Datasheet

ADV7188
Rev. A | Page 38 of 112
Chroma Gain
CAGC [1:0], Chroma Automatic Gain Control,
Address 0x2C [1:0]
These two bits select the basic mode of operation for automatic
gain control in the chroma path.
Table 45. CAGC [1:0] Function
CAGC [1:0] Description
00 Manual fixed gain (use CMG [11:0])
01 Use luma gain for chroma
10 (default) Automatic gain (based on color burst)
11 Freeze chroma gain
CAGT [1:0], Chroma Automatic Gain Timing,
Address 0x2D [7:6]
These bits allow the user to influence the tracking speed of the
chroma automatic gain control, but have an effect only if the
CAGC [1:0] bits are set to 10 (automatic gain).
Table 46. CAGT [1:0] Function
CAGT [1:0] Description
00 Slow (TC = 2 sec)
01 Medium (TC = 1 sec)
10 Fast (TC = 0.2 sec)
11 (default) Adaptive
CMG [11:0]/CG [11:0], Chroma Manual Gain/Chroma Gain,
Address 0x2D [3:0], Address 0x2E [7:0]
CMG [11:0] are dual-function bits. If these bits are 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 4 to calculate a desired gain. If
read back, these bits return the current gain value. Depending on
the setting in the CAGC [1:0] bits, this is either
• Chroma manual gain value (CAGC [1:0] set to chroma
manual gain mode)
• Chroma automatic gain value (CAGC [1:0] set to any of
the automatic modes)
Table 47. CG [11:0]/CMG [11:0] 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
()
4...0
1024
40950
_ =
≤<
=
CG
GainChroma
(4)
For example, freezing the automatic gain loop results in a
readback value of 0x47A for the CMG [11:0] bits.
1.
Convert the readback value to decimal:
0x47A = 1146d
2.
Apply Equation 4 to convert the readback value:
1146/1024 = 1.12
CKE, Color-Kill Enable, Address 0x2B [6]
This bit allows the optional color-kill function to be switched
on or off. For QAM-based video standards (PAL and NTSC)
and FM-based systems (SECAM), the threshold for the color-
kill decision is selectable via the CKILLTHR [2:0] bits
(Address 0x3D).
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.
The color-kill option only works for input signals with a modu-
lated chroma part. For component (YPrPb) input, there is no
color kill.
0—Disables color kill.
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 only to QAM-
based (NTSC and PAL) or FM-modulated (SECAM) video
standards.
To enable the color-kill function, the CKE bit must be set. For
CKILLTHR settings 000, 001, 010, and 011, chroma demodulation
inside the ADV7188 may not work satisfactorily for poor input
video signals.
Table 48. CKILLTHR [2:0] Function
Description
CKILLTHR [2:0] SECAM NTSC, PAL
000 No color kill Kill at <0.5%
001 Kill at <5% Kill at <1.5%
010 Kill at <7% Kill at <2.5%
011 Kill at <8% Kill at <4.0%
100 (default) Kill at <9.5% Kill at <8.5%
101 Kill at <15% Kill at <16.0%
110 Kill at <32% Kill at <32.0%.
111
Reserved for Analog Devices internal use only;
do not select