RGB NTSC/PAL encoder

dogtoy

dogtoy

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Does anyone have a CXA1145 datasheet?? I can't seem to find one, and the encoder I have for my supergun seems to either be a CXA1145 or an MB3514 (why do companies dremel the manufacturer and model off of ICs???). Anyway, I was planning on adding a luma trap to this, becuase basically the component output is crap. Would a luma trap like the one on the AD725 datasheet work? I have the parts already, bc I was originally going to build my own based on an AD725. Would s-video and composite be better if I used the AD725??

http://www.analog.com/UploadedFiles/Data_Sheets/774020909AD725_0.pdf

uhhh... the schematics I drew didn't come out when posted. It's in the PDF.

Original circuit for Y trap
luma ------------------------------------1kOhm--------------> to chroma
|
ntsc/pal logic |
| |
ntsc/pal clock--|--47kOhm--|--9pF cap--|--68uH inductor
| |
1N4148 18pF
to gnd to gnd

Since I am not using the ntsc/pal switching logic of the AD725 I would not need the 18pf (to ground) and 1N4148 diode, correct? Is the 47kOhm resistor part of this circuit, and therefore not needed without the switching?

like this
luma ------------------------------------1kOhm--------------> to chroma for compos.
|
|
|
ntsc/pal clock--------------------9pF cap-----68uH inductor

Would this circuit make a usable RLC Notch filter for the luma before combination?

Thanks!!
-DogToy
 
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ttooddddyy

ttooddddyy

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I do not have the data sheet, but the pin out is here
http://www.mikeg2.freeserve.co.uk/masterful/rgb.html

Regarding the AD encoder, I think you meant the composite video was crap not the component as it doesnt have component out.
I would recommend using only the svideo output which is better than the composite with the luma trap installed. If you are using svideo only there is no need to bother with the trap components including 18pf cap, 1N4148 diode and 47K res.

For the PAL/NTSC select, the logic state is high for NTSC and low for PAL (use a 10K to the 5volts or ground respectively to hold this state on pin 1 of the device)

BTW I have used these encoders with MVS with no problems, but certain jamma boardsets do have issues. For example
http://www.neo-geo.com/forums/showthread.php?t=110832

Edit: companies scratch off the numbers to keep you guessing and prevent bootleging of their product, but its not hard to figure out the device in a case like this.
 
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dogtoy

dogtoy

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I am aware of the advantages of s-video, but sometimes my Neo and supergun go with me and s-video is not always an option.

Also, I was referring in my original post to using the trap filter described in the AD725 with a CXA1145 luma output to make watchable composite (not component...it was loud here when I was writing this). So I will not be using any logic for pal/ntsc switching. There is a switch on my encoder board for this. So I guess my question really is about which components from the AD schematic should be left off when the logic circuit is not there.
 
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ttooddddyy

ttooddddyy

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There is circuitry within the AD device involved in the luma trap, so the descrete external trap circuitry can not be simply adopted for use with the CXA, what you need is a dedicated notch filter tuned to either 3.58 or 4.43 on the luminance input (pin 18).
Do you really need to switch between PAL/NTSC ? it makes it a lot simpler if it is fixed.
 
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dogtoy

dogtoy

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I am saying that I do not need to switch between pal/ntsc, because there is a DPST switch on the board for this, so if I take the lead for the clock out of this, the circuit should work for either depending on how the switch is set. That aside, the only circuitry in the AD725 for the luma trap itself is the 1K resistor and the circuitry that combines the modified luma signal with the chroma signal right?

So what can I cut out of the luma trap circuit since I am not using the STND ntsc/pal logic on the AD725 or the 14.318.../17.734... 4FSC clock generator??
 
ttooddddyy

ttooddddyy

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dogtoy said:
the circuit should work for either depending on how the switch is set.
Click to expand...

The value of the either L or C in the trap circuit will have to be changed to tailor the response for either 4.43 or 3.58, it can not remain constant for both NTSC and PAL.
 
dogtoy

dogtoy

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Posts
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If not that, then maybe the luma trap described in the Fujitsu MB3516A pdf.

http://www.fujitsu-fme.com/datasheets/e428026.pdf

All i'm really looking for here is a luma trap circuit I can put before the luma and chroma on the board are combined. This board does not even use the composite video out pin from the encoder chip. The board is here:

http://www.converters.tv/assets/RGB to Video Converter cv04_97.pdf

All 4 of these caps are 100pF
IC2 and IC3 are quad 2 input exclusive OR gates (not sure what for other than "propagation delay") these are connected to each crystal (ntsc and pal)
IC4 is a 5V regulator

I'm about ready to just give up and deal with bad composite when I have to. Maybe i'll make that AD725 circuit sometime.
 
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