Phase locked loop circuit including automatic frequency control circuit and operating method thereof

A Phase Locked Loop (PLL) circuit comprising:

• a voltage controlled oscillator outputting a signal having an arbitrary frequency;
• a loop filter outputting a control voltage for controlling a frequency of a signal outputted from the voltage controlled oscillator;
• a regulator supplying a power source voltage to the voltage controlled oscillator;
• and
• an automatic frequency control circuit receiving a signal having a reference frequency and a divided signal of an output signal of the voltage controlled oscillator, and generating a control code for controlling the power source voltage outputted from the regulator,
• wherein the voltage controlled oscillator is primarily controlled by the power source voltage supplied from the regulator, is secondarily controlled by a control voltage of the loop filter, and generates an output signal synchronized with a target frequency.

An operating method of a Phase Locked Loop (PLL) circuit, the operating method comprising:

• receiving a signal having a reference frequency and an output signal of a voltage controlled oscillator, and generating pulse width signal each of the two received signals;
• converting the generated pulse width signals into voltage signals, respectively;
• comparing levels of the converted voltage signals;
• generating a control code according to the compared result;
• receiving the signal having the reference frequency and the output signal of the voltage controlled oscillator, and generating a control voltage according to a phase difference between the two received signals;
• and
• generating an output signal synchronized with a target frequency, in response to the control code and the control voltage.