A 5-GHz 20-dBm Power Amplifier With Digitally Assisted AM-PM Correction in a 90-nm CMOS Process

This paper presents an integrated CMOS power amplifier and a technique for correcting AM-PM distortion in power amplifiers. The linearization technique uses a varactor as part of a tuned circuit to introduce a phase shift that counteracts the AM-PM distortion of the power amplifier. The varactor is controlled by the amplitude of the IQ baseband data in a feedforward fashion. The technique has been demonstrated in a 5-GHz class-AB CMOS power amplifier designed for WLAN applications and implemented in a 90-nm CMOS process. The power amplifier delivers 16 dBm of average power while transmitting at 54 Mb/s (64 QAM). The proposed linearization technique is shown to improve the efficiency of the power amplifier by a factor of 2.8.