Nonlinearity analysis of resistor string A/D converters

A mismatch in the resistor ratio causes nonlinearity in successive-approximation A/D converters fabricated with a
2^{n}R
potentiometric technique. This paper describes a theoretical analysis of this kind of nonlinearity and a method of evaluating the variations in resistance obtained in experiments with monolithic resistors. The resistance variations are classified into a statistically random variation component and a deterministic variation component. The relationship of both components to the nonlinearity error is then clarified. A 7-bit diffused resistor string was fabricated with a silicon-gate NMOS process. An autocorrelation technique was used to identify and separate several resistance variation components in the string. On the basis of the theoretical and experimental results that were obtained, we have developed 10-bit A/D converters and confirmed their accuracy.