| CPC H03L 5/02 (2013.01) [H03K 17/223 (2013.01)] | 9 Claims |

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8. A power down method, comprising:
holding a first power signal to generate a second power signal;
comparing the first power signal and the second power signal to generate a comparison result on determining whether the first power signal is dropped to be lower than a first threshold voltage; and
holding the second power signal to be greater than a second threshold voltage for a predetermined time length after the first power signal is dropped to be lower than the first threshold voltage.
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