Delta-sigma analog-to-digital converter topology with improved distortion performance

Abstract

A delta-sigma Analog-to-Digital Converter (ADC) (IC) which includes an input feed-forward path extending from an input to the ADC to a feed-forward summing circuit disposed between a loop filter and quantizer of the ADC, and a filter disposed in the feed-forward path as an apparatus for improving distortion performance in the delta-sigma ADC. The filter may be a low pass filter, for example, a Resistor-Capacitor (RC) circuit. The filter may have a cut-off frequency outside the ADC's passband. The filtering provided may be continuous-time filtering, even if the delta-sigma ADC is a discrete-time delta-sigma ADC.

What is claimed is: 
     
         1 . A method for operating a discrete-time delta-sigma analog-to-digital converter (DT-DSADC) comprising:
 filtering, by a continuous-time filter, an input signal at an input terminal of the DT-DSADC, the continuous-time filter disposed in a feed-forward path of the DT-DSADC, the feed-forward path extending from the input terminal to a feed-forward summing circuit disposed between a discrete-time loop filter and a quantizer of the DT-DSADC; and   sampling, by a feed-forward sampler, the filtered input signal, the feed-forward sampler disposed after the continuous-time filter in the feed-forward path of the DT-DSADC.   
     
     
         2 . The method of  claim 1 , wherein the continuous-time filter is disposed before the feed-forward sampler for reducing kickback due to the sampling of the filtered input signal by the feed-forward sampler. 
     
     
         3 . The method of  claim 1 , wherein the continuous-time filter is a low pass filter. 
     
     
         4 . The method of  claim 3 , wherein the low pass filter is a resistor-capacitor circuit. 
     
     
         5 . The method of  claim 3 , wherein the continuous-time filter has a cut-off frequency outside of a passband of the DT-DSADC, the passband including a range of frequencies corresponding to input signals of the DT-DSADC. 
     
     
         6 . The method of  claim 1 , wherein the discrete-time delta-sigma analog-to-digital converter is an integrated circuit. 
     
     
         7 . A discrete-time delta-sigma analog-to-digital converter (DT-DSADC), the apparatus comprising:
 a continuous-time filter disposed in a feed-forward path of the DT-DSADC, the feed-forward path extending from an input terminal of the DT-DSADC to a feed-forward summing circuit, the feed-forward summing circuit disposed between a discrete-time loop filter and a quantizer of the DT-DSADC; and   a feed-forward sampler disposed after the continuous-time filter in the feed-forward path of the DT-DSADC.   
     
     
         8 . The apparatus discrete-time delta-sigma analog-to-digital converter of  claim 7 , wherein the continuous-time filter is disposed before the feed-forward sampler for reducing kickback due to the sampling of the filtered input signal by the feed-forward sampler. 
     
     
         9 . The discrete-time delta-sigma analog-to-digital converter of  claim 7 , wherein the discrete-time loop filter includes a cascade of integrators. 
     
     
         10 . The discrete-time delta-sigma analog-to-digital converter of  claim 7 , wherein the continuous-time filter is a low pass filter. 
     
     
         11 . The discrete-time delta-sigma analog-to-digital converter of  claim 10 , wherein the low pass filter is a resistor-capacitor circuit. 
     
     
         12 . The discrete-time delta-sigma analog-to-digital converter (DT-DSADC) of  claim 10 , wherein the low pass filter has a cut-off frequency outside of a passband of the DT-DSADC, the passband including a range of frequencies corresponding to input signals of the DT-DSADC. 
     
     
         13 . The discrete-time delta-sigma analog-to-digital converter (DT-DSADC) of  claim 7 , wherein the DT-DSADC is an integrated circuit.