To improve isolation between the input and the other pins of the circuit, I used MCP6001R SOT-23-5 Opamp which has a pinning 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 an I thought took the "-" pin as the "+" pin.
I looked for an opamp 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 the 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 OPAMP that is currently selected. Source of the schematic: Stability problem in unity-gain opAmp .
- Is there an Opamp out there that has the + input on pin4? Idealy in a SOT-23-5 package, but other suggestions are also welcome.
- Or a high impédance analog follower/buffer (<1pA 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.