VSP 94x2A
DATA SHEET
511
442
SRY(1V nom.)
144
16
0
upper headroom
white
CR (1.2V nom.)
511
446
SRC(0.89 V nom.)
upper headroom
100% chroma
75% chroma
burst
256
black
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
.
1.9
1.8
1.7
1.6
1.5
Conversion Range [V]
1.4
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0
8
16
24
32
40
48
56
64
CLMPST1S
CLMPD2S
CLMPST2
CLMPD2
CLMPST1S
CLMPD1S
CLMPST1
CLMPD1
Gain Control Characteristic
Fig. 2–3:
CVBS ADC Characteristic
burst
64
0
lower headroom
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.
Measurement ADC1
Clamping ADC1
Measurement ADC2
AGCADJ1, AGCADJ2 (I²C)
Measurement and Clamping RGBF
Clamping ADC2
Fig. 2–4:
Clamping Signals
8
Aug. 16, 2004; 6251-552-1DS
Micronas
MICRONAS [ MICRONAS ]
