AK8856VN Datasheet, PDF (20/98 Pages) Asahi Kasei Microsystems – NTSC/PAL Video Decoder

ASAHI KASEI
[AK8856VN]
PGA ( Programmable Gain Amp )
A PGA (Programmable Gain Amp) is integrated into the input stage of the AK8856.
The PGA is adjustable from 0 dB to 12 dB, with gain steps of 0.1 dB / step.
The input signal is attenuated by 50% by a resistor divider.
The PGA setting is determined by PGA Control Register (R/W) [Sub Address 0x05].
By writing a “1” to the Control 2 Register (R/W) [Sub Address 0x04] AGC-bit, the AGC function is enabled.
Since the setting of the AGC is written by the PGA Control Register (R/W) [Sub Address 0x05], the AGC
value can be read through this register (manual setting of the PGA is invalid).
When the AGC function is disabled, manual setting of the PGA gain is allowed.
Bit allocation of PGA Control Register is as follows:
[PGA Control Register]
Sub Address 0x05
bit 7
bit 6
Reserved
PGA6
0
0
bit 5
PGA5
0
bit 4
bit 3
PGA4
PGA3
Default Value
1
0
bit 2
PGA2
1
Default Value: 0x15
bit 1
bit 0
PGA1
PGA0
0
1
AGC
The AK8856 has an adaptive AGC function. When AGC is enabled, the input signal is controlled to an optimized
level by the PGA.
When AGC is turned off, manual gain setting of PGA by is allowed.
Enable / disable setting of the AGC is done by Control 2 Register (R/W) [Sub Address 0x04].
Sub Address 0x04
bit 7
bit 6
CNTSEL
NSIGDEF
0
0
bit 5
ODEV
0
bit 4
bit 3
FRMRT1
FRMRT0
Default Value
0
0
bit 2
COLKIL
0
Default Value: 0x00
bit 1
bit 0
ACC
AGC
0
0
[AGC]-bit
The [AGC] bit sets the mode of for the AGC.
[AGC]-bit
Function
Condition
0
Disable
1
Enable
note ) writing into the PGA register is possible while the AGC is enabled, but the written result is not valid to
register. The written result becomes valid to the register when the AGC is disabled.
There are two types of AGC-bits – one is AGCC-bit to set coring level, and the other is AGCTR-bit to control
transition speed between Peak AGC and Sync AGC operations.
AGCC [1:0]-bit
[AGCC]-bit setting
00
01
10
11
Function
+/- 2 LSB coring level
+/- 3 LSB coring level
+/- 4 LSB coring level
no coring
Note
MS0522-E-00
20
2006/Dec