A multiphase PWM RF modulator using a VCO-based opamp in 45nm CMOS

A VCO-based RF modulator employing multiphase Pulse Width Modulation (PWM) is presented. The proposed RF modulator encodes the baseband signal into a set of multiphase PWM signals which are generated by a VCO-based opamp. The use of PWM avoids broadband quantization noise which is produced by ΣΔ modulation used in other RFDAC-based modulators. The prototype IC is fabricated in a 45nm CMOS process, consumes 54.3 mW, and has an active area of 0.126 mm
²
. The measured results satisfy the 802.11g WLAN spectral mask, and EVM for 10-MHz, 64 QAM OFDM at 2.4 GHz is -30 dB.