Efficiency Enhancement by Sizing Device Periphery for Supply-Modulated Power Amplifiers

In this paper, we introduce an approach aimed at further optimizing the efficiency of discrete drain supply modulated Gallium Nitride (GaN) PAs through transistor sizing. By employing larger periphery transistors, we obtain equivalent output power at lower drain voltages. This capability facilitates a wider relative swing between the highest and lowest dynamic drain voltages, consequently leading to improved back-off efficiency. To validate this methodology, we design and measure two 10 GHz Monolithic Microwave Integrated Circuit (MMIC) PAs, with one employing a larger periphery transistor. Experimental results demonstrate a 5 percentage point (pp) enhancement in average Power Added Efficiency (PAE) when amplifying a 67.5MHz 64-QAM signal using the larger device. Moreover, the measured average gain exhibits a significant improvement of 4 dB with the larger periphery amplifier, while maintaining an unaffected Error Vector Magnitude (EVM) at 5 %.