THC7984 Datasheet, PDF (42/45 Pages) THine Electronics, Inc. – 10-bit 3-channel Video Signal Digitizer

THC7984_Rev.2.0_E
Notice about the crosstalk when using 2 ports (Port 0/ Port 1) .
Crosstalk of video signal
Although the input signal to the non-selected port will give weak noise to the signal on the selected port by crosstalk, it
has little influence as long as the signal level is normal.
If the input signal to non-selected port is abnormally higher amplitude than normal signals (nominally 1.15V peak to
peak from the bottom of the sync to the peak level of copy protection signal) and supply voltage VD is lower (1.7V) than
the typical value, the crosstalk may increase and has influence to the selected port.
The component video signal on the non-selected port should be muted (output disable) by the video switch or video
buffer prior to the device to prevent the crosstalk.
* The amplitude of component video signal (YPbPr) with sync and copy protection signal is relatively high.
Mute of non-selected port (e.g.)
RGB
(PC input)
YPbPr
(Component input)
video switch
mute
THC7984
selected port
port selection
non-selected port
Crosstalk of SOG slicer
The SOG slicer extracts a sync signal from Sync-On-Video signal (SOG, SOY). In case that the Input Sync Type of the
selected port is Sync-On-Video(2-level) (R12[1:0]=10b) and a signal is inputted to the non-selected port, there is a pos-
sibility to have an influence on the clock Jitter by crosstalk.
* When the SOG slicer is not used (including YPbPr with separated sync input) , SOG crosstalk doesn’t influence on the
clock jitter.
To prevent crosstalk of the SOG slicer, take one of following countermeasures.
1. SOG slicer of non-selected port should be Power-down
When Port 0 is selected (R12[3]=0) : SOG slicer of port 1 should be powered down (R39=FDh)
When Port 1 is selected (R12[3]=1) : SOG slicer of port 0 should be powered down (R39=FEh)
* The SOG slicer of the port which doesn’t support SOG (e.g., PC input) can be powered down and the capacitor (1nF)
of the SOG input can be eliminated.
2. The video signal on the non-selected port should be muted (output disable) by the video switch or video buffer prior to
the device to prevent the crosstalk.
By above countermeasures, the SOG activity detection of the non-selected port can’t work and the following function
can not be used.
SYNC Type Detection of non-selected port (R2C[3:2]/R2C[1:0])
Input port Automatic Selection (R12[5])
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