Methods and apparatus for tone reduction in sigma delta modulators

A digital to analog converter for providing an analog feedback signal corresponding to a quantized output signal in a sigma delta modulator, the digital to analog converter comprising:

• a plurality of circuit elements, the individual circuit elements having an associated element value, the digital to analog converter being adapted to provide the analog feedback signal using circuit elements selected according to the quantized output signal, the plurality of circuit elements comprising at least one mismatched circuit element having a mismatched element value differing from a design element value by a mismatch amount, and a plurality of matched circuit elements having element values within a tolerance amount of the design element value, the mismatch amount being greater than the tolerance amount.

A method of fabricating a digital to analog converter for providing an analog feedback signal corresponding to a quantized output signal using a group of circuit elements selected according to the quantized output signal in a sigma delta modulator, the method comprising:

• providing a plurality of matched circuit elements in the group in a semiconductor device, the matched circuit elements having element values within a tolerance amount of a design element value;
• and
• providing at least one mismatched circuit element in the group, the at least one mismatched circuit element having a mismatched element value differing from the design element value by a mismatch amount, the mismatch amount being greater than the tolerance amount.