Op amp oscillator

Thread Starter

Zeeus

Joined Apr 17, 2019
598
Trying to understand circuit myself but....

Circuit is correct?
Think that second op amp has the inputs interchanged

Anyways, someone please make oscillation on spice

Thanks thanks.
 

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DarthVolta

Joined Jan 27, 2015
501
I am also learning op-amps circuits, I can just about walk through what this ones doing. I should be-able to calculate the basic info. But I'm supposed to be working on other stuff.

There's a ton of circuits I want to make now, but I'm obsessed with fixing my DMM 1st
 

MrAl

Joined Jun 17, 2014
7,761
Sorry, but your .asc file gives me a syntax error and aborts.
Does it run on your computer?
Open the .asc file in a text editor, then remove the last line.
Then open the schematic in LT Spice, then make a transient analysis command,
then reverse the power supply connections to U1, then run the analysis, then choose the output to view the waveform. It doesnt work as an oscillator yet though looks like it needs more work yet.
Oh R7 has to moved too.

Or start with this...
 

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Last edited:

MrAl

Joined Jun 17, 2014
7,761
Trying to understand circuit myself but....

Circuit is correct?
Think that second op amp has the inputs interchanged

Anyways, someone please make oscillation on spice

Thanks thanks.
To start, you have U1 power supply connections reversed.
Looks like it might need more work though.

Here's a new asc file to try and work with:
 

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Thread Starter

Zeeus

Joined Apr 17, 2019
598
To start, you have U1 power supply connections reversed.
Looks like it might need more work though.

Here's a new asc file to try and work with:
lol
Thanks

Reversing U1 made it work

Sorry for wasting your time "guys"
 

LvW

Joined Jun 13, 2013
1,078
Trying to understand circuit myself but....
Just a short remark (as it was not mentioned up to now):
Your circuit is one of the alternatives to use two integrators in a closed-loop for realizing a harmonic oscillator. Here we have the classical inverting MILLER intergrator in series with the non-inverting NIC-integrator (DEBOO integrator).
 

MrAl

Joined Jun 17, 2014
7,761
Hello,

I had to remove the very last line again and put R7 back in the right place or i would get a "floating node" error. The .asc and result files are attached below.
In the .asc file, it was only the very last line that was causing LT Spice not to open but this time the simulation command did not have to be removed. Maybe i have an older version of LT Spice. Apparently it does not like the last line being blank (crlf but no other information).
Now it runs but the frequency looks closer to 4kHz.
 

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Last edited:
This circuit appears in Thomas Frederiksen's book Intuitive IC Op Amps.

The ASC circuit has the inverting and noninverting terminals swapped on both opamps.

So it is still oscillating, but the oscillation mechanism is different from the original author.
 

MrAl

Joined Jun 17, 2014
7,761
I did think the design looked kind of over complicated, but i did not look for advantages of doing it this way either.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
598
This circuit appears in Thomas Frederiksen's book Intuitive IC Op Amps.

The ASC circuit has the inverting and noninverting terminals swapped on both opamps.

So it is still oscillating, but the oscillation mechanism is different from the original author.
I think there's an error in the book schematic

Disagree?
 
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