A Wideband IQ-Mapping Direct-Digital RF Modulator for 5G Transmitters

This article presents a wideband $2 \times 12$ -bit direct-digital RF modulator (DDRM) operating in a 0.5-to-3-GHz band for 5G transmitters. The proposed digital Cartesian modulator features an advanced IQ-mapping technique to boost RF power by 3 dB and suppress the $I/Q$ image. To verify the proposed concept, a 40-nm CMOS prototype is implemented whose RF peak output power at 2 GHz is more than 14 dBm. It achieves an adjacent-channel leakage ratio (ACLR) of −52 dBc and an error vector magnitude (EVM) of −40 dB for a 20-MHz 256-QAM signal at 2.4 GHz. With a 320-MHz 256-QAM signal, the measured ACLR and EVM performances are better than −43 dBc and −32 dB at 2.4 GHz, respectively, without using any digital pre-distortion.