A 2×13-bit all-digital I/Q RF-DAC in 65-nm CMOS

This paper presents a 2×13-bit I/Q RF-DAC-based all-digital modulator realized in 65 nm CMOS. The proposed quadrature up-converter uses a 25% duty-cycle clock to isolate the in-phase (I) and quadrature-phase (Q) modulating signals before combining. Using a 1.2 V supply and an on-chip power combiner, the modulator provides more than 21 dBm RF output power within a frequency range of 1.36 to 2.51 GHz. The peak RF output power, overall system and drain energy efficiencies of the modulator are 22.3 dBm, 31.5%, and 39.7%, respectively. Applying digital predistortion (DPD), 64 & 256 constellation points are measured with EVM better than -30 dB. The measured noise floor is below -160 dBc/Hz, with an IQ image rejection and LO leakage of -65 and -63 dBc, respectively. Its linearity has been evaluated with WCDMA modulation. Using DPD, the linearity improves by more than 15 dB.