Patent ID: 7463100

Claim:
A phase frequency detector for comparing a reference frequency with a division frequency created by dividing an output frequency of a voltage controlled oscillator (VCO) by a predetermined division ratio, creating a phase-difference signal corresponding to a phase difference between the reference frequency and the division frequency, and improving noise characteristics, the phase frequency detector comprising: a first phase frequency detector for receiving the reference frequency and the division frequency, creating a first phase-difference signal corresponding to a phase difference between the received reference and division frequencies, and having nonlinearity if the phase difference between the reference and division frequencies is in a first range; a second phase frequency detector for receiving the reference frequency and the division frequency, creating a second phase-difference signal corresponding to a phase difference between the received reference and division frequencies, and having nonlinearity if the phase difference between the reference and division frequencies is in a second range different from the first range; and a signal selection unit for generating the second phase-difference signal if the phase difference between the reference and division frequencies is in the first range, and generating the first phase-difference signal if the phase difference between the reference and division frequencies is in the second, wherein the signal selection unit includes: a window detector for determining any one of the first range and the second range to be a window, and determining whether the phase difference between the reference frequency and the division frequency is contained in the window; and a signal selector for selecting a phase-difference signal having nonlinearity within a range different from that of the window if the phase difference between the reference frequency and the division frequency is contained in the window, selecting a phase-difference signal having nonlinearity within the window if the phase difference between the reference frequency and the division frequency is not contained in the window, and outputting the selected phase-difference signal.