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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
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如果是由OR(或)、AND(与)和其它门组成的多输入组合逻辑,输入信号变化时序的微小差异会导致短暂的须状脉冲,这即是所谓的危害。
使用下图所示的电路,让我们看一下危险是如何因信号延迟的差异而发生的。假设A和B同时发生信号上升沿。施加到B的信号通过反相器到达AND(与)门。由于从B进入AND(与)门的信号因反相器而延迟,AND(与)门将在不同的时序接收到输入信号A和C,所以可能会在Y输出处产生高脉冲。
危害的对策
组合逻辑的设计应确保避免从输入的同步变化产生所需的输出值。使用触发器调整输出时序也有助于消除危害。
除了信号时序差异外,缓慢变化的输入也可能导致危害。
使用带有施密特触发器输入的逻辑门,可以防止因缓慢变化的输入引起的危害。