Doherty power amplifiers with improved load modulation for 100 MHz LTE-advanced application

This paper presents the methods to improve load modulation in Doherty along with two modified GaN Doherty power amplifiers (PAs) with high efficiency and linearity at large back-off power for 100 MHz LTE-advanced application. To improve load modulation, the peaking amplifier is designed to achieve similar output current with that of the carrier amplifier by choosing optimal load impedances in class C mode and higher gate biasing voltage. Moreover, to achieve enhanced efficiency at large back-off power, a modified load modulation network (LMN) is designed. To verify those methods, an enhanced Doherty PA and a Doherty PA exploiting modified LMN are designed and measured, respectively. When driven by 100 MHz LTE-advanced signals, the designed PAs achieve adjacent channel leakage ratio of below -48 dBc after digital pre-distortion at 9 dB back-off output power with efficiency higher than 40%.