Kleinstein, I was hoping you would drop by... You always have the good information and suggestions. Thanks, for your help. It is much appreciated.
So those simple lever switches are OK.
Great, that's easy...
One could consider a circuit that does not need the switch at all, if the internal and external signal are just added. So the internal reference would be still used to adjust the offset and leaving the input open is enough to disable an external signal.
Good trick...
There should be no special need to use separate ground planes. It is more like one should avoid a ground plane at all, especially with the high current paths at the output.
I deleted the bottom ground plane, to lessen capacitance. It would be kind of difficult, to eliminate the top plane, because of the use of SMDs and dense populations. But, I will give it a look. I will use the bottom plane, for common feeds... power, load, etc. and separate them, with distance.
This type of circuit is more suitable to use a star ground point. A ground plane is more for higher frequency and less suitable for precision.
I had to look up "star point" ground. I have been using it, all along, but didn't know it had a name.. lol
A point too look for might be protection of the ground side of the F-gen input and the current monitoring output. These are connected to the power side and with wrong use could possibly carry high currents. So it might be a good idea to have something like a fuse or fusible resistor there.
Excellent idea... Maybe I will make their trace margins wider, too...
Another point to consider would be range switching to allow better accuracy at low currents by only using one output stage. In the current circuit it gets possibly nonlinear below about 5 mV / 0.02 Ohms = 250 mA, as the OPs can have different offsets.
I have been thinking on this one, but I could use help, with the switching design... What type of switch, where to place them, etc...
From the op amp and MOSFET suggestions that you made, on the other thread, I decided on the TVL171 and IRFP250... Does that sound good (enough)?
I will be posting, the final design... So, please watch for it. But, there is still lots to do, first.