| 摘要 |
<p>PURPOSE:To improve the accuracy of AFC and to expand the locking range not causing mis-locking to the AFC at the same time by giving a specific frequency characteristic to the 1st and 2nd tuning circuits. CONSTITUTION:The 1st tuning circuit 1 having a center frequency fL lower than a prescribed intermediate frequency f0, the 2nd tuning circuit 3 having a center frequency fH higher than the prescribed intermediate frequency f0, the 1st detection circuit 2 detecting the output of the 1st tuning circuit 1, the 2nd detection circuit 4 detecting the output of the 2nd tuning circuit 3, and a subtraction circuit 5 generating a difference of output of the 1st and 2nd detection circuits 2, 4, are provided in the frequency discrimination circuit, and the 1st and 2nd tuning circuits 1, 3 have a frequency characteristic where the output of the subtraction circuit 5 is not zero when one of the gain or the selectivity at the center frequency of the tuning circuits 1, 3 is different and the side lobe of the input signal exists at the intermediate frequency band between the fL and fH, and the output of the subtraction circuit 5 is nearly zero when the center frequency fM of the main lobe of the input signal is nearly equal to the prescribed intermediate frequency f0.</p> |
