A linearity improvement technique for overcoming signal-dependent induced switching time mismatch in DAC-Based transmitters

Abstract

This paper presents a linearity improvement technique for overcoming signal-dependent induced switching time mismatch in DAC-based transmitters. By dynamically triggering a dummy final retiming stage, the signal-dependent induced pattern for the switching time of the DAC current source cells is broken. The immediate effect is the significant distortion reduction (IM3 improves up to 15 dB), especially for narrowband signals. Thus, the full linearity potential of these transmitters is achieved by an IM3 of -73 dBc at 1 GHz for only 2 MHz tone spacing. With minimal design optimizations, the overall DAC power consumption increase due to the dummy triggering is limited to only 10%. Two latest generation (40 nm and 28 nm) high-speed wide-band DAC-based wireline transmitters have been used as test vehicles for verifying this technique.