RF power amplifiers (PA) are the final amplification stage before the antenna in a base station transmitter. Base station transmitted signals must be spectrally efficient to achieve the highest channel capacity available in the GSM transmit band. Two major characteristics of PAs are linearity throughout the dynamic range and efficiency. Class A tuned PAs easily meet this linearity requirement by offering a low collector/drain efficiency. PAs with a low collector/drain efficiency require a higher DC power supply and more complex cooling system. Therefore, base station PA design is based on a trade-off between linearity and efficiency, and operating these amplifiers in class AB is a reasonable compromise.
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