ADV7180
CAGT[1:0], Chroma Automatic Gain Timing,
Address 0x2D [7:6]
CKE, Color Kill Enable, Address 0x2B [6]
The color kill enable bit allows the optional color kill function
to be switched on or off.
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).
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.
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.
Table 41. CAGT Function
CAGT[1:0]
Description
00
01
10
Slow (TC = 2 sec)
Medium (TC = 1 sec)
Fast (TC = 0.2 sec)
Adaptive
11 (default)
The color kill option only works for input signals with a
modulated chroma part. For component input (YPrPb), there is
no color kill.
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]
Setting CKE to 0 disables color kill.
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] mode is switched to manual
fixed gain. Refer to Equation 2 for calculating a desired gain.
Setting CKE to 1 (default) enables color kill.
CKILLTHR[2:0], Color Kill Threshold, Address 0x3D
[6:4]
The CKILLTHR[2:0] bits allow the user to select a threshold for
the color kill function. The threshold applies to only QAM-
based (NTSC and PAL) or FM-modulated (SECAM) video
standards.
If read back, this register returns the current gain value.
Depending on the setting in the CAGC[1:0] bits, this is either:
•
•
The chroma manual gain value (CAGC[1:0] set to chroma
manual gain mode).
To enable the color kill function, the CKE bit must be set. For
Settings 000, 001, 010, and 011, chroma demodulation inside
the ADV7180 may not work satisfactorily for poor input video
signals.
The chroma automatic gain value (CAGC[1:0] set to any of
the automatic modes).
Table 42. CG/CMG Function
Table 43. CKILLTHR Function
CG[11:0]/CMG[11:0] Read/Write Description
Description
CMG[11:0]
Write
Manual gain for chroma
path
CKILLTHR[2:0] SECAM
NTSC, PAL
CG[11:0]
Read
Currently active gain
000
001
010
011 (default)
100
No color kill
Kill at <0.5%
Kill at <1.5%
Kill at <2.5%
Kill at <4.0%
Kill at <8.5%
Kill at <16.0%
Kill at <32.0%
Kill at <5%
Kill at <7%
Kill at <8%
Kill at <9.5%
Kill at <15%
Kill at <32%
(0 < CG ≤ 4095)
Chroma_Gain ≅
≅ 0 . . . 6.29
(2)
650
For example, freezing the automatic gain loop and reading back
the CG[11:0] register results in a value of 0x47A as follows:
101
110
1. Convert the readback value to decimal:
0x47A = 1146d
111
Reserved for Analog Devices internal use only.
Do not select.
2. Apply Equation 2 to convert the readback value:
1146/1024 = 1.12
Rev. A | Page 35 of 112
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