| 摘要 |
In a clock shaping circuit, a phase comparator 31, a selector 76, a loop filter 2, and a VCSO/VCXO 4 form a PLL circuit's main feedback loop during normal operation. When the main feedback loop of the PLL circuit malfunctions due to unlocking, a quartz crystal oscillator circuit is used, and a PLL circuit's backup feedback loop is established, which includes a backup phase comparator 74, the selector 76, the loop filter 2, and the VCSO/VCXO 4.
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