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Technical Examples
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 POUT of the power amplifier 2 is controlled by regulation of the supply voltage VS. 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 POUT of the respective amplifier stage 3, 4 and 5 is less than the saturation output power PSAT 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.