Modelling Transimpedance Amplifier

Schematic Simulation (Ngspice)
1

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

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Can you help?

2

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.

3

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

Annotated feedback resistor - 10kOhms.

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4

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

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5

Power supply voltages are very strange…

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6

Shows DC 15

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7

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.

2 Likes
8

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

9

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

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

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10

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.

11

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