Patent ID: 7750741

Claim:
A phase locked loop circuit comprising: a phase comparator configured to receive an input signal and a feedback signal; a charge pump controlled by an output of the phase comparator; a lowpass filter part configured to receive an output of the charge pump; a current controlled oscillator controlled by a current output from the lowpass filter part; and a frequency divider configured to frequency-divide an output of the current controlled oscillator and to output the feedback signal, said lowpass filter part comprising: an amplifier part including an amplifier having an inverting input terminal and a non-inverting input terminal, and configured to receive the output of the charge pump by the inverting input terminal and a reference voltage by the non-inverting input terminal; and a circuit part configured to receive the output of the charge pump and an output of the amplifier, said circuit part including first and second capacitors having first terminals coupled to a first node that couples the output of the charge pump and the inverting input terminal of the amplifier, and first and second resistors having first terminals coupled to a second node that couples to the output of the amplifier, wherein the first resistor has a second terminal coupled to a second terminal of the first capacitor, the second capacitor has a second terminal coupled to the second node, and the second resistor has a second terminal that is grounded, said amplifier part further including a current mirror circuit coupled to the output of the amplifier and configured to supply a current which is larger than 0 and is output from the lowpass filter part to the current controlled oscillator, wherein a current flowing from the charge pump to the first node and a current flowing from the first node to the charge pump are maintained the same.