adv7180 Analog Devices, Inc., adv7180 Datasheet - Page 35

• Manufacturer Part Number: adv7180
• Description: 10-bit, 4 X Oversampling Sdtv Video Decoder
• Manufacturer: Analog Devices, Inc.

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