ADV7180
Data Sheet
Luma Gain
LG[11:0], Luma Gain, Address 0x2F[3:0], Address
0x30[7:0]
LAGC[2:0], Luma Automatic Gain Control,
Address 0x2C[6:4]
LMG[11:0], Luma Manual Gain, Address 0x2F[3:0],
Address 0x30[7:0]
The luma automatic gain control mode bits select the operating
mode for the gain control in the luma path.
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.
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 39. LAGC Function
LAGC[2:0]
Description
000
001
Manual fixed gain (use LMG[11:0])
AGC (blank level to sync tip), peak white algorithm off
•
Luma manual gain value (LAGC[2:0] set to luma manual
gain mode)
010 (default) AGC (blank level to sync tip), peak white algorithm on
•
Luma automatic gain value (LAGC[2:0] set to any of the
automatic modes)
011
100
101
110
111
Reserved
Reserved
Reserved
Reserved
Freeze gain
Table 41. LG/LMG Function
LG[11:0]/LMG[11:0] Read/Write Description
LMG[11:0] = x
LG[11:0] = x
Write
Read
Manual gain for luma path
Actual used gain
LAGT[1:0], Luma Automatic Gain Timing,
Address 0x2F[7:6]
LMG[11: 0]
LumaCalibrationFactor
Luma Gain =
(1)
The luma automatic gain timing register allows the user to
influence the tracking speed of the luminance automatic gain
control. This register only has an effect if the LAGC[2:0] register is
set to 001 or 010 (automatic gain control modes).
where LMG[11:0] is a decimal value between 1024 and 4095.
Calculation of the Luma Calibration Factor
1. Using a video source, set content to a grey field and apply
as a standard CVBS signal to the CVBS input of the board.
2. Using an oscilloscope, measure the signal at CVBS input to
ensure that its sync depth, colour burst, and luma are at the
standard levels.
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.
3. Connect the output parallel pixel bus of the ADV7180 to a
backend system that has unity gain and monitor output
voltage.
4. Measure the luma level correctly from the black level. Turn
off the Luma AGC and manually change the value of the
luma gain control register, LMG[11:0], until the output
luma level matches the input measured in Step 2.
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.
Table 40. LAGT Function
LAGT[1:0]
Description
00
01
10
Slow (TC = 2 sec)
Medium (TC = 1 sec)
Fast (TC = 0.2 sec)
Adaptive
This value, in decimal, is the luma calibration factor.
11 (default)
Rev. G | Page 36 of 120
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