Doherty amplifier with DSP control to improve performance in CDMA operation

A power amplifier for CDMA applications which consists of a Doherty amplifier and a digital signal processing (DSP) controller is presented. DSP is used to dynamically adjust the gate bias of the auxiliary (peaking) amplifier at the rate of the signal envelope to obtain gain flatness (i.e. AM-AM distortion correction). Furthermore, DSP is used as a digital predistortor to improve the overall linearity by adjusting the phase at baseband (i.e. AM-PM distortion correction). The 840 MHz Doherty amplifier is realized with two commercially available MESFETs in a hybrid circuit, and the DSP is implemented externally with a board controlled by a personal computer. It is shown that by utilizing these DSP techniques, the overall linearity and efficiency characteristics of the Doherty amplifier can be significantly improved.