Co-Design of Doherty Power Amplifier and Post-Matching Bandpass Filter

This paper presents a novel co-designed Doherty power amplifier (DPA) and a post-matching output bandpass filter. The filter is designed as a matching network to present the desired impedance at the combining node of carrier and peaking paths, thus eliminating the quarter-wave transformer of the conventional Doherty combiner network. This co-design method minimizes the circuit complexity and inter-connection loss, leading to an enhanced overall performance. A prototype is designed and implemented using GaN transistors and third-order Hairpin filter with 20% bandwidth centered at 3.6 GHz. The measured frequency response exhibits desired amplifier-filter function, and Doherty efficiency enhancement are experimentally demonstrated with efficiency of 68% and 55% at saturation and 6-dB back-off regions. Modulated measurement shows excellent linearity (−37-dB adjacent channel leakage ratio) and efficiency (47%) for transmitting the LTE signal with 10.5-dB PAPR.