A 0.03 to 6 GHz GaN MMIC Power Amplifier with Improved OIP3/Pdc using Nonlinear Cancellation

This study presents an ultra-wideband (UWB) and high-power amplifier (HPA) which employs a two-stage single-transistor driven distributed amplifier (SDDA) architecture to improve the linearity. The gate-bias optimization method for cascaded amplifiers is proposed using nonlinear cancellation theory. By optimizing the bias and thereby changing the higher-order transconductance of transistors in the HPA, a third-order intermodulation sweet spot (IM3-S) can be generated and shifted toward the saturation output region, which can improve the linearity with high output power and high efficiency in a UWB frequency. A monolithic microwave integrated circuit (MMIC) UWB-HPA was designed to validate the proposed method utilizing an in-house 0.25-\mum gallium nitride (GaN) process. The SDDA demonstrates an output power exceeding 10 W across 0.03 to 6 GHz and a power-added efficiency (PAE) greater than 41%. The two-tone measurement results indicate that, when the IM3-S is shifted to 0.9 dB output-back-off (OBO) at 2.6 GHz, the IM3 reaches -33.8 dBc with an output power of 39.5 dBm and a PAE of 41%. At 5.6 GHz, after shifting the IM3-S to 2.2 dB OBO, the IM3 reaches -35.6 dBc with an output power of 37.7 dBm and a PAE of 52%. The ratios of output third-order intercept point to DC power (OIP3/Pdc) reach state-of-the-art values of 39 and 128 at 2.6 GHz and 5.6 GHz, respectively. The results of this study will be helpful for high linearity design of GaN UWB-HPAs.