This paper presents for the first time a GaN-based digital class-E outphasing power amplifier (PA) for 5G applications in the 4 GHz range. The amplifier consists of two digital PA MMICs with a 4:1 size ratio between the final-stage transistor gate-widths. A bond-wire-based load network shapes the typical class-E waveform characteristics and combines the two outputs for outphasing at 4 GHz in order to maximize efficiency, also at power back-off (PBO). Moreover, due to the digital design of the PA MMICs the frequency of operation can be easily changed by adjusting the output network, which is a major advantage compared to reactively matched class-E chips.
At 4 GHz a maximum output power (Pout) of 8.4 W and a power gain of 23 dB has been reached for a final-stage drain supply voltage (Vdd) of 27 V. Peak final-stage drain efficiencies (ηdrain) of 84% and 38% were achieved for a Vdd of 10 V at 0 dB and 11.2 dB PBO, respectively. Due to its flexibility regarding digital input and operation modes (PWM, outphasing, switch off one PA) the proposed PA module is a promising candidate to reduce energy consumption in 5G base stations.