| 摘要 |
PROBLEM TO BE SOLVED: To prevent malfunction of circuits due to a metastable state brought about in a synchronization circuit. SOLUTION: When a DFF 1 becomes the metastable state to make a Q output a vibration state, Q output terminals of DFFs 2 and 3 both become H while an ouput Q of the DFF 1 vibrates by one period. Consequently, an output terminal of an AND gate 7 becomes H, prohibiting writing of a DFF 5-2. At the same time, a BD signal of a DATA_IN terminal 21 is latched by a DFF 5-1 at a rise of a next CLK through an AND gate 8. Moreover, an H signal of the AND gate 7 is latched by a DFF 4, and the DFFs 2 and 3 are reset. Along with this, an output of a selector consisting of gates 9, 10 and 11 is changed over to a Q output of the DFF 5-1. Accordingly, a Q output signal of the DFF 5-1 is connected to a D input terminal of a DFF 6, and an output signal of a Q terminal of the DFF 5-1 is latched by the DFF 6 at a rise of a next CLK. COPYRIGHT: (C)2005,JPO&NCIPI
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