A linear 28nm CMOS digital transmitter with 2×12bit up to LO baseband sampling and −58dBc C-IM3

This paper presents a 1.2-2.6GHz 2×12 bit Direct Digital RF Modulator (DDRM) realized in 28nm CMOS. The digital cartesian transmitter features baseband sampling speeds up to LO. The intrinsically linear architecture features current-mode operation at 25% duty cycle, which requires less predistortion than existing digital transmitters. The applied digital intensive LO modulation reduces the power consumption of the LO distribution. Except for the output stage at 1.8V, the modulator is powered from 0.9V supply. The DDRM features an OP1dB of 15.5dBm. At 3.9dBm output power, the un-calibrated C-IM3 is better than -42dBc, while the image is below -49dBc. With a simple 1D calibration the C-IM3 can easily be improved to below -58dBc. The modulator's peak drain efficiency at 17.5dBm is 34%.