ADV7180
Data Sheet
4. Turn off the Chroma AGC and manually change the
CAGT[1:0], Chroma Automatic Gain Timing,
Address 0x2D[7:6]
Chroma Gain Control Register CMG[11:0] until the
chroma level matches that measured directly from the
source.
The chroma automatic gain timing register allows the user to
influence the tracking speed of the chroma automatic gain
control. This register has an effect only if the CAGC[1:0]
register is set to 10 (automatic gain).
This value, in decimal, is the chroma calibration factor.
CKE, Color Kill Enable, Address 0x2B[6]
Table 45. CAGT Function
The color kill enable bit allows the optional color kill function
to be switched on or off.
CAGT[1:0]
Description
Slow (TC = 2 sec)
Medium (TC = 1 sec)
Reserved
00
01
10
For QAM-based video standards (PAL and NTSC) as well as
FM-based systems (SECAM), the threshold for the color kill
decision is selectable via the CKILLTHR[2:0] bits.
11 (default)
Adaptive
If color kill is enabled and the color carrier of the incoming
video signal is less than the threshold for 128 consecutive video
lines, color processing is switched off (black and white output).
To switch the color processing back on, another 128 consecutive
lines with a color burst greater than the threshold are required.
CG[11:0], Chroma Gain, Address 0x2D[3:0],
Address 0x2E[7:0]; CMG[11:0], Chroma Manual Gain,
Address 0x2D[3:0], Address 0x2E[7:0]
Chroma gain[11:0] is a dual-function register. If written to, a
desired manual chroma gain can be programmed. This gain
becomes active if the CAGC[1:0] function is switched to
manual fixed gain. See Equation 2 for calculating a desired gain.
The color kill option works only for input signals with a modulated
chroma part. For component input (YPrPb), there is no color kill.
Setting CKE to 0 disables color kill.
If read back, this register returns the current gain value.
Depending on the setting in the CAGC[1:0] bits, this is either:
Setting CKE to 1 (default) enables color kill.
CKILLTHR[2:0], Color Kill Threshold, Address 0x3D[6:4]
•
The chroma manual gain value (CAGC[1:0] set to chroma
manual gain mode).
The CKILLTHR[2:0] bits allow the user to select a threshold for
the color kill function. The threshold applies only to QAM-based
(NTSC and PAL) or FM-modulated (SECAM) video standards.
•
The chroma automatic gain value (CAGC[1:0] set to any of
the automatic modes).
To enable the color kill function, the CKE bit must be set. For
Setting 000, Setting 001, Setting 010, and Setting 011, chroma
demodulation inside the ADV7180 may not work satisfactorily
for poor input video signals.
Table 46. CG/CMG Function
CG[11:0]/CMG[11:0] Read/Write Description
CMG[11:0]
Write
Manual gain for chroma
path
CG[11:0]
Read
Currently active gain
Table 47. CKILLTHR Function
Description
CMG[11: 0]decimal
ChromaCalibrationFactor
Chroma_Gain
≅
(2)
CKILLTHR[2:0] SECAM
NTSC, PAL
Kill at <0.5%
Kill at <1.5%
Kill at <2.5%
Kill at <4%
Kill at <8.5%
Kill at <16%
Kill at <32%
000
No color kill
where ChromaCalibrationFactor is a decimal value between 0
001
010
011 (default)
100
101
Kill at <5%
Kill at <7%
Kill at <8%
Kill at <9.5%
Kill at <15%
Kill at <32%
and 4095.
Calculation of the Chroma Calibration Factor
1. Apply a CVBS signal with the color bars/SMPTE bars test
pattern content directly to the measurement equipment.
2. Ensure correct termination of 75 Ω on the measurement
equipment. Measure chroma output levels.
3. Reconnect the source to the CVBS input of the ADV7180
system that has a backend gain of 1. Repeat the
110
111
Reserved for Analog Devices internal use only;
do not select
measurement of chroma levels.
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