Continuous-time data converter with digital multi-stage noise shaping subconverter

A method of operating a continuous-time delta-sigma analog-to-digital converter (ADC), the method comprising:

• filtering an analog input signal using a continuous-time loop filter;
• quantizing an output of the continuous-time loop filter using a multi-bit quantizer to form a quantized signal;
• feeding back the quantized signal to an input of the continuous-time loop filter via a 1-bit or 1.5-bit digital delta-sigma modulator;
• subtracting a quantization error of the 1-bit or 1.5-bit digital delta-sigma modulator from the input of the continuous-time loop filter using a multi-bit digital delta-sigma modulator;
• and
• feeding back a digital signal from an output of the multi-bit digital delta-sigma modulator to an input of the 1-bit or 1.5-bit digital delta-sigma modulator via an all digital feedback path.

A circuit comprising:

• a delta-sigma modulator disposed on a monolithic semiconductor substrate, the delta-sigma modulator comprising:
• an analog loop filter having an input coupled to an analog input node,
• a quantizer coupled to an output of the analog loop filter, and
• a sturdy multi-stage noise shaping digital-to-analog converter (DAC) coupled between an output of the quantizer and the input of the analog loop filter, the sturdy multi-stage noise shaping DAC comprising a 1-bit or 1.5-bit digital delta-sigma modulator, a multi-bit digital delta-sigma modulator configured to modulate a quantization error of the 1-bit or 1.5-bit digital delta-sigma modulator, and an all digital feedback path configured to route a digital signal at a digital output of the multi-bit digital delta-sigma modulator to a digital input of the 1-bit or 1.5-bit digital delta-sigma modulator;
• and
• a functional circuit disposed on the monolithic semiconductor substrate and coupled to an output of the delta-sigma modulator.