ASAHI KASEI
[AK8817/18]
(9) Color Burst Signal
Burst signal is generated by a 32 bit digital frequency synthesizer.
Color Burst Frequency is selected by mode setting of NTSC / PAL.
Subcarrier Freq
Video Process 1
Standerd
(MHz)
VMOD-bit
0
NTSC-M
3.57954545
PAL-B,D,G,H,I
4.43361875
1
Burst Signal Table
(10) Sub - Carrier Reset
A function to reset sub-carrier by Color Frame sequence.
Reset function can be turned “OFF “ by setting SCR-bit of Control 1 Register.
Default value is set to enable Sub-carrier reset.
SCR
0
1
Sub-carrier phase is reset in every 2 Frames
( 4 Fields )
NTSC
Sub-carrier reset is not done
Sub-carrier phase is reset inevery 4 Frames
( 8 Fields )
PAL
Sub-carrier reset is not done
(11) Setup processing
Setup processing can be performed on Video signal by Control 2 Register Setup-bit.
Following processing is made on Luminance signal ( Y signal ) and Chroma signal ( C signal ) by the Setup processing.
Y Setup = Y x 0.925 + 7.5 IRE where Y setup is the Luminance signal after Setup processing.
C Setup = C x 0.925
(12) Video DAC
where C Setup is the Chroma signal after Setup processing.
The AK8817/18 has a 9 Bit resolution, current-drive DAC as a video DAC which runs at 29.5 / 24.5454 MHz or 27.00MHz
clock frequency.
This DAC is designed to output 1.28 V o-p at full scale under the following conditions loading resistance of 390 ohms,
VREF at 1.23 V and IREF pin resistor of 12k ohms.
[ VREF ] pin should be connected to ground via a 0.1 uF or larger capacitor.
DAC output can be turned “ON” or “OFF” by register setting and current consumption can be lowered.
When the output is turned off, it is put into high impedance condition.
Rev.001E
21
2009 / 12
AKM [ ASAHI KASEI MICROSYSTEMS ]
