Noise-shaping of additive dither in analog-to-digital converters

An apparatus comprising:

• an analog-to-digital converter (ADC) having an analog input and a digital output;
• an adder having an analog input, having a dither input, and having an analog output coupled to the analog input of the ADC;
• and
• a dither generation circuit including:
• a digital dither signal generator having an output;
• a digital high-pass filter having an input coupled to the output of the digital dither signal generator, and having an output;
• a digital-to-analog converter (DAC) having an input coupled to the output of the digital high-pass filter and having an output;
• and
• an analog low-pass filter having an input coupled to the output of the DAC and having an output coupled to the dither input of the adder.

A circuit, comprising:

• an analog-to-digital converter (ADC) having an analog input and a digital output;
• an adder having an analog input, having a dither input, and having an analog output coupled to the analog input of the ADC;
• and
• a dither generation circuit including:
• a first sigma-delta modulator having an output;
• a second sigma-delta modulator having an output;
• and
• a digital-to-analog converter (DAC) having a first input coupled to the output of the first sigma-delta modulator, having a second input coupled to the output of the second sigma-delta modulator, and having an output coupled to the dither input of the adder.