A 1–5GHz Direct-Digital RF Modulator with an Embedded Time-Approximation Filter Achieving -43dB EVM at 1024 QAM

Abstract

This paper presents a 1–5GHz direct-digital RF modulator with an embedded time-approximation filter (TAF) to suppress out-of-band noise floor. The proposed TAF technique approximates a FIR impulse response in time domain via a modulated LO waveform, leading to an equivalent RF bandpass filtering during the frequency up-conversion process. The silicon prototype achieves - 43dB EVM for a 10MHz 1024 QAM signal at 2.4GHz with peak stopband noise rejection of > 50 dB.