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Old 31st August 2004, 08:28 PM   #1
mikeks is offline mikeks  United Kingdom
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Default LTSpice Issue...

How does one overlap traces from different simulations, and different circuits in LTSpice????

Andy_C?
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Old 1st September 2004, 06:41 PM   #2
mikeks is offline mikeks  United Kingdom
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Hello?

I need to run AC analysis on a circuit....modify values, and run AC analysis again to examine the effect of changes.....

How can i overlap both traces from these runs on the same plot in LTSpice..?
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Old 1st September 2004, 11:50 PM   #3
mikeks is offline mikeks  United Kingdom
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Andy_C, specifically, do you have a solution to this problem ?
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Old 2nd September 2004, 05:46 AM   #4
hjelm is offline hjelm  Sweden
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This is not LTSpice but maybe the functionality is the same.
I use winspice and there is a command destroy_all that deletes previous simulation results if not then you can view them by naming them in incremental order. plot AC1.v(5) AC2.v(5). Plots v(5) from AC simulations 1 and 2.
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Old 2nd September 2004, 06:38 AM   #5
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Quote:
Originally posted by mikeks
Andy_C, specifically, do you have a solution to this problem ?

Mike,

I dont now specifically LTSpice, but in most sims there is an option where you can sweep a value of a component or a source and automatically plot curves for each value. That I think is what you need. Is there anything in the help file on sweeping values or related terms?

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Old 2nd September 2004, 06:52 AM   #6
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Hi,

From what I've read.. you can't?

Perhaps you can export data to a spreadsheet and do it yourself but that's rather laborious indeed.

Might I suggest you go to sci.electronics.cad newsgroup and address your question to Mike Engelardt who codes LtSpice, if people don't tell him what they don't like about it, or of its failings, then it can't ever improve.

Let us know about any response you get please, it's a good question, it might even be enough to start a war there.

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Old 2nd September 2004, 06:33 PM   #7
mikeks is offline mikeks  United Kingdom
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Quote:
Originally posted by janneman



Mike,

I dont now specifically LTSpice, but in most sims there is an option where you can sweep a value of a component or a source and automatically plot curves for each value. That I think is what you need. Is there anything in the help file on sweeping values or related terms?

Jan Didden
Hi,

No, i don't want to return a parameter sweep......

I need to run AC analysis, disconnect a component, re-connect it to another part of the circuit...and then run another AC analysis.

The results (traces) before and after the change must appear on the same graph.....viz: overlapped.

A sim. that does not posses a simple, transparent procedure for this is just so much junk as far as i am concerned....
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Old 2nd September 2004, 07:07 PM   #8
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Quote:
Originally posted by mikeks


Hi,

No, i don't want to return a parameter sweep......

I need to run AC analysis, disconnect a component, re-connect it to another part of the circuit...and then run another AC analysis.

The results (traces) before and after the change must appear on the same graph.....viz: overlapped.

A sim. that does not posses a simple, transparent procedure for this is just so much junk as far as i am concerned....

Be creative. Put in both parts, sweep them from the nominal value to 'infinity' effectively removing them from the circuit. Do it in opposite direction for the two parts.

Jan Didden
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Old 2nd September 2004, 07:27 PM   #9
sam9 is offline sam9  United States
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I'm not sure about this but check it out. LT spice creates a .raw file when you run an analysis. Maybe this is only fro .TRAN. However, if it creates one when you run .AC then you couyld make your fisr run - rename the .eaw file then rub the second .AC and renamr that .raw file as well. Folowwing this you would have to take both files and uses them to plot the two curves in an external grapging program.

This sounds to me like a PITA and I'm not sure the .raw files that are generated are usable that way -- so this is just suggesing something to pursue.

BETTER IDEA. There is a Yahoo LT Spice users group where you might get a better answer. http://groups.yahoo.com/group/LTspice/
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Old 2nd September 2004, 08:01 PM   #10
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Quote:
Originally posted by mikeks
Hello?

I need to run AC analysis on a circuit....modify values, and run AC analysis again to examine the effect of changes.....

How can i overlap both traces from these runs on the same plot in LTSpice..?
There is a very active Yahoo Group dedicated to LTspice. It's at http://groups.yahoo.com/group/LTspice. Your particular question has been discussed there several times. All posts are archived and are searchable. Also, the files section contains much useful reference material, models, and example circuits.

You can make the values of the components you wish to vary a table function of a stepped parameter. Use the ".step" command to step the controlling parameter (e.g. .step param n list 1 2 3...) to get several runs to appear in one plot. Then edit the value field of the target components to depend on this parameter (e.g. {tbl(n,1,1k,2,1p,3,1T} ). Be sure to enclose the parametrized expression in curly braces. Use extremely large values to "disconnect" the component and extremely small values to short it out.

To display only a particular step in the plot window suffix the trace expression with the step selection operator "@n", where n is the desired step number.

Most of this information is contained in the help file and is accessible via the help search function.
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