High-power digital envelope modulator for a polar transmitter in 65nm CMOS

In this paper, an 8-bit envelope modulator as part of a digital polar transmitter for Bluetooth and WLAN is demonstrated. The modulator performs digital-to-analog conversion, up-mixing and power amplification, allowing for an area-efficient, fully-integrated transmitter architecture. The circuit delivers 24.8 dBm peak-power and 16.7 dBm WLAN OFDM power with a mean EVM of 2.7% at 2 GHz. The measured peak-power drain efficiency is 51% while the efficiency for OFDM is 24%. In Bluetooth EDR mode a 19.7 dBm signal with 5%-rms, 13%-peak EVM, and 26% drain efficiency has been measured. The circuit is fabricated in CMOS 65 nm with 50 Aring thick-oxide devices and 2.5 V power supply.