Improving Power Utilization Factor of Broadband Doherty Amplifier by Using Bandpass Auxiliary Transformer

In this paper, a novel Doherty power amplifier (DPA) configuration with an auxiliary transformer is proposed for broadband operation. Theoretical analysis reveals that the proposed design can offer enhanced power utilization factor (PUF) and wideband Doherty behavior. The optimal design of the auxiliary transformer is identified with an aim to provide good impedance matching and minimal group delay. Based on the proposed theory, a 1.6-2.4-GHz 20-W DPA with improved PUF is designed, simulated, and measured. Under continuous wave excitation, measurement results indicate that the proposed DPA can achieve a PUF of 0.9, good Doherty behavior over the entire frequency band with a 6-dB back-off efficiency of 55%-64%, and saturated efficiency of 68%-76%. In addition, by the use of single-carrier WCDMA signal (centered at 2 GHz) with peak-to-average power ratio of 6.6 dB and at an average output power of 37 dBm, an average drain efficiency of 56% is obtained with adjacent channel leakage power ratio of better than -37 dBc.