| 摘要 |
The present invention provides an input interruption detecting circuit of an optical receiver that realizes a circuit structure that avoids erroneous synchronization due to an influence of a synchronous noise, and enables an accurate detection of an input interruption, with respect to input interruption detection based on the synchronous or asynchronous state of a PLL circuit. To this end, the input interruption detecting circuit of an optical receiver according to the invention is one which is provided with a noise superimposition section which superimposes an asynchronous noise having frequency components that make the PLL circuit asynchronous, onto a signal input to a phase comparator of the PLL circuit, in a circuit structure for performing input interruption detection based on the synchronous state of a PLL circuit. As a result, at the time of an input interruption of the optical signal, the PLL circuit is hardly influenced by the synchronous noise, and it enters an asynchronous state due to the influence of the asynchronous noise, thus enabling accurate input interruption detection.
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