A 25 dBm Outphasing Power Amplifier With Cross-Bridge Combiners

In this paper, we present a 25 dBm Class-D outphasing power amplifier (PA) with cross-bridge combiners. The Class-D PA is designed in a standard 45 nm process while the combiner is implemented on board using lumped elements for flexibilities in testing. Comparing with conventional non-isolated combiners, the elements of the cross-bridge combiner are carefully chosen so that additional resonance network is formed to reduce out-of-phase current, thereby increasing backoff efficiency of the outphasing PA. The Class-D outphasing PA with the proposed combiner is manufactured and measured at both 900 MHz and 2.4 GHz. It achieves 55% peak power-added efficiency (PAE) at 900 MHz and 45% at 2.4 GHz for a single tone input. For a 10 MHz LTE signal with 6 dB PAR, the PAE is 32% at 900 MHz with -39 dBc adjacent channel power ratio (ACPR) and 22% at 2.4 GHz with -33 dBc ACPR. With digital predistortion (DPD), the linearity of the PA at 2.4 GHz is improved further to reach -53 dBc, -50 dBc, -42 dBc ACPR for 10 MHz, 20 MHz, and 2-carrier 20 MHz LTE signals.