| 摘要 |
<p>A pull-in range expanding circuit for a TV set having digital automatic fine tuning provided by a voltage tuning system, wherein by means of resistances (R2 to R6, R9, R10) and an associated timer (R1, C1) connected in circuit with the inputs to the voltage comparator (VC), the difference between the upper and lower threshold voltages (A, B) is temporarily narrowed when a switching operation such as power on or channel selection is effected, the said threshold voltage difference returning to normal after said switching operation so that the image is not impaired during normal operation. Microprocessor (MIS) controlling varactor (VAC) also issues a pulse at switch-on or channel selection, which pulse is differentiated and triggers monostable (M). The invention enables the acquisition of offset frequencies from CATV or VTR. <IMAGE></p> |
