| 摘要 |
PURPOSE:To pull-in tuning frequencies in a wide range, by pulling in a tuning frequency which is given to an electronic tuning tuner, to an optimum tuning frequency by an AFC circuit after changing the tuning frequency to the low frequency side by counting-down if the tuning frequency is shifted from the optimum tuning frequency to the high frequency side. CONSTITUTION:When an AFC voltage is lower than a reference voltage V1 and os higher than a reference voltage V2, and the tunig frequency is higher than an optimum tuning point, a channel selecting circuit 2 sends a signal to a count- down circuit 8 to count down the value, which is set in an up/down circuit 3 by the circuit 8 by a prescribed value, and changes the tuning frequency to the low frequency side. The circuit 2 discriminates the compared result between the AFC voltage due to an AFC circuit 4 and voltages V1 and V2, and the tuning frequency is hifted to the high frequency side by counting-up when the AFC voltage is shigher than the voltage V1, and the tuning frequency is shifted to the low frequency side by counting-down in the circuit 3. Thus, the tuning frequency is approximated to the optimum tuning frequency. |
