A/D converter input stage providing high linearity and gain matching between multiple channels
An input stage for an A/D converter includes a transconductance element adapted to receive, at a first input of the transconductance element, an analog input signal that is to be converted to a digital signal by the A/D converter, a feedback path for providing an analog feedback signal to a second input of the transconductance element, the analog feedback signal being based on a digital output signal of the A/D converter, and an integrator for integrating an output current of the transconductance element, wherein the integrating element is adapted to generate an integrator output signal representative of the integrated output current. The input stage may be included in an A/D converter. A plurality of such A/D converters may be included in a system.
1. An input stage for an A/D converter of differential analog signals, the input stage comprising
a transconductance element adapted to receive, at a first input of the transconductance element, an analog input signal of the differential analog signals that is to be converted to a digital signal by the A/D converter,
a feedback path for providing an analog feedback signal to a second input of the transconductance element, the analog feedback signal being based on a digital output signal of the A/D converter,
an integrator for integrating an output current of the transconductance element, wherein the integrating element is adapted to generate an integrator output signal representative of the integrated output current,
a further transconductance element adapted to receive, at a first input of the further transconductance element, the other analog input signal of the differential analog signals, and
a further feedback path for providing a further analog feedback signal to a second input of the further transconductance element, the further analog feedback signal being based on the digital output signal of the A/D converter,
wherein the integrator is adapted to integrate a sum of the output current of the transconductance element and the output current of the further transconductance element, and wherein the integrator output signal is representative of the integrated sum of output currents.
2. An A/D converter, comprising
an input stage according to claim 1 ,
a quantizing stage adapted to receive the integrator output signal and to generate a digital output signal, and
a feedback D/A converter adapted to generate the analog feedback signal by converting the digital output signal to an analog signal and to feed the analog feedback signal to the feedback path.
3. The A/D converter according to claim 2 , wherein the feedback D/A converter comprises a resistive ladder structure.
4. A system comprising a plurality of A/D converters according to claim 2 , wherein the feedback D/A converters of the plurality of A/D converters share a resistive ladder structure.
5. The input stage according to claim 1 , further comprising
a chopper arranged between the output of the transconductance element and the integrator, the chopper being operable to reverse a polarity of the output of the transconductance element.
6. The input stage according to claim 1 , wherein the integrator comprises a capacitor, wherein the integrator output signal is a voltage across the capacitor, and wherein an output of the transconductance element and an output of the further transconductance element are applied to terminals of the capacitor.
7. The input stage according to claim 1 , wherein the first input of the transconductance element and the first input of the further transconductance element have opposite polarity.
8. The A/D converter according to claim 1 , further comprising a filtering stage interposed between the input stage and the quantizing stage.
9. An A/D converter of differential analog signals, comprising;
an input stage for the A/D converter, the input stage including,
a transconductance element adapted to receive, at a first input of the transconductance element, an analog input signal of the differential analog signals that is to be converted to a digital signal by the A/D converter,
a feedback path for providing an analog feedback signal to a second input of the transconductance element, the analog feedback signal being based on a digital output signal of the A/D converter, and
an integrator for integrating an output current of the transconductance element, wherein the integrating element is adapted to generate an integrator output signal representative of the integrated output current;
a further transconductance element adapted to receive, at a first input of the further transconductance element, the other analog input signal of the differential analog signals,
a further feedback path for providing a further analog feedback signal to a second input of the further transconductance element, the further analog feedback signal being based on the digital output signal of the A/D converter;
wherein the integrator is adapted to integrate a sum of the output current of the transconductance element and the output current of the further transconductance element, and wherein the integrator output signal is representative of the integrated sum of output currents; and
a chopper arranged between the output of the transconductance element and the integrator, the chopper being operable to reverse a polarity of the output of the transconductance element;
a quantizing stage adapted to receive the integrator output signal and to generate a digital output signal, and
a feedback D/A converter adapted to generate the analog feedback signal by converting the digital output signal to an analog signal and to feed the analog feedback signal to the feedback path,
wherein the chopper is further operable to switch between a differential mode of operation and a common mode of operation by reversing the polarity of the output of the transconductance element.