Gain and Power Enhancement With Coupled Technique for a Distributed Power Amplifier in 0.25- μm GaN HEMT Technology

In this article, a fully integrated 1.0–11.0-GHz wideband distributed power amplifier (DPA) monolithic microwave integrated circuit (MMIC) design is presented. Particularly, a coupled technique with bandpass (CTB) characteristic between the kth output node and the ( $k+1$ )th input node of amplification units (AUs) is adopted in the DPA design. It generates an additional signal reuse path (SRP) to reuse part of the output signal to superimpose the input signal, and then they will be reamplified to the output artificial transmission line (O-ATML). Moreover, due to the bandpass characteristic, the signal reuse can be manipulated to target the upper cutting edges of the working band to alleviate sharp gain and power roll-off. By carefully controlling the SRP, the overall gain, output power, and bandwidth are enhanced and extended. The systematic design approach for the DPA is detailed with circuit implementations and optimizations. To validate the proposed concept, a DPA MMIC prototype is implemented and fabricated in a commercial 0.25- $\mu $ m gallium nitride (GaN)-on-silicon carbide (SiC) high-electron-mobility transistor (HEMT) process. It shows the compact layout within a die size of 3.36 mm2. Under 28-V VDD power supply, the measured results show a flat $14.8\pm 1.0$ -dB small-signal gain with 10.0-GHz wide operating bandwidth and good impedance matching conditions. A saturated output power ( ${P} _{\text {sat}}$ ) of 7.25 W with peak power-added efficiency (PAE) exceeding 38.7% is achieved. The proposed DPA obtains around 1.54–2.16-W/mm2 power density associated with an average PAE of 34.5% over the entire frequency range.