University College Cork

National University of Ireland, Cork

Aidan Keady

Colin Gerard Lyden

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.

Mismatch noise shaper for DAC-SUBDAC structures

Mismatch errors within oversampled analog to digital (ADC) and digital to analog (DAC) data converters limit the overall conversion accuracy. A circuit is provided which interchanges the analog segments within a multibit oversampled converter in a fashion to move the mismatch errors away from the overall converter's passband frequencies and towards other frequencies where they do not interfere with the signal to be converted. The circuit works by minimizing the differences in the signals which control the individual segments. Circuits may be provided for achieving first, second and higher order 'shaping' of the mismatch errors. The invention also provides a circuit in which exchange of the analog elements with the DACs of multibit oversampled converters is effected using a circular queue, so moving the mismatch errors to high frequency where they do not interfere with the signal to be converted.

Growing community of inventors

Moycullen, Ireland

Aidan Keady