| 摘要 |
PURPOSE:To allow the phase of a voltage-controlled oscillator to follow up the phase of data easily by measuring the period of input data through a data period measuring circuit, setting the control voltage of the voltage-controlled oscillator when a data block is detected, and then inputting the data to a phase comparing circuit. CONSTITUTION:The data period measuring circuit 1 consists of a reference oscillator, counter, flip-flop and known logical circuit, and the interval between pull- in data added to the head and tail of a data block is measured by the reference oscillator and counter. The output of the data period measuring circuit 1 is inputted to an initial value voltage setting circuit 2 and converted into a proper voltage depending upon control voltage-frequency characteristics. This output is turned on and off under the control based upon the output of a delay circuit 4. The voltage of a loop filter 7 is set to this output voltage and a phase comparing circuit 6 becomes able to operate. Then, the voltage-controlled oscillator 5 outputs an oscillation frequency corresponding to the voltage of the loop filter. |
