Noise shaping in digital-to-analog converters using randomizing encoders

Abstract

Techniques for compensating high-speed digital-to-analog converters (DACs) for static mismatch are described. In ideal circumstances, the current sources of a DAC are identical to each other, leading to a frequency response presenting a relatively flat noise spectrum. In the presence of mismatch, however, the response creates unwanted spurious content, which can negatively affect the DAC's dynamic range. The techniques described herein involve randomized thermometric encoders. First, the direction in which a packet contracts or expands, depending on the value to be encoded, can be randomized. Second, pairs of values in a packet (and/or pairs of values outside the packet) can be swapped with one another in a randomized fashion. Third, the decision of whether to apply randomization or not can itself be randomized. By applying one or more of the randomization techniques described herein, the negative effects of switch timing offset and errors in DC linearity can be mitigated.