Electronics > Beginners

Struggling w. a Single Supply Integrator

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eev_carl:
Hi,

I simulated 2 op amp integrator circuits from a Mims notebook.  The dual supply version works fine and I built it on my breadboard.  A square wave is converted to a triangle wave.  This is the DualSupplyIntegrator attachment.


I'm having trouble with the second circuit which is a single-supply integrator.  I'm not sure if this is an LT Spice problem in the way I set up the supply or something else I'm missing.  This version of the circuit AC couples the input, sets V- to ground, and replaces the voltage at the + terminal with V+/2.  SingleSupplyIntegrator

Thanks in advance,
Carl

ogden:

--- Quote from: eev_carl on December 12, 2018, 11:36:01 am ---I'm not sure if this is an LT Spice problem

--- End quote ---

Rest assured this is not LTSpice problem. Make both circuits as one simulation so you can compare waveforms 1:1. Beauty of simulation - you can measure voltages/waveforms in any part of the circuit. So do it - compare two circuits, go through them starting from input. Find differences and think cause of them. Maybe input capacitor is too small? If you increase input capacitor - it most likely will not have time to charge during quite short simulation time? ... and so on...

eev_carl:
Hi,

I didn't mean a problem with the software itself but how I arranged the components in LT Spice.

My question is about this specific circuit.  The following attachment is the pair of circuits from the book.

Thanks,
Carl

ogden:
First test you could make - shift not only opamp supplies but your signal source as well. Make +/- 2.5V pulse going around vref (4.5V) which is 2V to 7V and see what's coming out of the circuit. ANALYZE, do not ask me to do it for you

Also name signal lines in your 2nd circuit. How would I know where vn002 and vn004 are?

eev_carl:
Is this what you mean by making the pulse go around Vref?

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