AK8811 Datasheet, PDF (16/36 Pages) Asahi Kasei Microsystems – NTSC/PAL Digital Video Encoder

ASAHI KASEI
[AK8811/12]
♦ Color burst signal
Color burst signal is generated by 24bits-length Digital Frequency Synthesizer. The Default
frequency of the color burst is selected by [Video Process 1 Register(0x01)].
Standard
NTSC-M
Sub-carrier Freq. Video Process 1
[MHz]
[VM1,VM0]
3.57954545
[0,0]
PAL-M
3.57561188
[0,1]
PAL-B,D,G,H,I
4.43361875
[1,1]
PAL-N(Arg.)
PAL-N(non-Arg.)
PAL60
NTSC-4.43
3.5820558
4.43361875
4.43361875
4.43361875
[1,0]
[1,1]
[1,1]
[1,1]
Burst Signal Table
Sub-carrier frequency 3.57561188MHz is allowed when PAL-M mode is selected.
The burst frequency and initial phase resolution are as follows.
Frequency resolution
SCH Phase resolution
0.8046Hz
360°/256
♦ Video DAC
AK8811/12 has the three current driven 10bits-DACs at 27MHz operation. The full scale
voltage of DAC is determined by the current output from IREF pin. Typical output voltage is
1.28Vo-p under the condition of VREFIN 1.235V, 12KΩ between IREF pin and Ground(AVSS)
and DAC load resistance of 390Ω. This full-scale voltage should be set in the range of 1.17V to
1.33V by adjusting the resistor which terminates IREF pin. Each DAC output can be set to
“active state” or to “inactive state” individually by [DAC Mode register(05H)]. When DAC is in
“inactive state”, the output is Hi-impedance. When all DACs are set to “inactive state”, the
analog part of AK8811/12 goes into sleep mode. In this case AK8811/12 stops outputing the
reference voltage(VREF) output. When any DAC is switched over in “active state” from sleep
mode, AK8811/12 starts outputing reference voltage. In this case AK8811/12 needs several
milisecond for VREF wake-up time.
Using internal VREF as the reference voltage, connect [VREF OUT] pin with [VREF IN] pin
and [VREF OUT] pin is terminated with more than 0.1uF capacitor.
♦ Use external Reference Voltage
In order to improve the accuracy of DAC output, external reference voltage may be used. In
this case, VREFOUT pin still needs to be terminated with more than 0.1uF capacitor.
Rev.1.1
16
2000/01