SAW-Less Direct RF Transmitter With Multimode Noise Shaping and Tri-Level Time-Approximation Filter

This article presents a multimode direct radio frequency (RF) transmitter capable of a high in-band dynamic range and a low out-of-band (OOB) noise floor. It features a hybrid digital-to-analog converter (DAC) with a reconfigurable dual-band delta–sigma modulator to lower the quantization noise floor at one or two frequency bands. Additionally, a tri-level time-approximation filter is proposed to further suppress OOB noise with high tunability and stopband attenuation. The objective is to demonstrate a low-noise floor without using a surface acoustic wave (SAW) filter. For a 256-quadratic-amplitude modulation (QAM) signal with 17.4-dBm average output power at a 2.2-GHz carrier, the silicon prototype achieves −40-dB error vector magnitude (EVM) and −169-dBc/Hz noise spectral density (NSD) at 68-MHz offset by consuming a total power of 1.2 W.