| 摘要 |
The present invention has a hierarchical DLL circuit comprising a rough DLL circuit for phase adjustment by rough delay unit and a fine DLL circuit for phase adjustment by smaller, fine delay unit. When phase adjustment begins, only the rough DLL circuit operates; when the rough DLL circuit locks on, phase adjustment by the rough DLL circuit ends and the delay amount of the rough DLL circuit is set. When the rough DLL circuit locks on, the fine DLL circuit is caused to operate. In this way, the phase of the timing clock generated by the DLL circuit is adjusted only by fine delay units even if the phase of the reference clock is temporarily shifted by a large amount due to power source noise or the like. Consequently, in the event of temporary phase shifting, the amount of jitter in the timing clock can be suppressed to the small amount of a fine delay unit. Phase adjustment by the rough DLL circuit is stopped by ending phase comparison by the phase comparison circuit, or ending the input of the clock to the phase comparison circuit, for example.
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