Phase frequency synchronism circuitry and optical receiver

Abstract

In order to solve the problem that since a loop filter constant suitable for asynchronous state cannot be selected in the conventional phase frequency synchronism circuit, it takes a long time to synchronize the input data and the clock signal from the asynchronous state, the present invention is to propose a phase frequency synchronism circuit including a phase comparator for generating a voltage according to the phase difference of the clock signal to the input signal, a frequency comparator for deciding if the frequency of the clock signal is higher or lower than the transmission rate of the input signal and generating a binary signal, a synchronous identifying unit for deciding if the input signal and the clock signal are synchronized in their phases and frequencies, a first switch that receives the output from the phase comparator and is closed and opened when the synchronous identifying unit decides that they are synchronized and not synchronized, respectively, a second switch that receives the output from the frequency comparator and is opened and closed when the synchronous identifying unit decides that they are synchronized and not synchronized, respectively, a loop filter that receives the outputs from the first and second switches, and a voltage controlled oscillator that oscillates on the basis of the output from the loop filter.

Dependencies are inferred from the claim text.