ADV7180
Luma Gain
LG[11:0], Luma Gain, Address 0x2F [3:0],
Address 0x30 [7:0]; LMG[11:0], Luma Manual Gain,
Address 0x2F [3:0], Address 0x30 [7:0]
LAGC[2:0], Luma Automatic Gain Control,
Address 0x2C [6:4]
Luma gain [11:0] is a dual-function register. If all of these
registers are written to, a desired manual luma gain can be
programmed. This gain becomes active if the LAGC[2:0] mode
is switched to manual fixed gain. Equation 1 shows how to
calculate a desired gain.
The luma automatic gain control mode bits select the operating
mode for the gain control in the luma path.
There are internal parameters (Analog Devices proprietary
algorithms) to customize the peak white gain control. Contact
local Analog Devices field applications engineers or local
Analog Devices distributor for more information.
If read back, this register returns the current gain value.
Depending on the setting in the LAGC[2:0] bits, the value is
one of the following:
Table 35. LAGC Function
LAGC[2:0]
Description
•
Luma manual gain value (LAGC[2:0] set to luma manual
gain mode)
000
001
Manual fixed gain (use LMG[11:0])
Reserved
•
Luma automatic gain value (LAGC[2:0] set to any of the
automatic modes)
010 (default) AGC (blank level to sync tip), peak white
algorithm on
011
100
Reserved
Table 37. LG/LMG Function
LG[11:0]/LMG[11:0] Read/Write Description
AGC (blank level to sync tip), peak white
algorithm off
LMG[11:0] = X
Write
Manual gain for luma
path
Actual used gain
101
110
111
Reserved
Reserved
Freeze gain
LG[11:0]
Read
(1024 < LMG[11:0] ≤ 4095)
LAGT[1:0], Luma Automatic Gain Timing,
Address 0x2F [7:6]
Luma Gain(525i) ≅
≅ 0.72K2.9
≅ 0.7K2.78
1410
The luma automatic gain timing register allows the user to
influence the tracking speed of the luminance automatic gain
control. Note that this register only has an effect if the
LAGC[2:0] register is set to 001, 010, 011, or 100 (automatic
gain control modes).
(1024 < LMG[11:0] ≤ 4095)
Luma Gain(NTSC) ≅
1470
(1024< LMG[11:0] ≤ 4095)
Luma Gain(PAL/625i) ≅
1535
If peak white AGC is enabled and active (see the STATUS_1[7:0],
Address 0x10 [7:0] section), the actual gain update speed is
dictated by the peak white AGC loop and, as a result, the LAGT
settings have no effect. As soon as the part leaves peak white
AGC, LAGT becomes relevant again.
≅ 0.66K2.66
(1)
For example, with a 525i input applied, program the ADV7180
into manual fixed gain mode with a desired gain of 0.89 as
follows:
The update speed for the peak white algorithm can be
customized by the use of internal parameters. Contact Analog
Devices local field engineers for more information.
1. Use Equation 1 to convert the gain:
0.89 × 1410 = 1254.9
2. Truncate to integer value:
= 1255d
Table 36. LAGT Function
LAGT[1:0]
Description
3. Convert to hexadecimal:
1255d = 0x04E7
00
01
10
Slow (TC = 2 sec)
Medium (TC = 1 sec)
Fast (TC = 0.2 sec)
Adaptive
4. Split into two registers and program:
Luma Gain Control 1 [3:0] = 0x4
Luma Gain Control 2 [7:0] = 0xE7
11 (default)
5. Enable manual fixed gain mode:
Set LAGC[2:0] to 000
Rev. A | Page 33 of 112
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