Switched capacitor power amplifiers (SCPAs) are a class of digital transmitters which have shown promising results for high linearity with good drain efficiency (DE). Their linearity is limited by AM-PM distortion, caused by a difference in output conductance in switching and nonswitching driver cells. Often, digital predistortion (DPD) is required to transmit higher-order modulation schemes. In this letter, a driver cell implementation as an inverter with drain resistors is proposed which has equal output conductance in both cases, aiming to eliminate AM-PM distortion. An SCPA with these driver cells is implemented in a 22-nm fully depleted silicon-on-insulator (FD-SOI) CMOS process which demonstrates excellent DPD-less linearity with an adjacent channel leakage ratio (ACLR) of -50 dB and an error vector magnitude (EVM) of -45.5 dB for 5-MHz 1024 QAM signals at a DE of 8.8%. A matching network exploiting bondwires as high-Q inductors removes on-chip inductors and significantly reduces chip area.
- CMOS integrated circuits
- power amplifiers
- Nonlinear distortion
- switched capacitor power amplifiers (SCPA)
- digital transmitters