AK8855 Datasheet, PDF (20/81 Pages) Asahi Kasei Microsystems – NTSC/PAL Digital Video Decoder

[ASAHI KASEI]
AK8855
Sync-Separation, Sync-Detection
Sync-Detection and Separation are made from the digitized input signal.
The recognized Sync-signal is used as reference timing for decoding process.
Digital Pedestal Clamp
Converted input signal into digital code clamps the pedestal part.
Internal clamp levels differ depending on types of input signals ( 286mV Sync signal and 300 mV Sync signal ),
but output result operates such that pedestal position becomes at code 16 ( 8-bit Rec. 601 level ) for either case.
YC Separation
YC separation is done in a primary YC separation mode in the AK8855.
Filter characteristic used for YC separation is as follows ( shown below is a characteristic at 27 MHz sampling ).
10
0
-10 ^{0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5}
-20
-30
-40
-50
frequency[MHz]
Auto Color Control ( ACC )
This is a function to adjust Color Burst level of input signal to a proper level ( NTSC : 286 [mV] / PAL : 300
[mV] ).
Input Color signal level is decided by Color Burst signal. ACC gain is 20 dB maximum.
Sub Address 0x04
bit 7
bit 6
CNTSEL
DTFIX
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
[ ACC ]-bit
[ ACC ]-bit selects enable / disable of ACC and time constant.
[ACC]-bit
ACC Setting
0
Disable
1
Enable
Condition
ACC function operates independently from Color Saturation Adjust function ( when ACC is enabled, Color
Saturation adjustment is made on the signal which is adjusted to a proper level by ACC ).
MS0319-E-03
20
2004 / 11