| 摘要 |
To effect power control of a power amplifier 2 having three amplifier stages 3, 4 and 5 used to amplify input signals modulated in accordance with a variable envelope modulation scheme, there is used a power amplifier 2 having a gain which reduces as the supply voltage to the power amplifier 2 reduces, and the output power P<SUB>OUT </SUB>of the power amplifier 2 is controlled by regulation of the supply voltage V<SUB>S</SUB>. Taking advantage of the reduction in gain of the power amplifier 2 , it is ensured that, in respect of each respective amplifier stage 3, 4 and 5 and at each respective value of the supply voltage in the voltage control range, the output power P<SUB>OUT </SUB>of the respective amplifier stage 3, 4 and 5 is less than the saturation output power P<SUB>SAT </SUB>of the respective amplifier stage 3, 4 and 5 . As a result, distortion of the signal is reduced. The power control technique improves efficiency over known techniques of backing off the output power and using a variable gain amplifier stage to control the output power.
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