Datasheet

ADV7188
Rev. A | Page 36 of 112
Luma Gain
LAGC [2:0], Luma Automatic Gain Control,
Address 0x2C [6:4]
The luma automatic gain control mode bits select the mode of
operation for the gain control in the luma path.
Analog Devices internal parameters can be used to customize the
peak white gain control. Contact an Analog Devices representative
for more information.
Table 40. LAGC [2:0] Function
LAGC [2:0] Description
000 Manual fixed gain (use LMG [11:0])
001 Reserved
010 (default)
AGC peak white algorithm enabled
(blank level to sync tip)
011 Reserved
100
AGC peak white algorithm disabled
(blank level to sync tip)
101 Reserved
110 Reserved
111 Freeze gain
LAGT [1:0], Luma Automatic Gain Timing,
Address 0x2F [7:6]
The luma automatic gain timing bits allow the user to influence
the tracking speed of the luminance automatic gain control.
Note that these bits only have an effect if the LAGC [2:0] bits are
set to 010 or 100 (automatic gain control modes).
If peak white AGC is enabled and active (see the
Status Register 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.
The update speed for the peak white algorithm can be customized
by using internal parameters. Contact an Analog Devices
representative for more information.
Table 41. LAGT [1:0] Function
LAGT [1:0] Description
00 Slow (TC = 2 sec)
01 Medium (TC = 1 sec)
10 Fast (TC = 0.2 sec)
11 (default) Adaptive
LMG [11:0]/LG [11:0], Luma Manual Gain/Luma Gain,
Address 0x2F [3:0], Address 0x30 [7:0]
Luma manual gain [11:0] are dual-function bits. If these bits 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 2 and Equation 3 show how to
calculate a desired gain for NTSC and PAL standards,
respectively.
NTSC Luma_Gain =
63.39078.0
1128
4095]011[1024
K=
≤
<
:LMG
(2)
PAL Luma_Gain =
351.3838.0
1222
4095]011[1024
K=
≤< :LMG
(3)
If read back, this register returns the current gain value.
Depending on the settings of the LAGC [2:0] bits, this 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 42. LG [11:0]/LMG [11:0] Function
LG [11:0]/LMG [11:0] Read/Write Description
LMG [11:0] = X Write Manual gain for luma path
LG [11:0] Read Actual gain used
For example, to program the ADV7188 into manual fixed gain
mode with a desired gain of 0.89 for the NTSC standard:
1. Use Equation 2 to convert the gain:
0.95 × 1128 = 1071.6
2. Truncate to integer value:
1071.6 = 1071
3. Convert to hexadecimal:
1071d = 0x42F
4. Split into two registers and program:
Luma Gain Control 1 [3:0] = 0x4
Luma Gain Control 2 [7:0] = 0x2F
5. Enable manual fixed gain mode:
Set LAGC [2:0] to 000