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