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Data Sheet
ADV7180
Rev. I | Page 37 of 116
Luma Gain
LAGC[2:0], Luma Automatic Gain Control,
Address 0x2C[6:4]
The luma automatic gain control mode bits select the operating
mode for the gain control in the luma path.
Table 39. LAGC Function
LAGC[2:0]
Description
000
Manual fixed gain (use LMG[11:0])
001
AGC (blank level to sync tip), peak white algorithm off
010 (default)
AGC (blank level to sync tip), peak white algorithm on
011
Reserved
100
Reserved
101
Reserved
110
Reserved
111
Freeze gain
LAGT[1:0], Luma Automatic Gain Timing,
Address 0x2F[7:6]
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).
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.
Table 40. LAGT Function
LAGT[1:0]
Description
00
Slow (TC = 2 sec)
01
Medium (TC = 1 sec)
10
Fast (TC = 0.2 sec)
11 (default)
Adaptive
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]
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.
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:
Luma manual gain value (LAGC[2:0] set to luma manual
gain mode)
Luma automatic gain value (LAGC[2:0] set to any of the
automatic modes)
Table 41. LG/LMG Function
LG[11:0]/LMG[11:0]
Read/Write
Description
LMG[11:0] = x
Write
Manual gain for luma path
LG[11:0] = x
Read
Actual used gain
r
ationFacto
LumaCalibr
LMG
Gain
Luma
0]
:
[11
=
(1)
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, color burst, and luma are at the
standard levels.
3. Connect the output parallel pixel bus of th
e 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.
This value, in decimal, is the luma calibration factor.