LSI DEVICE EQUIPPED WITH NOISE COUNTERMEASURE CIRCUIT

PURPOSE:To interrupt a noise invaded to a clock system circuit by using a sense amplifier connected to an input of a clock system circuit output buffer so as to detect a transient state by an output noise of the clock system circuit, allowing a pulse generator to generate a trigger pulse based on the detection signal and using the trigger pulse to bring the output of a tri-state circuit provided to the input side of the clock system circuit into a high impedance state for a comparatively short time. CONSTITUTION:The sense amplifier SA detects the change in the trailing from H to L level or the leading from L to H level appearing at the input by the switching operation of an output buffer circuit OB, that is, the transient edge and a pulse generating circuit PG generates a trigger starting a tri-state buffer TS by the detection signal. The tri-state buffer uses the trigger to bring the output into a high impedance state (blanking state) for a prescribed period only so as to prevent a flip-flop FF of the next stage from receiving a spike noise. That is, the invasion of noise is shut off.