Direct feedback for continuous-time oversampled converters

An apparatus comprising:

• a continuous-time sigma-delta analog-to-digital converter comprising:
• a first integrator stage;
• a second integrator stage to receive an output from the first integrator stage;
• a third integrator stage to receive an output from the second integrator stage;
• an outer feedback loop comprising a digital-to-analog converter to convert a quantized output signal to an analog signal that is fed back to an input of the first integrator stage;
• and
• an inner feedback loop comprising a current-mode digital-to-analog converter to convert the quantized output signal to an analog current feedback signal that is provided to an output of one of the integrator stages such that the analog current feedback signal and the input of that integrator stage are both integrated by the integrator stage.

An apparatus comprising:

• a continuous-time sigma-delta analog-to-digital converter comprising:
• a first integrator stage;
• a second integrator stage comprising a current amplifier driving an integrating capacitor;
• an outer feedback loop that includes a first digital-to-analog converter to convert a digital output signal to a first analog feedback signal that is provided to the first integrator stage;
• and
• an inner feedback loop that includes a current-mode digital-to-analog converter to convert the quantized output signal to an analog current feedback signal that is provided to an output of the second integrator stage, in which both the current feedback signal and an input signal of the current amplifier in the second integrator stage are integrated by the integrating capacitor in the second integrator stage.

A method comprising:

• converting an analog input signal to a digital output signal using a continuous-time sigma-delta analog-to-digital converter, the analog-to-digital converter comprising a first integrator stage and a second integrator stage, the second integrator stage comprising a current amplifier that drives an integrating capacitor, including
• converting the digital output signal to a first analog feedback signal that is provided to the first integrator stage;
• converting the digital output signal to a second analog feedback signal that is provided to an output of the second integrator stage;
• and
• integrating, using the integrating capacitor, both an input signal provided to the current amplifier and the second analog feedback signal.

A method comprising:

• converting an analog input signal to a digital output signal using a continuous-time sigma-delta analog-to-digital converter that comprises:
• a plurality of integrator stages,
• an outer feedback loop, and
• an inner feedback loop;
• and
• reducing a delay in the inner feedback loop by providing a feedback signal of the inner feedback loop as an analog current feedback signal to an output of one of the integrator stages that comprises a current buffer and an integrating capacitor, and using the integrating capacitor to integrate the analog current feedback signal together with an input signal to the integrating stage having the current buffer and the integrating capacitor.

An apparatus comprising:

• a continuous-time sigma-delta analog-to-digital converter to convert an analog input signal to a digital output signal, the continuous-time sigma-delta analog-to-digital converter comprising:
• a plurality of integrator stages, one of the integrator stages comprising a current buffer that drives an integrating capacitor;
• an outer feedback digital-to-analog converter to provide a first feedback signal;
• and
• means for converting the digital output signal to an analog current feedback signal that is provided to an output of the integrator stage having the current buffer and the integrating capacitor, and integrating both the analog current feedback signal and an input signal provided to the integrator stage having the current buffer and the integrating capacitor.