Methods and apparatus for error cancelation in calibrated current sources

A method to convert digital bits into an analog output signal, comprising:

• configuring a plurality of current sources to output substantially identical current levels;
• selecting a first one of the current sources for calibration according to a calibration sequence;
• and
• assigning respective ones of the plurality of current sources to the digital bits in accordance with a bit-to-current source sequence selected to reduce current error in the analog output, the bit-to-current source sequence being synchronized with the calibration sequence.

A digital-to-analog converter to convert digital bits into an analog output signal,

• comprising:
• a plurality of current sources, configured to output substantially identical current levels in response to respective bits of a digital input code, wherein the current levels vary due to leakage current and according to a calibration sequence;
• a calibrator selectively coupled to the plurality of current sources, configured to adjust the current level of one of the current sources according to the calibration sequence;
• a calibration shift register coupled to the calibrator, configured to selectively couple the calibrator to one of the current sources for one or more calibration clock cycles according to the calibration sequence;
• and
• a current source selector, comprising a plurality of bit assignment shift registers coupled to the plurality of current sources, a first one of the bit assignment shift registers configured to:
• select a second one of the current sources that has a current substantially equal to a desired average current;
• configure the second current source to be responsive to a least significant bit of the digital input code based on the calibration sequence;
• and
• remaining respective ones of the bit assignment shift registers configured to:
• select the remaining current sources by pairs to be responsive to respective remaining bits of the digital input code, wherein current sources responsive to the same bit of the digital input code have substantially equal and opposite current differences from the desired average current.