Patent ID: 7504865

Claim:
A frequency sensor including: a first conductivity type MOS transistor having a gate to which an input clock signal is applied, and a source connected to a first power supply voltage; a second conductivity type MOS transistor having a gate to which the input clock signal is applied, and a source connected to a second power supply voltage; a resistor connected between drains of said first and second MOS transistors; and a capacitor connected between the drain of said first MOS transistor and said second power supply voltage; an inverter having an input terminal connected to a connection node of said capacitor and said resistor; and a third conductivity type MOS transistor having a gate connected to an output terminal of said inverter, a drain connected to the input terminal of said inverter, and a source connected to the second power supply voltage; wherein a frequency of the input clock signal is detected by an output signal of the inverter.