| 摘要 |
PURPOSE:To extend the controllable range of transmission power level, by adding a means which changes a signal transmission amount transmitted from a power amplifier to a detector with an electric signal corresponding to a reference voltage value. CONSTITUTION:When a switch 16 is opened, a part of an output of a power amplifier 11 is detected at a detection diode 131 of a detector 13 via a directional coupler 12. A detected voltage is picked up at a load resistor 132 and applied to an inverting terminal of an operational amplifier 141 costituting an inverting amplifier 14. An output voltage of the inverting amplifier is applied to a PIN diode variable attenuator 17 to change the input power to the power amplifier 11. When the switch 16 is closed, the operating point of the operational amplifier 141 is decreased and an output power level is lowered. When the switch 16 is open, a switch 20 is closed and a capacitor 201 is grounded. The amount of coupling of the directional coupler 12 is a value relating to the capacitor 201, and the upper limit value of the power level which can control the output power can be determined by setting the capacitor to a suitable value. |
