Patent ID: 8232848
Filing Date: 2012-07-31
Classification: H03F

Abstract:
1. A semiconductor integrated circuit device comprising: a ring oscillator circuit that includes a plurality of cascaded differential amplifier circuits; wherein the differential amplifier circuits each include: a first transistor that operates in accordance with a potential difference between a first supply voltage node and a second supply voltage node, serves as one of a pair of differential input transistors, and is configured by coupling the gate thereof to a positive differential input node, a second transistor that serves as the remaining one of the pair of differential input transistors and is configured by coupling the gate thereof to a negative differential input node, a first limit transistor that uses a path between the first supply voltage node and the positive differential input node as a source-drain path, a second limit transistor that uses a path between the first supply voltage node and the negative differential input node as a source-drain path, a first gate control circuit that controls the gate of the first limit transistor, and a second gate control circuit that controls the gate of the second limit transistor; and wherein the first gate control circuit and the second gate control circuit have a first operation mode, in which the first gate control circuit causes the first limit transistor to function as a first diode for limiting the signal amplitude of the positive differential input node to a threshold voltage thereof, and the second gate control circuit causes the second limit transistor to function as a second diode for limiting the signal amplitude of the negative differential input node to a threshold voltage thereof.