Automatic frequency tuning circuit

摘要

A multiplier circuit multiplies a first output signal (fVCO) that has been generated by a conventional automatic phase-controlled loop circuit with a second output signal (fIF+fref) that has been generated by a phase-locked loop circuit based on a reference signal (fref). A phase difference detector circuit and an edge detector circuit receive a result of this multiplication, and carry out an edge detection (such as, for example, a pulse density corresponding to a frequency difference between a video intermediate frequency fIF and the first output signal fVCO). An automatic frequency tuning voltage is generated based on a result of this edge detection.