AK8851 Datasheet, PDF (24/80 Pages) Asahi Kasei Microsystems – NTSC/PAL/SECAM Digital Video Decoder

ASAHI KASEI
[AK8851]
12. Decimation Filter
In the AK8851, the input signal is 2x over-sampled at 27 MHz, which is synchronized with the input signal, then it is
down-sampled to 13.5 MHz using a decimation filter.
The decimation filter’s frequency response plot is shown below.
Frequency [MHz]
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0
10.0
0.0
-10.0
-20.0
-30.0
-40.0
-50.0
-60.0
13.SYNC Separation/SYNC Detection/Phase-Error Detection/Black Level Fine Tuning
SYNC detection and SYNC separation are done on the digitized input signal. The recognized sync-signal is used as a
reference the timing for decoding process. The phase error signal is calculated based on the separated SYNC signal which
then controls the sampling clock.
In the SYNC separation block, the Luminance signal’s Black level can be fine-tuned.
The Fine-tuning band of the Black level is 10-bit wide (before REC 601 conversion) and up to +7 LSB addition or –8
LSB subtraction is possible, in one LSB steps. Output code changes approx. 0.4 LSB per each [1] set.
Black level adjustments are done by [Pedestal Level Control Register](R/W)[Sub Address 0x0C]. Bit allocation of
[Pedestal Level Control Register] is shown below.
Sub Address 0x0C
bit 7
bit 6
DPCC1
DPCC0
0
0
bit 5
DPCT1
0
bit 4
bit 3
DCPT0
BKLVL3
Default Value
0
0
bit 2
BKLVL2
0
Default Value : 0x00
bit 1
bit 0
BKLVL1
BKLVL0
0
0
*[BKLVL3:BKLVL0]-bit:
This register controls fine-tuning of the Black level. Preset register values are added to or subtracted from the Black level.
The preset value must be set in 2’s complement form. Black level fine-tuning is also valid during the Vertical Blanking period.
[BKLVL3:BKLVL0]-bit
Proc.
Change value in 601 level
0111
Add 7 code to black Level
about 2.8LSB is added.
0110
Add 6 code to black Level
about 2.4LSB is added.
0101
Add 5 code to black Level
about 2.0LSB is added.
0100
Add 4 code to black Level
about 1.6LSB is added.
0011
Add 3 code to black Level
about 1.2LSB is added.
0010
Add 2 code to black Level
about 0.8LSB is added.
0001
Add 1 code to black Level
about 0.4LSB is added.
0000
Default
1111
Subtract 1 code from black level
about 0.4LSB is subtracted.
1110
Subtract 2 code from black level
about 0.8LSB is subtracted.
1101
Subtract 3 code from black level
about 1.2LSB is subtracted.
1100
Subtract 4 code from black level
about 1.6LSB is subtracted.
1011
Subtract 5 code from black level
about 2.0LSB is subtracted.
1010
Subtract 6 code from black level
about 2.4LSB is subtracted.
1001
Subtract 7 code from black level
about 2.8LSB is subtracted.
1000
Subtract 8 code from black level
about 3.2LSB is subtracted.
MS0244-E-03
24
Confidential
2005 / 07