HMP8112
internal decoding frequency of 4xf
SC
.
0
HSYNC
0
HSYNC
VIDEO INPUT
VIDEO INPUT
6.5µs
DC RESTORE
DC RESTORE
START
TIME
HAGC
HAGC
t
PW
= 2.0µs
OVERLAPPED CONTROL
START
TIME
END
TIME
END
TIME
FIGURE 2A. PLL ACQUISITION MODE
FIGURE 2B. PLL LOCKED MODE
The input sample rate converter will interpolate between
existing CLK samples to create the chroma locked (4xf
SC
)
samples needed for the color decoder. An interpolation is
done to create the 4xf
SC
pixel and a correction factor is then
applied..
INCOMING VIDEO SAMPLES
TIME
chrominance information at half line intervals throughout the
NTSC video spectrum. Therefore, NTSC has 227.5 cycles of
chrominance per NTSC line. The half of a cycle causes the
next reference burst to be 180
o
out of phase with the previ-
ous line’s burst. The two line comb efficiently removes the
chrominance information from the baseband luminance sig-
nal. When decoding NTSC, the decoder maintains full lumi-
nance bandwidth horizontally throughout the chrominance
carrier frequency range. Unlike most 2 line comb filter sepa-
ration techniques, vertical bandwidth is maintained by
means of a proprietary transform technique.
Y
I, Q
Y
RESAMPLED VIDEO
AMPLITUDE
TIME
f
H
/2
4xf
SC
f
H
/2
FIGURE 3. SAMPLE RATE CONVERSION
f
H
FREQUENCY
Y
I, Q
Y
The decoder can be used with the following video sources:
Analog Composite - NTSC M, - PAL B, D, G, H, I, N
And Special Combination PAL N
Analog S - VHS (Y/C) - NTSC M, PAL B, D, G, H, I, N
And Special Combination PAL N
AMPLITUDE
FREQUENCY
Color Separation, And Demodulation
To separate the chrominance modulated color information
from the baseband luminance signal, a 2 line comb filter is
employed. In NTSC signals the color information changes
phase 180
o
from one line to the next. This interleaves the
FIGURE 4. COMPOSITE NTSC INTERLEAVE SCHEME
For PAL systems there are 283.75 cycles of chrominance
per line. Chrominance information is spaced at quarter line
intervals with a reference phase of 135
o
. The reference
7
HARRIS [ HARRIS CORPORATION ]
