SWITCHING POWER amplifiers (PAs) boast higher efficiency compared to linear PAs. Yet they cannot be directly applied in systems employing spectrally efficient modulation. One solution proposed to "break" this tradeoff is polar modulation. At the University of California, a 2.4-GHz mixed-signal, polar-modulated PA in 65-nm CMOS has been demonstrated by Debopriyo Chowdhury, Lu Ye, Elad Alon, and Ali M. Niknejad.
Their digitally modulated polar transmitter houses a 2.4-GHz switching, Inverse Class D PA. When operating from a 1-V supply, that PA delivers +21.8 dBm peak output power with 44% efficiency. The transmitter also integrates the local-oscillator (LO) distribution network and digital drivers. To aid in the removal of spectral images for improved coexistence, this solution relies on low-power digital filtering on the amplitude path.
Thanks to simple static predistortion, the transmitter meets error-vector-magnitude (EVM) and mask requirements of IEEE 802.11g WLAN data with 18% average efficiency at +14 dBm output power. At this performance level, the transmitter consumes an average of 150 mW. See "An Efficient Mixed-Signal 2.4-GHz Polar Power Amplifier in 65-nm CMOS Technology," IEEE Journal Of Solid-State Circuits, Aug. 2011, p. 1796.
