by a power amplifier 1 and turned into an output signal. This output signal is partly extracted by a directional coupler 2 and attenuated by a variable attenuator 7 to which the attenuation degree is set in response to an external level setting signal. Then this attenuated signal undergoes the wave detection through a wave detector 4 and is compared with a reference voltage level by a comparison amplifier. Based on the result of said comparison, the voltage of a power supply for power amplifier is controlled. The power gain of the amplifier 1 is controlled according to the voltage level of said power supply. Thus the output signal is set at a fixed level designated externally and kept at that level.
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