A new switch compensation technique for inverted R-2R ladder DACs

Many recent applications are based on DSP and interfaced to I/O with data converters. In this context, high-performance DAC have become crucial building blocks. The current-steering-flash DAC architecture is the most popular architecture for its inherent speed potential. Resolution of these converters is limited by component mismatches, thus gradients and random device variations challenge the analog designers. In high resolution DAC, static specifications are reached thanks to trimming, and dynamic performance is mostly determined by current-steering switch performance. On one hand, mandatory presence of switches impacts static performance, and compensation techniques must be used to cancel switch effects on linearity and gain. On the other hand, dynamic performance is strongly dependent on switch design and operation. In this paper, we present a novel switch compensation technique for inverted R-2R ladder DACs. While traditional switch compensation in the ladder leads to very large switch devices, our method allows current-steering with reduced-equally-sized-switches. This new design method preserves static performance and opens the door to improved dynamic performance. Other improvements include reduced area for both the analog and the digital sides of the converter.