| 摘要 |
A phase locked loop includes a phase-frequency detector and a loop filter. The phase-frequency detector compares phases of an input signal and a feedback signal to generate first and second control signals. The loop filter includes a pull-up resistor, a pull-down resistor and a capacitance unit. The loop filter receives a first reference voltage to charge the capacitance unit through a path formed by the pull-up resistor to the capacitance unit, receives a second reference voltage to discharge the capacitance unit through a path formed by the pull-down resistor to the capacitance unit and outputs a control voltage generated based on a charge amount of the charged capacitance unit. Therefore, the phase locked loop can operate at a relatively low voltage and can operate based on a control voltage with a wide input range.
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