AK8858 Datasheet, PDF (37/96 Pages) Asahi Kasei Microsystems – PS/SD Multi Format Video Decoder

[AK8858]
[7.17] AGC (Auto Gain Control)
The AGC function amplifies the input signal to the appropriate size and enables input to the AD converter. The
AGC function in the AK8858 is adaptive, and thus includes peak AGC as well as sync AGC.
The AGC of the AK8858 measures the size of the input signal (i.e. the difference between the sync tip and
pedestal levels), and adjusts the PGA value to bring the sync signal level to 286mV/300mV (525/625).
Peak AGC is effective for input signals in which the sync signal level is appropriate and only the active video
signal is large.
In case of component video signal and S-Video signal inputs, AGC are adjust by Y sync level.
When AGC function is enables, the setting values of AGC can be read via register Gain Control Register.
Settings for AGC time constant
AGCT[1:0]-bit
Time constant
00
Disable
01
Fast
10
Middle
11
Slow
T is the time constant.
Sub Address: 0x0A [1:0]
Notes
AGC OFF, PGA register enabled.
T= 1Field
T= 7Fields
T= 29Fields
Settings for AGC non-sensing range
AGCC[1:0]-bit
00
01
10
11
Non-sensing range
±2LSB
±3LSB
±4LSB
None
Sub Address: 0x0A [3:2]
Notes
Settings for freezing AGC function
AGCFRZ-bit
0
1
AGC status
Non-frozen
Frozen
Sub Address: 0x0A [4]
Notes
Settings for selection of quick or slow transition between peak and sync AGC
AGCTL-bit
AGC transition
0
Quick
1
Slow
Sub Address: 0x0B [0]
Notes
MS1230-E-00
- 37 -
2010/9