| 摘要 |
In color TV receiver for SECAM-encoded signals, a single FM detector, subject to line-by-line switching of its center frequency tuning, achieves sequential demodulation of respective SECAM subcarriers. For the purpose of using an identification system of the type shown in U.S. Pat. No. 4,240,102, center frequency tuning at the R-Y subcarrier resting frequency is held throughout R-Y line interval and during lead-in burst of B-Y line interval, terminating at beginning of image portion of B-Y line interval. Transient signal component, associated with switching to B-Y subcarrier resting frequency at beginning of that image portion, is stretched into early segment of image portion by de-emphasis circuit following FM detector. To reduce adverse effects thereof on coloring of image at left edge, a differentiated version of a pulse having an appropriately directed trailing edge coinciding with transient is delivered to de-emphasis circuit output terminal, with elements of de-emphasis circuit serving as differentiator.
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