Semiconductor device with voltage variation detector

1. A semiconductor device, comprising:

a capacitance element having one end connected to a power supply, the capacitance element for detecting a voltage variation of the power supply;

a first comparator having two input nodes having opposite polarities to each other, a first input node of the two input nodes for receiving a reference voltage and a second input node of the two input nodes connected to an output of the other end of the capacitance element to compare the respective voltage values to output a first output signal indicating a comparison result, such that the capacitance element is connected in series with the power supply and the second input node;

a first resistor element connecting the first input node and the second input node of the first comparator;

a second resistor element having a first end directly connected to said power supply;

a third resistor element having a first end connected to a second end of the second resistor and having a second end directly connected to a ground terminal;

a second comparator having two input nodes directly connected to the first end of the third resistor element and the reference voltage terminal, respectively, and for outputting a second output signal indicating a second comparison result;

a logic OR circuit which performs a logic OR operation of the first output signal of the first comparator and the second output signal of the second comparator; and

a reset circuit for receiving an output signal of the logic OR circuit, and for halting operation of a system including the semiconductor device when the output signal of the OR circuit is activated;

wherein the first comparator is for outputting a first output signal indicating the comparison result when a predetermined voltage difference exists between the inputted reference voltage and the inputted output of the other end of the capacitance element.

2. A semiconductor device as defined in claim 1 , wherein:

the first comparator is a hysteresis comparator for outputting the first output signal indicating the first comparison result when the voltage difference between the inputted reference voltage and the output of the other end of the capacitance element becomes larger than a predetermined hysteresis width.

3. A semiconductor device as defined in claim 1 , further comprising a switching part for switching a value of the output of the other end of the capacitance element to an arbitrary value.

4. A semiconductor device as defined in claim 3 , further comprising a control section which operates the switching part at turning on the power of the semiconductor device.

5. A semiconductor device comprising:

a first capacitance element and a second capacitance element, one end of each of which is connected to a separate power supply, the first and second capacitance elements for detecting a voltage variation of each power supply;

a first comparator having input nodes, the input nodes having opposite polarities and receiving a reference voltage and an output of the other end of the first capacitance element at their inputs to compare the respective voltage values to output a first signal indicating a first comparison result;

a second comparator which has two input nodes, the input nodes having opposite polarities and receiving a reference voltage and an output of the other end of the second capacitance element at their inputs to compare the respective voltage values to output a second signal indicating a second comparison result;

a first resistor element and a second resistor element each of which connects the one side input node and the other side input node of the first and the second comparators, respectively;

a logic OR circuit for performing a logic OR operation of the first output signal of the first comparator and the second output signal of the second comparator;

wherein the first and the second comparators output the first and second output signals, respectively, when a voltage difference is detected between inputted reference voltage and the inputted output of the other end of the respective first and second capacitance element, and

the polarity of the input node which receives the output of the other end of the first capacitance element in the first comparator and the polarity of the input node which receives an output of the other end of the second capacitance element in the second comparator are opposite to each other.

6. A semiconductor device as defined as defined in claim 5 wherein:

the first comparator and the second comparator are hysteresis comparators which output the first and second output signals indicating the respective comparison results when a voltage difference between the inputted reference voltage and the inputted output of the other end of the first and second capacitance element, respectively, is larger than a predetermined hysteresis width.