| 摘要 |
A clock switching circuit is provided for switching from a first clock signal being output to a freely selected second clock signal among a plurality of clock signals having different frequencies and phases while preventing generation of a hazard. The switching circuit has a plurality of unit circuits for respectively receiving as an input the clock signals, selection signals of the clock signals and enabling signals and controls supplying and stopping of the clock signals in accordance with the selection signals and the enabling signals. A feedback circuit monitors output conditions of the plurality of unit circuits and, when outputting of all clock signals of the plurality of unit circuits was stopped as a result of stopping the first clock signal, giving a plurality of the unit circuits the enabling signal for approving starting of a supply of the second clock signal.
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