DESIGN OF DOHERTY POWER AMPLIFIER

Abstract

The power amplifier is considered to be the ultimate active device in front of an antenna in a transmitter. Since the amplitude of signals is very large, the power amplifier is considered to be a crucial component of the transceiver and thus affects the performance of the entire system. Good efficiency and linearity are the most critical attributes of a power amplifier used in modern applications like IS-95, CDMA-2000 and WCDMA. Both these have always been clashing conditions requiring innovative power amplifier design techniques. To preserve the high efficiency attained over a wide range of the power amplifier operation is another requirement in these applications which results in designing a power amplifier a daunting task. In the present scenario, a more pragmatic approach to this issue is to design a high efficiency amplifier with a non-linear mode combined with linearity improvement technique. A novel technique which improves the efficiency of a linear power amplifier for a wider range of output power has been investigated in this research. The Doherty technique consists of two amplifiers in parallel combined in such a manner that the combination improves the power added efficiency of the main amplifier at 6dB back off from the maximum output power.