An analog-to-digital conversion system uses a fast analog-to- digital converter having a resolution less than the system resolution to convert the difference between a previously predicted value and the current analog value. The converted difference is summed with the predicted value to compute the actual value of the analog input signal to a resolution greater than that of the fast analog-to-digital converter. The high resolution digital value thus obtained becomes the predicted value for the next conversion. This predicted value is converted by a digital-to- analog converter having the same accuracy but not the same resolution as the system output to an analog signal which is compared with the input analog signal to obtain a difference signal. This difference signal is sampled and held to provide the input to the fast analog-to-digital converter. The system includes a gain scaling and switching circuit to compensate for errors which would occur when the difference between the true analog input and the prediction exceeds the range of the low resolution, fast analog-to-digital converter.
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