Patent ID: 7271670

Claim:
A CR oscillation circuit comprising: a first logic element having an input terminal connected to a first node and an output terminal connected to a second node; a second logic element having an input terminal connected to the second node and an output terminal connected to a third node; a capacitive element connected between the first node and the second node in parallel with the first logic element; and a resistive element connected between the first node and the third node in parallel with the first and second logic elements, wherein the capacitive element includes a well formed in a semiconductor substrate, a diffusion layer formed in the well, the diffusion layer being electrically connected to any one of the first node and the second node, a gate electrode formed on the well and the diffusion layer, the gate electrode being electrically connected to the other one of the first node and the second node, and a gate oxide film formed between the well and the gate electrode, each of the first and second logic elements has a voltage-dependence characteristic such that its on-resistance varies according to a variation in a supply voltage, the capacitive element has a voltage-dependence characteristic such that its capacitance value varies according to the variation in the supply voltage, and a capacitance value of the capacitive element decreases when the on-resistance of the first and second logic elements increases according to the variation in the supply voltage, and wherein a variation amount of the capacitance value of the capacitive element which is determined according to a variation amount of the supply voltage is increased or decreased by forming at least one opening in the gate electrode.