I have an instrumentation amp circuit similar to that shown in this appnote but with the first stage of the instrumentation amp made out of discrete opamps. The layout has to be done in a single layer (except for the power) with the GND plane. I am concerned with routing two Rg traces to the switch and the resistors. With the best placement I could come up with, they end up forming a relatively big loop around the amp's input pins and a few input components attached to them. I wonder whether this is a problem? Thanks.

Hi,

RG is a critical net, and should not have any current flow across it.

Any coupling to it and you will mess up your CMRR.

So long traces and large loops, are definitely a bad idea. However, you have other constraints to work with ... so another engineering trade off.

Having said that, discrete opamps are not the way forward these days ... better performance (noise) from a single Instr Amp IC, and would make your PCB layout much easier.

in any case ... good luck !