AUTOMATIC SWEEP CHANNEL SELECTION DEVICE

摘要

PURPOSE:To secure the accurate automatic tuning based on the frequency discrimination voltage. CONSTITUTION:When the automatic sweep is given to the frequency, the S-curve discrimination output of the AFC circuit is compared with reference voltage x and y at comparators 29 and 30 to generate comparison output X and Y. Voltage x is equal to the central voltage of the AFC discrimination output; while voltage y is slightly lower than the central voltage. Thus up-count CU of the tuner is stopped when signal TVXY based on comparison output Y has the rise, and down-count CD is generated. And counter 6 has the slow counting toward the central frequency after passing through the tuning frequency once. With generation of signal TVX based on comparison output X, the counting is stopped. And the value of counter 6 is written into the memory part.