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Protecting high impedance inputs from noise - suggestions needed !!!

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prateek_k_chd

prateek_k_chd

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Hello Everyone !!

My circuit uses a BiMos opamp in voltage follower mode. Hence very high input impedance.

The circuit looks like this:

my problem.jpg


How can I shield this from external noise ?

[If this helps then the input on the opamp is also a very high impedance one, ~giga ohms range (pH probe) ]
 

Thanks Keith

I'm already using a coax cable. The problem is that the chassis is made of plastic and hence the high impedant input picks up noise whenever a person puts their hand on it.

How do i fix that ? I guess people have faced this problem before......my guess was to use Faraday caging but I don't know how to go about it.....had someone done anything like this before ? Or some other solution ?
 

It doesn't look like coax in the photograph!

Also, you need a double sided PCB (or multilayer) with ground plane which it looks like you don't have. To get round that I would suggest you buy a reel of copper tape and put it on the top of the PCB around the amplifier area and ground it to the IC. It will look a mess but it works well if you do it properly.

Keith.
 
Alright Kieth ! will try that.
Thanks again !!
 

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