Multilayer PCB - Shielding - Which supply on each layer?

When testing your circuit and closely inspecting something on the PCB, don't be surprised, if the voltages fluctuate with your breathing every few seconds :-). Any transparent semiconductor package can cause problems due to ambient light variations.

Paul

And somehow you can buy cheap opamps that have offsets below 1 uV + 2 nV/degC.

John

That's just it. At that frequency, not much would get trapped out. Fast fluctuations would.

I think you may need to pot the finished device, or at least conformally coat it. You could design it as a conductively cooled device, where the entire assembly is pretty much always at the same temperature.

"Paul Keinanen" wrote >

Any transparent semiconductor package can cause

Even hermetically sealed packages can be a problem. Way back when I was a test engr for a semi manufacturer I discovered that the TO-99 packages we were using leaked light up the frit seal around the legs. This wreaked havoc with Vos and Ib on OA's and IA's. Art