Resolution improvement in an analog‐to‐digital converter by the superposed dither signal

This paper discusses a method to improve the resolution of an analog‐to‐digital (A‐D) converter to detect differences less than 1 LSB (least significant bit) in the input signal. Resolution is improved by superposing dither on the input signal and averaging over many measurements. The theory and experimental verification for this method are described. This analysis calculates numerically the expectation value of the result of A‐D conversion and the expectation value of the variance, with the dither superposed on the input signal. The results show that for larger amplitude of dither, the expectation value of A‐D conversion comes closer to the real value, and the expectation value of the variance becomes larger. The relation between the amplitude of dither and the improvement of resolution is calculated as a function of the number of measurements. For example, when the number of measurements is 100 and the amplitude of dither is 0.4 LSB, the resolution can be improved to 0.05 LSB. This analysis is verified experimentally by using a white noise generator as a dither source, dc voltage standard as a signal source, and a transient recorder as an A‐D converter.