![](http://datasheet.mmic.net.cn/50000/9412AVK_datasheet_1931160/9412AVK_8.png)
DATA SHEET
8
Aug. 16, 2004; 6251-552-1DS
Micronas
Fig. 2–2: CVBS, Y and C Amplitude Characteristics.
When using the sync height based AGC mode, the A/D
gain increases or decreases depending on the incom-
ing signal. When using overflow detection only, the
gain is set to maximum and is reduced whenever an
’overflow’ occurs.
The signal is low pass filtered so that chrominance and
noise are not used for detection. The threshold can be
adjusted by PWTHD. A setting of ’11’ equals 511 and
means an overflow of the ADC. Other settings react for
a lower level. The gain only becomes higher when a
change of the channel is detected or is manually reset
by AGCRES. AGCFRZE holds the current AGC value.
A manual setting of the ADCs gain control is possible
using the parameters AGCADJ1 and AGCADJ2.
The conversion range (CR) is bigger than the signal
range (SRY, SRC) leaving a headroom for overshoots
.
Fig. 2–3: CVBS ADC Characteristic
2.1.3. Clamping
The timing of the clamping (pulse) control signals for
the analog inputs are derived from its corresponding
CVBS input signal. The clamping algorithm works with
a split measurement pulse and a clamping pulse. The
measurement pulse is used to detect the clamping
error. The clamping pulse is used to enable current
sources for reducing the detected clamping errors. The
start and length of the measurement signals are inde-
pendently adjustable for both channels (CLMPST1,
CLMPD1, CLMPST2, CLMPD2).
The
same
applies
for
the
clamping
signals
(CLMPST1S, CLMPD1S, CLMPST2S, CLMPD2S).
Clamping and measurement signals for RGB channel
are not separate. Clamping for these ADC are con-
trolled by CLMPST2S and CLMPD2S only. Clamping
can be suppressed for some lines by CLMPLOW and
CLMPHIGH to ignore copyprotection information. No
external sync signals are required.
Fig. 2–4: Clamping Signals
511
442
144
16
0
white
black
SR
Y(1
V
n
o
m
.)
CR
(
1.
2V
nom
.)
511
446
256
64
0
SR
C
(0.8
9V
n
o
m
.)
75
%
c
hr
om
a
100%
c
hr
oma
bur
st
bur
st
upper headroom
lower headroom
upper headroom
0
8
16
24
32
40
48
56
64
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
Gain Control Characteristic
AGCADJ1, AGCADJ2 (IC)
C
onve
rsi
on
R
ange
[V]
CLMPD2
CLMPD1S
CLMPST1S
CLMPD1
CLMPST1
Clamping ADC1
CLMPD2S
CLMPST1S
CLMPST2
Measurement ADC1
Measurement and Clamping RGBF
Clamping ADC2
Measurement ADC2