Modelling Transimpedance Amplifier

Apologies, new users cannot upload attachments - otherwise I’d upload the design.

I’m really struggling to model a specific trans-impedance amplifier.

What I’ve done.

  1. Drawn the circuit as pictured in the attached screenshot. Placed a current source.
  2. Connected it to op-amp (symbol and footprint here)
  3. Added a SPICE model from here
  4. Since the SPICE model has less pins, I’ve changed the symbol to have matching nodes to that of the SPICE model.

If I try to run with current input, I get very strange results - the input and output voltages to supply the amplifier are acting VERY strange

Can you help?

Unfortunately your circuit diagram is not very enlightening.

What is the input current looking like?
What is the value of the feedback resistor?
Where are the ±15 V power sources? For ngspice you have to add 2 spice voltage sources with +15 and -15 V.

Hopefully this is helpful! - Annoyingly I can only post one screenshot at a time.

Annotated feedback resistor - 10kOhms.

Both the power supplies are set at 15V +_ DC in Spice.

Power supply voltages are very strange…

Shows DC 15

Please have a look at KiCad Eeschema as GUI for ngspice, tutorial for setting up the simulation how to properly set up power for an OpAmp.


That limit has been removed. Welcome aboard. :smiley:

@holger - that was very helpful - I now have no ERC errors!

However, still the power supplies seem to be at strange potentials and oscillating!

Electrical engineering:
A voltage is a potential difference between two nodes.
One node is V+, the other node is … GND.
Put your voltage sources between V+ and GND and V- and GND.

Your power supply voltage sources are floating. SPICE does not model the IC power supply currents, so your circuit is actually “powered” by the input source