Mismatch noise shaper for DAC-SUBDAC structures

摘要

Digital to Analog convertors (DAC's) are prone to mismatch noise, particularly in DAC structures using unequally weighted segments. A digital to analog converter, for use in a data conversion system, for converting a digital input to analog output and having features for reducing mismatch noise comprises a plurality of selectable segments, at least two of which have a first weighting factor and at least two of which have a second weighting factor. The segments when selected are connected to a reference signal, with the output for each segment, when selected, being proportional to the weighting factor of the segments. Selection means select segments based on the digital input. Summing means add the output from each selected segment to produce an analog output. The number of segments having the second weighting factor is equal to at least twice the ratio of the first and second weighting factors less one. Monitoring means monitor the number of times segments having the second weighting factor are selected in a given monitoring period and generate a correction signal when this number drops below a specified target selection value. Borrow means, responsive to the correction signal of the monitoring means, reduce the number of segments selected having the first weighting factor and increase the number of segments selected having the second weighting factor.