Sigma-Delta versus Binary Weighted AD/DA conversion, what is the most promising?

Though conversion of analog signals to and from digital data is supposed to be a mature, well defined technology, the application in digital signal processing like digital audio unveiled a number of neglected artifacts. Also the correlation between audibility and type of imperfection in the converted signal is only partly covered. Test signals as used on CD records explore only a small part of the converter characteristic with sufficient detail. Bias-dependent glitches, slew-rate distortion, noise-switching, clock-jitter and parasitic coupling, which can seriously degrade the signal, are mostly ignored. The reproduction of low-level signals requires differential linearity to be much better than usually specified. Low-level distortion is produced at every place in the chain between analog input sig- nal and analog output signal where quantization or conversion errors are introduced. In general this distortion is reduced by adding noise as a dither signal to de-correlate errors. The amplitude of the dither varies from one LSB step to several LSB steps, depending on the error to be de-correlated, at the expense of a considerable loss in dynamic range. Error feed-back by noise-shaping can be used to reduce quantization distortion if oversampling is sufficiently high. Dithering or noise-shaping however can emphasize certain non-linearities generated by the D/A converter, e.g. like level-dependent glitches. Converters that guarantee good low-level reproduction are oversampled noise-shaping coders. These coders obtain linearity by time-averaging in stead of by analog precision. They show level-dependent effects different from those of conventional converters, but can more easily be improved by dithering techniques, especially when higher order filters are used in the feed-back loop of the coder. Single chip solutions for converters and anti-aliasing filters with high dynamic range and low dissipation have been realized.