AK8858 Datasheet, PDF (52/96 Pages) Asahi Kasei Microsystems – PS/SD Multi Format Video Decoder

[AK8858]
[7.27] Sync separation, sync detection, black-level detection and digital pedestal clamp
The AK8858 performs sync separation and sync detection on the digitized input signal, uses the detected sync
signal as the timing reference for the decoding process, and calculates the phase error from the separated sync
signal and applies it to control of the sampling clock.
The digitally converted input signal is clamped in the digital signal processing block. The internal clamp position
depends on the input signal type (either 286 mV sync or 300 mV sync), but pedestal position is output as code
16 (8-Bit, ITU-R BT.601) for both types. The digital pedestal clamp function can adjust the time constant and
set the coring level.
Black-level tuning can be performed in the sync separation block. The black-level fine-tuning band, which is
10 bits wide before REC 601 conversion, can be adjusted -8~+7 LSB in 1-LSB steps, with one step resulting in
a change of about 0.4 LSB in the output code
Settings for digital pedestal clamp time constant
DPCT[1:0]-bit
Transition time constant
00
Fast
01
Middle
10
Slow
11
Disable
Notes
Sub Address: 0x10 [5:4]
Digital pedestal clamp OFF
Settings for digital clamp pedestal coring level
DPCC[1:0]-bit
Transition time constant (bit)
00
±1bit
01
±2bit
10
±3bit
11
Non-coring
Sub Address: 0x10 [7:6]
Notes
Settings for black-level fine tuning
Sub Address: 0x10 [3:0]
BKLVL[3:0]-bit
Code adjustment of black level
Approx. change in 601 level (LSB)
0001
+1
+0.4LSB
0010
+2
+0.8LSB
0011
+3
+1.2LSB
0100
+4
+1.6LSB
0101
+5
+2.0LSB
0110
+6
+2.4LSB
0111
+7
+2.8LSB
0000
Default
None
1000
-8
-3.2LSB
1001
-7
-2.8LSB
1010
-6
-2.4LSB
1011
-5
-2.0LSB
1100
-4
-1.6LSB
1101
-3
-1.2LSB
1110
-2
-0.8LSB
1111
-1
-0.4LSB
The black level is adjusted upward or downward by the value of the setting, which must be in 2’s-complement
form. Black-level adjustment is also enabled during the vertical blanking interval.
MS1230-E-00
- 52 -
2010/9