| 摘要 |
PURPOSE: A PLL(Phase Locked Loop) circuit using a VCO(Voltage Controlled Oscillator) for setting a frequency is provided to form the PLL circuit with a single chip by using a control bit of the PLL to correct automatically the frequency. CONSTITUTION: A PLL circuit using a VCO for setting a frequency includes a phase detection unit, a loop filter, and a VCO. The phase detection unit(11) compares periodically an external clock signal with an internal clock signal and generates an output signal according to a phase difference between the external clock signal and the internal clock signal. The loop filter(12) is used for outputting a constant voltage according to the output signal of the phase detection unit. The VCO(13) is used for outputting the internal clock signal having a frequency proportional to the constant voltage of the loop filter. The VCO includes a capsule for controlling a value of capacitance to set the frequency of the internal clock signal by using an internal setup value.
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