Digitally-Controlled Polar Transmitter Using a Watt-Class Current-Mode Class-D CMOS Power Ampli fier and Guanella Reverse Balun for Handset Applications Toshifumi Nakatani, Student Member , IEEE,J e r e m y R o d e, Member , IEEE, Donald F. Kimball , Member , IEEE

Abstract

A digitally-controlled pola rt r a n s m i t t e rw i t ha watt-class CMOS power ampli fier is demonstrated, implemented in a 0.15 m RF CMOS process. Stacked FETs in a current-mode class-D con figuration are used to obt ain high breakdown voltage a n dh i g he fficiency in the output stage, and a doughnut-shaped Guanella reverse balun is applie d to achieve a 1-to-4 impedance transformation with less than 1 dB insertion loss. The ampli fier has 31 dBm output power with 51% drain ef ficiency at 0.75 GHz frequency under single tone testing. The output stage is fed by a buck converter employing d igital pulsewidth modulation with 47 MHz pulse rate synchronized with a 3 GHz clock. Digital compensation techniques were de veloped to maintain linearity. WCDMA HPSK modulation was demonstrated using a pulse pattern generator-based measurement bench. Overall ef ficiency of 26.5% was achieved while maintaining ACLRs within 3GPP specifications at 24 dB m average output power.