A 1.8–5.4-GHz GaN MMIC Distributed Efficient Power Amplifier With Reactance Compensation and Adaptive Biasing

This article presents an ultra-broadband distributed efficient power amplifier (DEPA) with reactance compensation and adaptive biasing. It is illustrated that the bandwidth of the DEPA can be improved apparently by applying a shunt short-circuited stub at the combining point. The principle of such method is that the back-off impedance variation with frequency can be compensated by the reactance of the shunt stub. Besides, to get over the high gain compression of the conventional DEPA, an adaptive biasing scheme is proposed for the auxiliary PAs. A DEPA is implemented in a 0.25- $\mu \text{m}$ GaN-HEMT process for validation. The shunt stub is realized by a LC tank equivalently for a compact size. The fabricated DEPA achieves a saturated output power of 41.5–43 dBm and an 8-dB back-off drain efficiency (DE) of 38%–46.8% from 1.8 to 5.4 GHz with a chip size of $3.2\times3.2$ mm2. The fractional bandwidth (FBW) is up to 100%. Applying a 100-MHz LTE signal with an 8.5-dB peak-to-average power ratio (PAPR), an average DE of 35%–43% is measured over the entire bandwidth, and adjacent channel power ratio (ACPR) is better than −47 dBc after applying digital predistortion. To the best of our knowledge, the proposed DEPA demonstrates the largest FBW among all reported integrated back-off efficient PAs without using digital techniques or reconfiguration.