| 摘要 |
A clock switching circuit comprises PLL circuits into which external clocks CLKT, CLKB are respectively input, a multiplexer for selecting and outputting either an output PLB of one PLL circuit or an inverted signal of an output PLT of the other PLL circuit, and a clock control circuit for subjecting the multiplexer to switching control on the basis of a Lock determination signal that is asynchronous with CLKB and PLB. When the Lock determination signal is input into the clock control circuit, the clock control circuit switches the output of the multiplexer in synchronization with an offset clock PLQB that is offset from the phase of PLB by a predetermined value.
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