Highly Efficient 5.15- to 5.85-GHz Neutralized HBT Power Amplifier for LTE Applications

A highly efficient fully integrated 5.15- to 5.85-GHz GaAs HBT differential power amplifier (PA) is implemented for long-term evolution (LTE) handset applications considering LTE licensed-assisted access. A simple and practical output network, based on an on-chip transformer, is proposed to achieve low loss. A neutralization technique to mitigate the parasitic base-collector capacitance is also adopted to improve PA performances. The implemented PA achieved a high gain of 26.6-28.1 dB and saturated power of 30.5-31.1 dBm with a high peak power-added efficiency of 40.4%-44.5% under a continuous-wave signal test across 5.15-5.85 GHz. When tested with 20- and 40-MHz bandwidth quadrature phase-shift keying LTE signals, the PA showed an adjacent channel leakage ratio of -33 dBc up to output powers of 24.1-24.4 and 22.2-22.8 dBm, respectively.