Electronic – Transfer Function of Inverting Ideal OP AMP with Parallel Combination T feedback network

amplifiergainoperational-amplifiertransfer functionvoltage

I've been staring at this problem for two days now and can't get the correct transfer function. I've modeled it in Simulink (Matlab) and find the magnitude of the transfer function to be ~ $$H(s) = \frac{s+20}{s+0.028}$$

I'm getting huge numbers when trying to solve it so I must be doing something wrong. I've applied KCL to solve for the currents going into the parallel combo. Can anyone offer guidance? My work is shown below.

schematic

simulate this circuit – Schematic created using CircuitLab

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Best Answer

Can anyone offer guidance?

I'm thinking the big issue you have is R3 in that it goes to ground half way along the feedback path. If so then my advice is convert Vo, R3 and R4 to a much smaller voltage source (Vx) in series with one resistor.

  • Vx will be Vo.R3/(R3+R4)
  • Series resistance will be R3||R4

It's just nortons and thevenins theorums I'm using.

Now you have a voltage source Vx in series with Rx where Rx is R2 + R3||R4.

Now go about applying the feedback in your equations but using the above.

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