Complementary metal-oxide semiconductor doherty power amplifier based on voltage combining method

A 1.75 GHz Doherty power amplifier (PA) is designed and implemented in a 0.18-μm complementary metal-oxide semiconductor (CMOS) process. This Doherty PA uses a voltage combining transformer to combine the output power and realise the load modulation which is different from conventional current combining Doherty amplifiers. The prototype has a power-added efficiency (PAE) of 31.6% at a maximum output power of 28.6 dBm from 3.4 V supply voltage. The PAE at 6 dB back-off is still high, about 25%. It shows clearly the efficiency enhancement at the power back-off point because of the Doherty operation. This is the first use of voltage combining techniques in CMOS Doherty PA design.