Highly Efficient HBT Power Amplifier Using High-Q Single- and Two-Winding Transformer With IMD3 Cancellation

This paper presents a highly efficient InGaP/GaAs HBT power amplifier (PA) implemented using a proposed high- $Q$ single- and two-winding transformer. A single- and two-winding transformer is designed with a printed circuit board (PCB) to combine the output power with a reduced passive loss. Compared to a typical 1:2 two-winding transformer, an additional unit amplifier is connected at the mid-point of the secondary winding to construct a single-winding transformer without additional windings. An IMD3 cancellation technique using a single- and two-winding transformer is also proposed to obtain a high linear output power with high power-added efficiency (PAE) without additional design circuitry. The IMD3 components of the two input currents in the single- and two-winding transformer are 180° out-of-phase cancelling each other at output. The proposed PA is integrated with an InGaP/GaAs HBT process using a PCB transformer. The experimental results demonstrate that the PA achieves a saturated output power of 33.3 dBm, with a PAE of 61.3% at 0.91 GHz. The proposed PA is also tested with an orthogonal frequency-division multiplexing (OFDM) 64-quadrature amplitude modulation (QAM) signal having a bandwidth of 10 MHz and peak-to-average power ratio (PAPR) of 7.8 dB at 0.91 GHz to evaluate the improvement in linearity. The PA achieves an adjacent channel leakage ratio (ACLR) of −42 dBc up to an output power of 26.0 dBm with a PAE of 26.8% and current consumption of 297 mA.