The Design of a High-Efficiency Mode-Switching Power Amplifier With a Parallel Combining Transformer for LTE Application

A 2.535 GHz mode-switching power amplifier (MSPA) for LTE (Long Term Evolution) application is presented in 65 nm CMOS process. By using self-biased technology and charge-acceleration-technique in the cascode structure, power-added efficiency (PAE) is increased. A center-tapped parallel combining transformer (PCT) is designed for power combining, which also provides a path for the second-order harmonic shorted ground. The passive efficiency of the transformer maintains above 80% from 2 GHz-3.5 GHz. The output 1-dB compressed power (P
_1dB
) and saturated output power (P
_SAT
) are 23.69 dBm and 28 dBm. The peak PAE of the PA achieved 54.6%. With supply modulator (SM) is employed to improve PAE when the power is back off, the PA delivers 23.4 dBm LTE20 signal with 36.5% PAE.