A 2×14bit digital transmitter with memoryless current unit cells and integrated AM/PM calibration

This paper presents a 2×14bit cartesian Direct Digital RF Modulator (DDRM) in 28nm CMOS. Both AM and PM calibration circuits are introduced to relax matching requirements of the DDRM units which results in a compact and efficient implementation. The DDRM features a memoryless current source based unit cell to avoid complex dynamic digital predistortion (DPD) algorithms. All the units can be tuned to less than 0.4LSB from their nominal value. When combined with memoryless DPD, ACLR and C-IM3 better than -60dBc is obtained at ~0dBm output power.