A Digital Polar Transmitter With DC–DC Converter Supporting 256-QAM WLAN and 40-MHz LTE-A Carrier Aggregation

Abstract

A digital polar transmitter is introduced using 9-b thermometer-coded uniform cells for wideband signal. By analyzing amplitude and phase paths impairment which causes both in-band and out-of-band distortions, a 960-MHz delay tuner is designed for precise amplitude and phase alignment. Furthermore, two digital pre-distortion algorithms for digital power amplifier (DPA) are implemented and compared. Importantly, an on-chip dc–dc converter is included for direct battery connection and output power control. Boosted cascode gate bias improves PA efficiency at low power region. The proposed design is fabricated using a 55-nm RF CMOS technology. This DPA including digital amplitude modulation (AM) filtering achieves peak power of +21.9 dBm with 41% drain efficiency in continuous-wave measurements. It achieves EVM of 2.9% with 20-MHz IEEE 802.11ac compliance of 256-QAM OFDM signal, and also achieves EVM of 4.5% (CC0)/4.8% (CC1) with 40-MHz LTE-A carrier aggregation compliance of 64-QAM OFDM signal.