Circuit for generating horizontal synchronizing signal of display and associated method

A circuit for generating a horizontal synchronizing signal of a display, comprising:

• a first comparator, arranged to compare a luminance signal of a Component Video Connector of the display and a first reference signal to generate a compared signal;
• a control circuit, coupled to the first comparator and arranged to generate the first digital controlled signal according to the compared signal;
• a first digital-to-analog converter, coupled to the control circuit and the first comparator, arranged to generate the first reference signal to the first comparator according to the first digital controlled signal;
• a second digital-to-analog converter, coupled to the control circuit, arranged to generate a second reference signal according to a second digital controlled signal generated by the control circuit;
• and
• a second comparator, coupled to the second digital-to-analog converter, arranged to compare the luminance signal and the second reference signal to generate the horizontal synchronizing signal;
• wherein the control circuit keeps updating the first digital controlled signal to make the first reference signal substantially equal to the luminance signal, and the control circuit generates the second digital controlled signal according to the first digital controlled signal when the first reference signal substantially equals to the luminance signal.