Generate a triangular waveform using Multisim/MATLAB

[Fatima Hasan]

Homework Statement

Attached below.

Relevant Equations

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Using any Electrical Engineering software:

I tried to solve this question using Multisim. Here's my attempt:

That's what I got :

Kindly,could someone tell me where is my mistake ?

 

[Jody]

Does each small subsection work? I would try breaking it up into two op-amps then see if each one works with that setup.

I don't know much about the circuit setup in that software I am noticing that on the right op-amp the way the voltage rails are connected looks different from the first one. Is that okay or allowed?

 

[Fatima Hasan]

I am noticing that on the right op-amp the way the voltage rails are connected looks different from the first one. Is that okay or allowed?

It's the same as the figure shown above.
I didn't get any error.

 

[Fatima Hasan]

I don't know much about the circuit setup in that software

I tried to simulate in MATLAB but I didn't find op-amp 741.

 

[DaveE]

Is C1 really connected to U3-6? I don't see a dot there.

 

[Fatima Hasan]

Is C1 really connected to U3-6? I don't see a dot there.

Yes, it is connected.

 

[Jody]

What's the VDD seemingly floating or is it connected to the offset? Right up against the offset pins on U3.

Earlier comment I was meaning between the left and right op-amp; not just the reference image. You assign VDD and VCC to each op-amp, but for some reason the one on the right says VCC and 15V. It's inconsistent. I suppose if the nets are equal then maybe it doesn't matter... wasn't sure.

 

[Fatima Hasan]

What's the VDD seemingly floating or is it connected to the offset? Right up against the offset pins on U3.

Earlier comment I was meaning between the left and right op-amp; not just the reference image. You assign VDD and VCC to each op-amp, but for some reason the one on the right says VCC and 15V. It's inconsistent. I suppose if the nets are equal then maybe it doesn't matter... wasn't sure.

I tried.. I didn't get the required waveform..

 

[Jody]

Can you break up the two op-amps around the center put and put an input voltage source to each one; measure the output to see if you're getting what you expect? Maybe omit R1 for now.

 

[DaveE]

Yes, it is connected.
View attachment 262069

At pin 6, the output?

 

[Fatima Hasan]

At pin 6, the output?

No, I didn't connect the capacitor to pin 6.
Sorry for misunderstanding, I didn't read your previous question well.

 

[DaveE]

No, I didn't connect the capacitor to pin 6.
Sorry for misunderstanding, I didn't read your previous question well.

It should be. Try it that way.

 

[Fatima Hasan]

It should be. Try it that way.

The result:

 

[DaveE]

Now check that every component at that node is connected. If you make all connections a "T" intersection with a dot, then you'll know. Or verify it some other way, like the netlist for example.

 

[Fatima Hasan]

Now check that every component at that node is connected. If you make all connections a "T" intersection with a dot, then you'll know. Or verify it some other way, like the netlist for example.

I checked. C1, R1, pin6 , and channel A (oscilloscope) are connected together at the same node, but the result is the same (straight line at the origin).

 

[DaveE]

Are you sure C1 should be 100pF. My rough calculation says that the ramp of the triangle (the time it takes C1 to charge) should be about 7V/usec. That is much faster than a 741 op-amp can change it's output (slew rate is about 0.1 V/usec). Also, your oscilloscope is set in the msec range. That is an odd combination for a circuit like this. Still, I'm not sure why it wouldn't oscillate at some frequency.
Try a larger value for C1, like 0.1uF maybe.

 

[Fatima Hasan]

Are you sure C1 should be 100pF. My rough calculation says that the ramp of the triangle (the time it takes C1 to charge) should be about 7V/usec. That is much faster than a 741 op-amp can change it's output (slew rate is about 0.1 V/usec). Also, your oscilloscope is set in the msec range. That is an odd combination for a circuit like this. Still, I'm not sure why it wouldn't oscillate at some frequency.
Try a larger value for C1, like 0.1uF maybe.

Got it !
After changing the value of the capacitor to 0.1uF.

Thanks for your help.