A GaAs HBT Doherty Power Amplifier with 31 dBm Linear Output Power and 43% Efficiency by Using Dynamic IM3 Cancellation

This paper presents a comprehensive design of three-stage fully differential linear Doherty power amplifier (DPA) for 5 G new radio (NR) handset applications with low supply voltage of 3.4 V. This proposed DPA is implemented by 2 um GaAs HBT Flip-chip process while output transformer and matching networks are achieved by 6-layer laminate substrate process. Besides the bias currents of each stage, the size and load impedance of the amplifier in the peak path were optimized to cancel the non-linearity components of carrier amplifier dynamically. The broadband transformer and equivalent lowpass network of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda / 4$</tex> transmission line were designed to expand the bandwidth of impedance transform in DPA. This work achieves both linearity and high efficiency within a broadband of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3.3-4.2 \text{GHz}$</tex>. For continuous-wave (CW) signal, the implemented DPA module exhibited a saturation power from 34 to 35.3 dBm, and PAE from 42 to 52 % in full N77 band. Using the 5G new radio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$100-\text{MHz}$</tex> QPSK signal, this work shows high linear power of 31 dBm with 43 % PAE and 30 dBm with 33% PAE at N78 and N77 band, respectively. The corresponding adjacent channel leakage ratios (ACLRs) are lower than −40 dBc without digital pre-distortion (DPD).