Patent ID: 6628345
Filing Date: 2003-09-30
Classification: H03J,H04N

Abstract:
An automatic frequency tuning (AFT) circuit comprising:an automatic phase-controlled loop circuit having a first voltage-controlled oscillator circuit which outputs a first output signal having an oscillation frequency according to a first control voltage, and a first phase detector circuit which detects phases of a video intermediate signal output from a tuner and the first output signal, wherein a signal obtained based on a result of phase detection by said first phase detector circuit is input into said first voltage-controlled oscillator circuit as the first control voltage; a phase-locked loop circuit having a second voltage controlled oscillator circuit which outputs a second output signal having an oscillation frequency according to a second control voltage, and a second phase detector circuit which detects phases of a reference signal having a frequency and the second output signal, wherein a signal obtained based on a result of phase detection by said second phase detector circuit is input into said second voltage-controlled oscillator circuit as the second control voltage; a multiplier circuit which multiplies the first output signal with the second output signal; a phase difference detector circuit which detects a phase difference between a signal obtained based on a result of multiplication by said multiplier circuit and the reference signal; an edge detector circuit which detects an edge of a signal obtained based on a result of phase detection by said phase difference detector circuit; and an AFT control voltage generator circuit that generates control voltage for feedback control of said tuner so that the frequency of the video intermediate signal has specified video intermediate frequency, based on a result of edge detection by said edge detector circuit.