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Is this design good enough for low noise & cross talk?

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pavjayt

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Hello,

I have designed the board that was attached that does voltage amplifying of input signals (4 gain channels) and then conditioning 4 video signals either individually or summed into one and then inserting black level signal when the command signal is zero (coming in from another board, just a square wave signal).

It would be great if I can get some suggestions to improve the design for low noise and crosstalk. This is going to be a two layer board and I tried to keep the signal traces on the top layer as much as possible while the bottom layer is filled with ground plane.

thanks
 
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Why did you clear ground away from under the ICs?
I might put slits in the ground between amplifiers.
 
Why did you clear ground away from under the ICs?
I might put slits in the ground between amplifiers.

I designed it so that there wont be any ground noise entering into the op-amps. By slits you mean to make like a 1mm lines between the ICS with no ground plane?
 
If there is ground noise I think it will be every where. I have never seen ground being removed from under a amplifier to reduce noise.

Yes on the 1mm slits to keep ground currents in each amp from effecting the other amps.
 
If there is ground noise I think it will be every where. I have never seen ground being removed from under a amplifier to reduce noise.

Yes on the 1mm slits to keep ground currents in each amp from effecting the other amps.

Thanks for that suggestion. I updated it with 1mm slits between all op-amps. Should I keep the ground clearances under op-amps or is it unecessary? How about the ground plane under those long output traces between two sections of op-amps that are oging to d-sub conenctor, is it ok to keep it or better to clear the ground under them?
 
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I would keep the ground as solid as possible. Clearing out under a trace probably will not help.

Somewhere on the PCB needs to be "reference" or "ground". That point is "0". Everything is built on top of that. I don't like the idea of trying to keep ground away form the amplifiers. Ground needs to be clean or nothing can be clean.
 
I would keep the ground as solid as possible. Clearing out under a trace probably will not help.

Somewhere on the PCB needs to be "reference" or "ground". That point is "0". Everything is built on top of that. I don't like the idea of trying to keep ground away form the amplifiers. Ground needs to be clean or nothing can be clean.

I updated it now by removing the ground clearances under the amps. I have one more question regarding the drill holes for the board mounting, is it a good idea to conenct them to ground or leave them unconnected? Also is it better to use 470uF caps in place of 1000uF caps at the power source? I saw couple of boards using 470uF rather than 1000uF. Do I need to add more caps to clean out the source?

thanks
 

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I have one more question regarding the drill holes for the board mounting, is it a good idea to conenct them to ground or leave them unconnected?
That is a question that no two people will agree on.
1) Many people will say to only connect one point. But which point?
2) I have many times connected all points. It helps pull all the ground pints together.
3) I have done tests on points 1&2. If you ground one point you need to pick the right one. If you connect more than one point you should connect all points or all the quite points.
 
That is a question that no two people will agree on.
1) Many people will say to only connect one point. But which point?
2) I have many times connected all points. It helps pull all the ground pints together.
3) I have done tests on points 1&2. If you ground one point you need to pick the right one. If you connect more than one point you should connect all points or all the quite points.

I guess I will not connect any drill holes to ground then. Either way I am connecting the ground supply to the rack in which this board is going to be installed.

Could you please comment on the new design of ground in the updated layout?

thanks
 
Looks good to me. I think separating the amplifiers will help cross talk. The gound is very solid with the (single sided + ground) idea.
 
Very nice updated layout.

A small improvement would be to widen the + and -15V tracks. You have got enough area, and it doesn't hurt to have low impedance supply paths.
 
Very nice updated layout.

A small improvement would be to widen the + and -15V tracks. You have got enough area, and it doesn't hurt to have low impedance supply paths.

Thanks, that's exactly what I am doing right now and also adding some more capacitors at supply. Will attach the new updated layout soon.
 
I updated the design with thicker supply traces and added caps to supply. I am still concerned about the long output traces that run along the center of the board. Should I increase their width or keep them as they are (they are about 0.4mm now)?

thanks
 

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  • Gain&Video.pdf
    232.4 KB · Views: 120
I have updated the design with SMB connectors for ease of use and availability. I have also updated the ground splits for each channel in 2 different ways. Any suggestions on these new designs and which one is more preferable? I am thinking to send this design to fab house this weekend.

thanks
 

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  • Gain&Video.pdf
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  • Gain&Video2.pdf
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