LC749870W Datasheet, PDF (31/45 Pages) Sanyo Semicon Device – Silicon gate NTSC/PAL/SECAM Digital Video Decoder

LC749870W
2. AFE and ADC
This IC (LC749870W) incorporates 1-channel of video AFE and 10-bit 30MHz ADC.
• Analog clamp (Self-clamp circuit)
The self clamp circuit clamps the sync-tip without supplying clamp pulses to AFE module. When the self-clamp
function is not used, it can be placed in power down mode using I²C_SELFCLPPWDB.
• Sync-tip clamp specifications
1.55V
1.35V
0.85V
(ADC-input reference)
0.65V
Analog input
1.0Vp
Digital output
0.35V
0.15V
1.4Vp-p range
* The figures represent the values under ideal conditions.
Clamp Setting
Self Clamp Setting
SELFCLPPWDB
1: Self Clamp enable
Main Clamp Level Setting
MAINCLPLVCNT [1:0]
00: Main Clamp Level 0.35V
ADC output code
1023
878
512
356
147
1
• Low pass filter before self-clamp
A primary LPF with a 1MHz cutoff frequency has been inserted in the stage before the self-clamp circuit as a measure
to deal with the high-frequency noise that is present in weak electric fields. The LPF function is for minimizing shifts in
the clamp levels of the self-clamp when high-frequency noise components are present in the video signals. The LPF can
be set to ON or OFF using I²C_CLPLPFON.
Input video signal (SD)
High frequency noise of
1MHz or more
Sync tip clamp
when LPF is OFF
Sync tip clamp
when LPF is ON
0.35V
0V
Clamping is performed at the lower limit
Clamping is performed at the level at which the
level of the noise components. Due to the
effect of the noise, the clamp level shifts.
noise components are removed.
It is clamped at its original position.
Fig.1 Self Clamp in Weak Electric Fields
No.A1957-31/45