Technique for comparing analog signal with reference voltage

Abstract

The present invention provides a technique for reducing power consumption of an A/D converting device. An A/D converting device according to the present invention includes: multiple comparators each of which has a function for comparing input analog signals with a predetermined reference voltage; an A/D converter for converting the input analog signal into the digital signal with a predetermined number of bits using comparison results from the multiple comparators; a determining unit for determining which range the voltage of the input analog signal belongs to before the comparators comparing the input analog signal with the reference voltages; and a control unit for controlling power supply for the multiple comparators corresponding to the range determined by the determining unit. Thus, power is supplied only to the comparators necessary for this particular A/D conversion, thereby reducing power consumption.

1 - 2 . (canceled)  
   
   
       3 . A comparing device, comprising a plurality of comparators for comparing input analog signals with predetermined reference voltages, 
 wherein the conceivable range of the voltage of said input analog signal is divided into a plurality of ranges with predetermined thresholds as boundaries,    and wherein said reference voltages, which belong to different ranges, are changed such that the reference voltage belonging to the range which the voltage of said input analog signal belongs to is input to said plurality of comparators.    
   
   
       4 . A comparing device according to  claim 3 , further comprising: 
 a determining unit for determining which range the voltage of said input analog signal belongs to; and    a switching unit for changing said reference voltages input to said plurality of comparators corresponding to the range determined by said determining unit,    wherein said switching unit changes said reference voltages such that the range between the maximum value and the minimum value of said reference voltages input to said plurality of comparators covers said range determined by said determining unit.    
   
   
       5 . (canceled)  
   
   
       6 . An analog/digital converting device comprising: 
 an A/D converter including a plurality of comparators each of which compares input analog signals with a predetermined reference voltage, for converting an input analog signal into a digital signal with a predetermined number of bits using comparison results from said plurality of comparators;    a determining unit for determining which range the voltage of said input analog signal belongs to, before said comparators comparing said input analog signal with said reference voltages, with regard to a plurality of ranges into which the conceivable range of the voltage of said input analog signal is divided with predetermined thresholds as boundaries; and    a switching unit for changing said reference voltages, which belong to different ranges, such that the reference voltage belonging to the range determined by said determining unit it input to said plurality of comparators.    
   
   
       7 . An analog/digital converting device according to  claim 6 , wherein said A/D converter includes a smaller number of comparators than those required for forming an A/D converter having a function for converting said input analog signal into said digital signal with the predetermined number of bits, 
 and wherein at least one of said plurality of comparators is operated so as to compare said input analog signal with plurality kinds of reference voltages by switching said reference voltage.    
   
   
       8 . (canceled)  
   
   
       9 . An analog/digital converting device according to  claim 6 , comprising a plurality of conversion units each of which includes: 
 said A/D converter;    a D/A converter for converting the output from said A/D converter into the analog signal;    a subtracter for subtracting the output signal from said D/A converter, from said input analog signal; and    an amplifier for amplifying the output signal from said subtracter,    wherein said determining unit is provided for each of said conversion units.    
   
   
       10 . An analog/digital converting device according to  claim 7 , comprising a plurality of conversion units each of which includes: 
 said A/D converter;    a D/A converter for converting the output from said A/D converter into the analog signal;    a subtracter for subtracting the output signal from said D/A converter, from said input analog signal; and    an amplifier for amplifying the output signal from said subtracter,    wherein said determining unit is provided for each of said conversion units.    
   
   
       11 . (canceled)  
   
   
       12 . An analog/digital converting device according to  claim 9 , wherein at least one of said plurality of conversion units includes a switching unit for switching whether the output signal from said amplifier within the same conversion unit is input as said input analog signal, or the output signal from a circuit other than the conversion unit is input as said input analog signal.  
   
   
       13 . An analog/digital converting device according to  claim 10 , wherein at least one of said plurality of conversion units includes a switching unit for switching whether the output signal from said amplifier within the same conversion unit is input as said input analog signal, or the output signal from a circuit other than the conversion unit is input as said input analog signal.  
   
   
       14 - 19 . (canceled)  
   
   
       20 . A comparison method for analog signals comprising: 
 determining which range the voltage of the input analog signal belongs to, before a plurality of comparators comparing said input analog signal with reference voltages, with regard to a plurality of ranges into which the conceivable range of the voltage of said input analog signal is divided with said thresholds as boundaries; and    changing said reference voltages, which belong to different ranges, such that the reference voltage belonging to the range determined in said determining is input to said plurality of comparators.