Effects of filtering on the linearity of current-steering IF DAC

Abstract

The distortion of a current-steering digital-to-analog converter (DAC) is often dominated by the signal-dependent output impedance. This has normally been analysed by assuming a purely resistive load. When a digital IF signal is generated, the different harmonic bands are separated and can also be filtered separately. This paper illustrates that linearity can be improved considerably by shorting the generated 2nd harmonic and low-frequency voltage immediately at the DAC's output, so that these can not mix further to any higher order products.