Guard Ring

[dreaquil]

Hi everyone,

I was wondering if anyone would be able to help me in creating a proper guard ring in order to reduce surface leakage. I understand that I must surround the high impedance nodes with a track and connect it to one of the nodes but to completely surround them isn't possible without shorting them together... does this mean surround them and leave a small gap in order to not short them? I'm quite confused.

[owiecc]

Do not short the guard ring to the high impedance node, this way the guard ring would need guarding. You need to go all the way around the HiZ node. Maybe you will need to make the node physically smaller. Take a look at google images "guard ring pcb" to see how it is done. The guard ring has to be low impedance and its potential should be very close to the guarded node. Is should not have solder mask.

[dreaquil]

How do I route to other things if the high Z node is completely surrounded? Can I leave a small gap?

[dreaquil]

For anyone who comes across this post in the future, further to the great information provided by owieccm I also found this application note from LT which helped me out.

http://www.linear.com/solutions/1853