1.  Field
Exemplary embodiments of the inventive concept relate to a phase-locked-loop (PLL) circuit, and more particularly, to a PLL circuit including a digital filter. 
2.  Description of the Related Art
A phase-locked-loop (PLL) circuit may be used to synchronize the frequency of an input clock signal with that of an output clock signal to be used in an internal circuit. 
In recent years, a digital-type PLL circuit has widely been employed.  However, since the digital-type PLL circuit controls operations digitally, the digital-type PLL circuit has poor jitter noise characteristics.