[SI-LIST] Re: Guard Rings ... DC - dielectric absorption effects

A few more questions to the group:
 
1) if I use a guard ring would it be better to route it, very close or far away 
from the ground ref that is on that layer?
          a second question ->  should it be close (say 5mil) around the 
electrode or farther?
2) should there be 1 guard ring on top and/or 1 guard ring on the bottom layer
3) I have a series resistor (1m) on the input of each electrode , is it better 
to keep the resistor closer to the electrode
or farther away?  ( the distance between the op amp and the electrode is only 
0.060") / 5 mil or 25 mil trace, obviously
no vias.
 
 
Thanks in advance !
 
 Keith Kowal

 

www.product-designs.com
 
 
 


 

> Date: Mon, 22 Nov 2010 12:26:50 -0800
> From: ci249534@xxxxxxxxx
> Subject: [SI-LIST] Re: Guard Rings ... DC - dielectric absorption effects
> To: epd2001usa@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> 
> Keith,
> I'd like to bring one more comment on top of all the rest of good ideas and 
> advices for this question: 
> 
> Depending on your specific physical design and functionality, dielectric 
> absorption may affect measurements and performance due to very long time 
> constant charge displacements inside the insulating materials, which from the 
> circuit functionality and troubleshooting perspective may look like leakage 
> currents.
> 
> Cosmin Iorga,
> NoiseCoupling.com
> http://www.noisecoupling.com
> tel: (805) 231-9786
> 
> 
> 
> 
> 
> 
> ________________________________
> From: keithK EPD <epd2001usa@xxxxxxxxxxx>
> To: si-list@xxxxxxxxxxxxx
> Sent: Thu, November 18, 2010 7:24:06 PM
> Subject: [SI-LIST] Re: Guard Rings ... DC
> 
> I am dealing with DC ! so, some of my questions are not for the entire High 
> speed audience, so I apologize 
> 
> 
> I have a 4 gig ohm electrode/electrodes(s) ..... my electrode spacing is 
> 0.230" 
> and my socket has a 0.175" diameter / 4 layer
> 
> I haven't seen much lit on the subject - 
> 
> PCB material / voids / components / etch width to the 1 resistor into the 
> opAmp 
> / given 0.060" / slots req'd 
> 
> what does conformal coating do for me....
> 
> comments, pointers to white papers, etc are welcome.
> 
> 
> Keith Kowal
> 
> www.product-designs.com
> 
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