| 摘要 |
PURPOSE:To reduce the of influence noise generated in a power wire onto other circuit without decreasing operating speed by constituting the titled circuit by two power terminal pairs, two buffer circuits connected respectively to them, the common output terminal of the buffer circuits, a means detecting an output signal, and a control means receiving the detected output and operating the buffer circuits in response to the input signal. CONSTITUTION:A control circuit 18 operates one buffer circuit 15 only when the level of a signal IN to be outputed externally from an IC changes to set the level of an output signal OUT and operates the other buffer circuit 16 only after the signal OUT reaches the threshold value of a signal detection circuit 20 after the setting. Thus, when the level of the signal IN changes, only one buffer circuit 15 is operated in response to the output of the control circuit 18 thereby setting the level of the output signal OUT. Thus, in such case, a noise is caused between power supply VDD1 and VSS1. Since the other circuit 16 is inoperative, no noise is caused between power supply VDD2 and VSS. In changing the level of the output signal OUT, since the output terminal 17 is sufficiently driven by the circuit 15, the speed of the signal OUT does not slow down.
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