D/A conversion with linear-coded weights

Abstract

In design of high-speed, high resolution D/A converters, glitches in the output are of major concern. To tradeoff between hardware complexity and glitch performance the current practice is to use a hybrid converter where the most significant bits are thermometer coded and the least significant bits are binary-scaled. As an alternative to this scheme, we propose a new method for D/A conversion based on linear coding of the weights (1, 2, 3,...). The new method improves the glitch performance and reduces the hardware complexity for high resolution converters. An algorithm for converting the digital binary-coded input word into a digital word controlling the linear weights is given. In an example, the linear-coded weights are applied to a current-steering D/A converter. We discuss properties such as layout properties, device matching, and mixed-signal issues.