# Op-Amp Integrator Simulation help needed

#### mishra87

Joined Jan 17, 2016
906
Hi Guys,
please find attached LT Spice find.
I wanted to get triangular wave from 5V peak to peak (-2.5V to +2.5V) rectangular input signal with 50us high and low pulse
As per my theoretical analysis triangular wave should start from 0V to -2.5V and -2.5 to 0V , (Negative integrator).

Could anybody help me to get the results.

Regards

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#### Alec_t

Joined Sep 17, 2013
12,148
Try this :-

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#### mishra87

Joined Jan 17, 2016
906
Try this :-
Hi,

Why do you use R3, C2, R4 ?
If simple integrator circuit is as per below.

I still not understand the use of those components.

#### mishra87

Joined Jan 17, 2016
906
Try this :-

If C1 = 10n
R1 = 10K
Ton = Toff = 100us

DeltaVout = 5V

But in your simulation it is coming 2.5V only.

Thanks again

#### Alec_t

Joined Sep 17, 2013
12,148
Why do you use R3, C2, R4 ?
They provide a smoothed voltage to bias the opamp inverting input so that the output is in the 0V to -2.5V range that you want. I haven't done the maths.

#### crutschow

Joined Mar 14, 2008
27,394
Below is the simulation of your circuit, slightly modified.
I added an input DC block capacitor so that the average input is always 0Vdc, to avoid output offset from that, and lowered the value of R2 to reduce the start-up settling time.

#### Audioguru again

Joined Oct 21, 2019
3,299
I am surprised that the simulation did not use an impossible opamp with no input offset voltage.
I didn't look but maybe because the input transistor in the opamp are bipolar with some input bias current.

#### mishra87

Joined Jan 17, 2016
906
Below is the simulation of your circuit, slightly modified.
I added an input DC block capacitor so that the average input is always 0Vdc, to avoid output offset from that, and lowered the value of R2 to reduce the start-up settling time.

View attachment 205907
Hi,
I studied in some book as per below and i wanted to do the simulation but i did not see the same results in any of above simulation.
Could anyone please guide me here to get the results as per below.

Last edited:

#### Alec_t

Joined Sep 17, 2013
12,148
Try this sim. I suspect a real-world circuit won't give the same results, because of input bias tolerances and non-rail-to-rail output of the op-amp.

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#### mishra87

Joined Jan 17, 2016
906
Try this sim. I suspect a real-world circuit won't give the same results, because of input bias tolerances and non-rail-to-rail output of the op-amp.
Hi Alec_t,

Thanks for you support,
Yes, it worked as expected.

Thank you very much again !!!