Systematic analysis of the impact of mixing locality on Mixing-DAC linearity for multicarrier GSM

Abstract

In an RF transmitter, the function of the mixer and the DAC can be combined in a single block: the Mixing-DAC. For the generation of multicarrier GSM signals in a basestation, high dynamic linearity is required, i.e. SFDR>85dBc, at high output signal frequency, i.e. ƒout ˜ 4GHz. This represents a challenge which cannot be addressed efficiently by current available hardware or state-of-the-art published solutions. Mixing locality indicates if the mixing operation is executed locally in each DAC unit cell or globally on the combined DAC output signal. The mixing locality is identified as one of the most important aspects of the Mixing-DAC architecture with respect to linearity. Simulations of a current steering Mixing-DAC show that local mixing with a local output cascode can result in the highest linearity, i.e. IMD3<-88dBc at ƒout=4GHz