# Non inverting opamp with bias DC

I'm doing a lab work on a circuit that takes a square signal in the input and first amplify it, then shape it and the amplify it again. So the circuit is actually composed by: an amplifier (inverting), a shaper, a second amplifier (non-inverting).

The problem is in the last part, where our professors asked us to bias DC the second amplifier because our signal is between [0;0.256]V, then it is amplified to [0,1.8]V and then we want the bias to offset our signal so that it stays in [-1;+1] with a bias voltage of -0.9V. Our professor said that we should take our 5V generator (that's the only one we have left to use), use a split resistor to make it to 0.9V and then use a buffer to separate that part of the circuit from the last amplifier (so that the gain of the last amplifier depends only on the two resistors R1 and R2). When I do the simulation with LTspice without the bias part (putting to ground R1), the signal is correctly amplified to [0;1.8]V. But, when I try to insert the bias DC, the signal is shifted to [-5;-3]V (more or less) which is too much. I just want it to be shifted with a factor of 0.9 to the bottom (so that it stays between [-1;1]V).

Can you help me to understand what I am doing wrong? I'll just link the simulation, the file and photo I get

• Why use a "bunch" of power supplies? Just 2 are needed for powering all opamp's. Nov 22, 2023 at 20:52
• yeah I know, actually this is a circuit that i took from a friend of mine and they used all those power supplies and didn't get the chance to change them into one Nov 22, 2023 at 21:06