To improve isolation between the input and the other pins of a circuit, I used an MCP6001R SOT-23-5 op-amp which has a pin-out like this:
I am interested by the fact that there is quite some space around pin 4 to do guarding experiments.
However, when I designed the board I made a mistake: I swapped the "-" pin and the "+" pin.
I looked for an op-amp that would have the "+" pin on pin 4, but I could not find any.
As I really want to keep the signal input "isolated" on pin 4, I should either find an appropriate opamp or introduce an inversion in the feedback loop.
Fortunately, I know that I can't do this, but unfortunately I can't think of another simple solution.
The above schematic is for showing the principle of applying negative feedback on the "+" pin; it does not show the op-amp that is currently selected.
- Is there an op-amp out there that has the + input on pin4? Ideally in a SOT-23-5 package, but other suggestions are also welcome.
- Or is there a high impedance analog follower/buffer (< 1 pA input current) at a reasonable cost?
- How would I introduce a simple inversion in the feedback loop on the positive pin without breaking the stability?
It does not have to be a follower; inverting is fine too, and the amplification does not have to be 1, it can be smaller.
My input signal is a low frequency, high impedance source.