ADV7183A_15 Datasheet, PDF (33/104 Pages) Analog Devices – Multiformat SDTV Video Decoder

Luma Gain
LAGC[2:0] Luma Automatic Gain Control,
Address 0x2C [7:0]
The luma automatic gain control mode bits select the mode of
operation for the gain control in the luma path.
There are ADI internal parameters to customize the peak white
gain control. Contact ADI for more information.
Table 64. LAGC Function
LAGC[2:0] Description
000
Manual fixed gain (use LMG[11:0]).
001
AGC (blank level to sync tip).
No override through white peak.
010 (default) AGC (blank level to sync tip).
Automatic override through white peak.
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 has an effect only if the LAGC[2:0]
register is set to 001, 010, 011, or 100 (automatic gain control
modes).
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.
The update speed for the peak white algorithm can be custom-
ized by the use of internal parameters. Contact ADI for more
information.
Table 65. 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
ADV7183A
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 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, this is one
of the following values:
o Luma manual gain value (LAGC[2:0] set to luma
manual gain mode).
o Luma automatic gain value (LAGC[2:0] set to any of
the automatic modes).
Table 66. LG/LMG Function
LG[11:0]/LMG[11:0] Read/Write
LG[11:0]
Read
LMG[11:0] = X
Write
Description
Actual gain.
Manual gain for luma
path.
Luma _ Gain = ^{(0 < LG ≤ 4095)} = 0....2
(1)
2048
Example
Program the ADV7183A into manual fixed gain mode with a
desired gain of 0.89:
1. Use Equation 1 to convert the gain:
0.89 × 2048 = 1822.72
2. Truncate to integer value:
1822.72 = 1822
3. Convert to hexadecimal:
1822d = 0x71E
4. Split into two registers and program:
Luma Gain Control 1 [3:0] = 0x7
Luma Gain Control 2 [7:0] = 0x1E
5. Enable manual fixed gain mode:
Set LAGC[2:0] to 000
Rev. B | Page 33 of 104