Analog-to-digital converter

Abstract

An analog-to-digital converter includes an input terminal, a digital-to-analog converter, a comparator, and successive approximation circuitry. The input terminal is configured to receive a multi-bit digital threshold value from circuitry external to the analog-to-digital converter. The successive approximation circuitry is coupled to the comparator and the digital-to-analog converter. The successive approximation circuitry is configured to operate in a comparison mode and a conversion mode, and to provide the multi-bit digital threshold value to the digital-to-analog converter while operating in the comparison mode. The comparator is coupled to the digital-to-analog converter and the successive approximation circuity. The comparator is configured to output a signal that indicates whether an analog input signal exceeds an analog threshold signal corresponding to the multi-bit digital threshold value.

What is claimed is: 
     
         1 . An analog-to-digital converter, comprising:
 an input terminal configured to receive a multi-bit digital threshold value from circuitry external to the analog-to-digital converter;   a digital-to-analog converter;   successive approximation circuitry coupled to the digital-to-analog converter, the successive approximation circuitry configured to:
 operate in a comparison mode and a conversion mode; and 
 provide the multi-bit digital threshold value to the digital-to-analog converter while operating in the comparison mode; and 
   a comparator coupled to the digital-to-analog converter and the successive approximation circuity, the comparator configured to output a signal that indicates whether an analog input signal exceeds an analog threshold signal corresponding to the multi-bit digital threshold value.   
     
     
         2 . The analog-to-digital converter of  claim 1 , wherein the digital-to-analog converter is a capacitive digital-to-analog converter comprising:
 a plurality of capacitors; and   a plurality of switches coupled to each of the capacitors; and   wherein the successive approximation circuitry is configured to set the switches according to bits of the multi-bit digital threshold value while operating in the comparison mode.   
     
     
         3 . The analog-to-digital converter of  claim 2 , wherein the successive approximation circuitry is configured to apply the output signal generated by the comparator to determine whether each of the switches is to be opened or closed while operating in the conversion mode. 
     
     
         4 . The analog-to-digital converter of  claim 1 , wherein the successive approximation circuitry is configured to disregard the output signal generated by the comparator while operating in the comparison mode. 
     
     
         5 . The analog-to-digital converter of  claim 1 , wherein the successive approximation circuitry is configured to disregard the multi-bit digital threshold value while operating in the conversion mode. 
     
     
         6 . The analog-to-digital converter of  claim 1 , wherein the successive approximation circuitry is configured to execute a binary search for a digital value corresponding to a voltage of an analog input signal while operating in the conversion mode. 
     
     
         7 . A measurement system, comprising:
 an analog multiplexer; and   a successive approximation register analog-to-digital converter coupled to an output of the analog multiplexer, the successive approximation register analog-to-digital converter configured to operate in a comparison mode and a conversion mode; wherein:
 in the comparison mode, the successive approximation register analog-to-digital converter is configured to:
 convert a multi-bit digital threshold value received from circuitry external to the successive approximation register analog-to-digital converter to an analog threshold signal; and 
 compare a signal received from the analog multiplexer to the analog threshold signal.