operational amplifier (inverting configuration

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This is a general model for an operational amplifier in the inverting configuration (with Eplus = 0 and E1 as the input voltage). Typically the open loop gain A and the differential input resistance Rin are fixed by the choice of operational amplifier. This model requires an iterative solution; the "guess" variable can be Eout or Eminus.

In the example variable sheet shown below, a current-to-voltage converter (current follower) configuration is simulated by setting R1 to zero and specifying the input current I1. Note that the output voltage (-.99 volts) is 10% less than the "ideal" op amp value of -Rf*I1 (-1 volt) due to the current through Rin. An op amp with a higher Rin should probably be used in this application. 

Variable Sheet
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St Input     Name    Output    Unit      Comment
             Eout    -.9900892 volts     output voltage
   100000    A                           open-loop gain
   0         Eplus             volts     voltage at non-inverting input
             Eminus  .0000099  volts     voltage at inverting input
             If      .0009901  ľA        current in feedback resistance
   1000      Rf                MOhm      feedback resistance
             Iin     .0000099  ľA        input current
   1000000   Rin               Ohms      differential input resistance
             E1      .0000099  volts     input voltage #1
   .001      I1                ľA        current in R1
   0         R1                Ohms      resistance of R1


Rule Sheet
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S Rule
* Eout=A*(Eplus-Eminus)
* Eminus-Eout=If*Rf
* Iin=(Eminus-Eplus)/Rin
* E1-Eminus=I1*R1
* I1=Iin+If