Dither signal insertion inversely proportional to signal level in delta-sigma modulators

A sigma-delta modulator of a type that includes a quantizer, comprising:

• a rectifier that rectifies an input signal to the quantizer to provide a rectified output signal having an amplitude that is inversely proportion to the amplitude of the input signal of the sigma-delta modulator;
• a first bank of voltage-variable capacitances coupled in parallel to a first input node of said quantizer and a second bank of voltage-variable capacitances coupled in parallel to a second input node of said quantizer;
• and
• a plurality of switches operated pseudorandomly for selectively applying either the rectified output signal or another signal to control terminals of said voltage-variable capacitances, where the magnitude of the rectified output signal controls a value of the total capacitance presented to the input nodes of the quantizer for generating a dither signal having a pseudorandom amplitude that is inversely proportional to the amplitude of the input signal of the sigma-delta modulator.

A sigma-delta modulator of a type that includes a quantizer, comprising:

• at least one window detector that compares an input signal to the sigma-delta modulator to a pair of threshold potentials to generate a window detection signal;
• a first bank of voltage-variable capacitances coupled in parallel to a first input node of said quantizer and a second bank of voltage-variable capacitances coupled in parallel to a second input node of said quantizer;
• a pseudorandom signal generator having an input clock signal that is selectively gated on or off by said window detection signal;
• and
• a plurality of switches coupled to said pseudorandom signal generator and operated pseudorandomly thereby for selectively applying either a first voltage potential or a second voltage potential to control terminals of said voltage-variable capacitances to control a value of the total capacitance presented to the input nodes of the quantizer for generating a dither signal having a pseudorandom amplitude that is inversely proportional to the amplitude of the input signal.