Power supply voltage transition comparison circuit, power supply voltage transition comparison method, and semiconductor integrated circuit

Abstract

A power supply voltage transition comparison circuit includes a comparator evaluation voltage setting circuit that generates a divided voltage of a power supply voltage; a comparator that compares a reference voltage with the divided voltage; a voltage evaluation circuit that evaluates the power supply voltage based on a result of the comparison; and an evaluation voltage setting value output circuit that changes a ratio between the power supply voltage and the divided voltage based on a result of an evaluation of the power supply voltage.

What is claimed is: 
     
         1 . A power supply voltage transition comparison circuit comprising:
 a comparator evaluation voltage setting circuit that generates a divided voltage of a power supply voltage;   a comparator that compares a reference voltage with the divided voltage;   a voltage evaluation circuit that evaluates the power supply voltage based on a result of the comparison; and   an evaluation voltage setting value output circuit that changes a ratio between the power supply voltage and the divided voltage based on a result of an evaluation of the power supply voltage.   
     
     
         2 . The power supply voltage transition comparison circuit according to  claim 1 , wherein the evaluation voltage setting value output circuit changes a voltage setting mode between an upper-limit voltage setting mode in which the ratio between the power supply voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range, and a lower-limit voltage setting mode in which the ratio between the power supply voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range based on an upper/lower selector signal output by the voltage evaluation circuit, and
 the voltage evaluation circuit determines whether or not the power supply voltage is within the expected voltage range based on an output of the comparator.   
     
     
         3 . The power supply voltage transition comparison circuit according to  claim 2 , wherein the voltage evaluation circuit secures a predetermined wait time after the voltage evaluation circuit changes the upper/lower selector signal from a value indicating one of the upper-limit voltage setting mode and the lower-limit voltage setting mode to a value indicating the other of the upper-limit voltage setting mode and the lower-limit voltage setting mode, and then determines whether the power supply voltage is lower than the upper-limit voltage or determines whether the power supply voltage is higher than the lower-limit voltage based on the output of the comparator. 
     
     
         4 . The power supply voltage transition comparison circuit according to  claim 1 , wherein the evaluation voltage setting value output circuit changes a voltage setting mode between an upper-limit voltage setting mode in which the ratio between the power supply voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range, and a lower-limit voltage setting mode in which the ratio between the power supply voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range based on an upper/lower selector signal output by the voltage evaluation circuit. 
     
     
         5 . The power supply voltage transition comparison circuit according to  claim 1 , wherein the voltage evaluation circuit determines whether or not the power supply voltage is within an expected voltage range based on an output of the comparator. 
     
     
         6 . A power supply voltage transition comparison method, comprising:
 generating a divided voltage of a power supply;   comparing a reference voltage with the divided voltage;   evaluating the power supply voltage based on a result of the comparison; and   changing a ratio between the power supply voltage and the divided voltage based on a result of an evaluation of the power supply voltage.   
     
     
         7 . The power supply voltage transition comparison method according to  claim 6 , further comprising changing, by a voltage evaluation circuit, a voltage setting mode between an upper-limit voltage setting mode and a lower-limit voltage setting mode,
 wherein:
 in the upper-limit voltage setting mode, a ratio between the power supply voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range; 
 in the lower-limit voltage setting mode, the ratio between the power supply voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range; and 
 the evaluating of the power supply voltage comprises evaluating, by the voltage evaluation circuit, whether or not the power supply voltage is within the expected voltage range based on an output of a comparator that compares the reference voltage with the divided voltage. 
   
     
     
         8 . The power supply voltage transition comparison method according to  claim 6 , further comprising changing, by a voltage evaluation circuit, a voltage setting mode between an upper-limit voltage setting mode and a lower-limit voltage setting mode. 
     
     
         9 . The power supply voltage transition comparison method according to  claim 8 ,
 wherein:
 in the upper-limit voltage setting mode, a ratio between the power supply voltage and the divided voltage is set based on an upper-limit voltage of an expected voltage range. 
   
     
     
         10 . The power supply voltage transition comparison method according to  claim 8 ,
 wherein:
 in the lower-limit voltage setting mode, the ratio between the power supply voltage and the divided voltage is set based on a lower-limit voltage of the expected voltage range; and 
 the evaluating of the power supply voltage comprises evaluating, by the voltage evaluation circuit, whether or not the power supply voltage is within the expected voltage range based on an output of a comparator that compares the reference voltage with the divided voltage. 
   
     
     
         11 . A power supply voltage transition comparison circuit, comprising:
 a comparator evaluation voltage setting circuit that generates a divided voltage based on a power supply voltage;   a comparator that compares a reference voltage with the divided voltage;   a voltage evaluation circuit that evaluates the power supply voltage based on a result of the comparison; and   an evaluation voltage setting value output circuit that outputs an evaluation voltage setting signal base on a result of the evaluation,   wherein the comparator evaluation voltage setting circuit generates the divided voltage based on the evaluation voltage setting signal.   
     
     
         12 . The power supply voltage transition comparison circuit according to  claim 11 , wherein the comparator evaluation voltage setting circuit comprises:
 a resistance voltage-dividing circuit that generates the comparison voltage by dividing the power supply voltage.   
     
     
         13 . The power supply voltage transition comparison circuit according to  claim 11 , wherein
 the comparator evaluation voltage setting circuit sets, when the evaluation voltage setting signal indicates the upper-limit voltage of an expected voltage range, the ratio so that when the power supply voltage matches the upper-limit voltage, the comparison voltage matches the reference voltage, and   the comparator evaluation voltage setting circuit sets, when the evaluation voltage setting signal indicates the lower-limit voltage of the expected voltage range, the ratio so that when the power supply voltage matches the lower-limit voltage, the comparison voltage matches the reference voltage.   
     
     
         14 . The power supply voltage transition comparison circuit according to  claim 11 , wherein
 the result of the comparison is a low level signal when the comparison voltage is lower than the reference voltage, and is a high level signal when the comparison voltage is higher than the reference voltage.   
     
     
         15 . The power supply voltage transition comparison circuit according to  claim 11 , wherein
 the result of the comparison is a low level signal when the power supply voltage is lower than the voltage indicated by the evaluation voltage setting signal, and is a high level signal when the power supply voltage is higher than the voltage indicated by the evaluation voltage setting signal, and the comparator output signal is at a high level.   
     
     
         16 . The power supply voltage transition comparison circuit according to  claim 11 , wherein
 the voltage evaluation circuit determines whether or not the power supply voltage is lower than the upper-limit voltage of the expected voltage range based on the result of the comparison in a first mode, and determines whether or not the power supply voltage is higher than the lower-limit voltage of the expected voltage range based on the comparison in a second mode.   
     
     
         17 . The power supply voltage transition comparison circuit according to  claim 13 , wherein
 the voltage evaluation circuit determines that the power supply voltage is within the expected voltage range when the power supply voltage is lower than the upper-limit voltage and higher than the lower-limit voltage.   
     
     
         18 . The power supply voltage transition comparison circuit according to  claim 16 , wherein:
 the voltage evaluation circuit outputs a mode selector signal; and   the comparator evaluation voltage setting circuit changes the voltage setting mode between the first mode and the second mode based on the mode selector signal.   
     
     
         19 . The power supply voltage transition comparison circuit according to  claim 16 , wherein
 the evaluation voltage setting value output circuit notifies the comparator evaluation voltage setting circuit of the upper-limit voltage in the first mode, and notifies the comparator evaluation voltage setting circuit of the lower upper-limit voltage in the second mode.