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COMB FILTER
The VB7C chassis (AVM-2780G) provides for the 2-line digital Y/C separation
IC to separate luminance (Y) and chrominance (C) signals from the composite
video signal by using 2 horizontal (H) lines separation. The Y/C separation
unit for TV set requires few external parts and no adjustment.
(1) Input Clamp
This is a sync tip clamp circuit for composite signal. This circuit makes
feedback so that the minimum data after A/D conversion and at Y/C
separation equals an internal DC bias level.
(2) A/D Converter (ADC)
This is high speed series-parallel 8 bit A/D converter. Recommended Input
level is 0.75 Vp-p (Sync chip ~ white 100%).
(3) Line Memory
This block is DRAM line memory for 1H delay.
(4) Band-Pass Filter (BFP)
This filter extracts the signal of chrominance band from composite video
signal. The center frequency is fsc.
(5) Dynamic Comb Filter (DCF)
This block is logical comb filter to extract the chrominance signal. Filtering
logic applies a correlation of two lines to reduce color dot crawl and cross
color.
(6) Color Killer Circuit (Killer)
This block is applied for black and white (B/W) signals which have no color
burst. When pin 10 (Killer) is “H,” logic stops Y/C separation and outputs
composite video signal from pin 15 (Y out).
(7) PLL (4 Times Multiply Clock Generator)
This block is a 4 times multiplier and makes 4fsc the system clock. This
block supplies the system clock (4fsc) to each block via buffers and
generates timing signals for memories.
(8) D/A Converter (DAC)
This is high speed 8 bit D/A converter. Y output level is 1.73 Vp
-
p (Typ.).
C output level is 437 mVp-p (Typ.). (Input condition is 0.75 Vp-p)
System Clock
ADC
Clamp
PLL
Color
Killer
DAC
BPF
DAC
4
10
15
13
7
+
Y Output
Color Killer
C Output
Composite
Video In
fsc
1H Line
Memory
BPF
Dynamic
Comb Filter
BPF
