9.6 A 5.3GHz 16b 1.75GS/S wideband RF Mixing-DAC achieving IMD<-82dBc up to 1.9GHz

Abstract

Cellular multicarrier transmitters for communication infrastructure require both high linearity and large bandwidth (BW) at GHz frequencies. The combination of multicarrier GSM, WCDMA and LTE typically requires IMD<;-80dBc and SFDR>80dBc in a large transmit bandwidth of 300MHz and at an output frequency of up to 3.5GHz and beyond. Current-Steering (CS) Nyquist DACs have large BW, but their linearity drops for increasing output frequencies [1]. A separate mixer is therefore needed to generate an RF signal with high linearity. A Mixing-DAC integrates the function of the mixer and DAC together. Using a Mixing-DAC can result in different architecture trade-offs which potentially enable a reduction of the cost and power consumption, while improving the linearity at high frequencies. The state-of-the-art Mixing-DACs attain linearity by means of A2 modulation [2,3] or low sample rate [4], but this results in a limited BW and does not result in a linearity better than IMD=-71dBc. Even a GaAs implementation [5] only achieves IMD=-70dBc while consuming 1.2W.