Voltage drop measurement circuit

1. A voltage drop measurement circuit, comprising:

a voltage drop circuit configured to generate an output voltage and fluctuate the output voltage according to a fluctuation of a power supply voltage, a voltage difference between the output voltage and the power supply voltage being maintained by a predetermined amount; and

a flip-flop configured to retain a flag indicating a drop of the power supply voltage according to the output voltage.

2. The voltage drop measurement circuit according to claim 1 , wherein the voltage drop circuit changes a value of the output voltage according to an external input signal.

3. The voltage drop measurement circuit according to claim 2 , wherein the flip-flop includes an input voltage threshold to evaluate a level of an input signal and the input voltage threshold fluctuates according to the fluctuation in the power supply voltage.

4. The voltage drop measurement circuit according to claim 1 , wherein the voltage drop circuit generates the output voltage, the output voltage being a voltage dividing the power supply voltage by a predetermined division ratio.

5. The voltage drop measurement circuit according to claim 4 , wherein the voltage drop circuit changes the division ratio according to an external input signal.

6. The voltage drop measurement circuit according to claim 4 , wherein the flip-flop includes an input voltage threshold to evaluate a level of an input signal and the input voltage threshold fluctuates according to the fluctuation in the power supply voltage.

7. The voltage drop measurement circuit according to claim 5 , wherein the flip-flop includes an input voltage threshold to evaluate a level of an input signal and the input voltage threshold fluctuates according to the fluctuation in the power supply voltage.

8. The voltage drop measurement circuit according to claim 1 , wherein the flip-flop includes an input voltage threshold to evaluate a level of an input signal and the input voltage threshold fluctuates according to the fluctuation in the power supply voltage.

9. A voltage drop measurement circuit, comprising:

a voltage drop circuit to generate an output voltage and fluctuate the output voltage according to a fluctuation of a power supply voltage, the output voltage being the power supply voltage dropped by a predetermined amount; and

a flip-flop to retain a flag indicating a drop of the power supply voltage according to the output voltage,

wherein the flip-flop includes an input voltage threshold to evaluate a level of an input signal and the input voltage threshold fluctuates according to the fluctuation in the power supply voltage, and

wherein the input voltage threshold and the output voltage fluctuate at different sensitivities for the fluctuation in the power supply voltage.

10. A semiconductor device comprising a plurality of voltage drop measurement circuits, wherein each of the plurality of voltage drop measurement circuits include the voltage drop measurement circuit of claim 1 .

11. A voltage drop measurement circuit, comprising:

a voltage drop circuit which generates an output voltage that fluctuates based on a power supply voltage; and

a detector which has a threshold voltage and which determines a drop of the power supply voltage by inversing a voltage difference between the output voltage and the threshold voltage,

wherein the threshold voltage fluctuates based on the power supply voltage, the output voltage fluctuates more widely when the power supply voltage fluctuates than the threshold voltage.

12. The voltage drop measurement circuit according to claim 11 , wherein the detector detects the drop of the power supply voltage for each cycle of a clock signal.

13. The voltage drop measurement circuit according to claim 11 , wherein the voltage drop circuit includes a constant voltage circuit and at least two resistors, the constant voltage circuit is coupled to the power supply voltage, the resistors are coupled in parallel with the constant voltage circuit, and the output voltage is voltage of a joint of the resistors.

14. The voltage drop measurement circuit according to claim 13 , wherein the resistors change the resistance value according to a control signal.

15. The voltage drop measurement circuit according to claim 11 , wherein the voltage drop circuit includes a constant voltage circuit, a transistor and a resistor, the constant voltage circuit is coupled to the power supply voltage, the transistor is coupled between the constant voltage circuit and the resistor, and the output voltage is voltage of a joint of the transistor and the resistor.