still a newbie - another getting started with LT SPICE problem

Sep 05, 2007 4 Replies
D

Still having a problem understanding this aspect of LT Spice.



Say I draft a circuit. I must put a (voltage) source in - say sine at a constant frequency



eg SINE 0 10 150.



If I then want to see what happens to that circuit across a range of frequencies I must insert a .ac command, which allows me to specify a start and stop frequency.



eg: .ac lin 50 100 1000



when I do this I get an error saying



No AC stimulus found: Set the value of a current or voltage source to "AC 1." to make it behave as a signal generator for AC analysis.


I'm clearly not understanding dot commands (and probably lots of other things) - but I thought I *had* set an AC stimulus with the SINE "generator device" (A circle with a + - in it and the word SINE and along side it. I also thought (perhaps) the frequency arg in the sine command would be replaced by the frequence sweep in the .ac command - but it seems it completlely separate.



Please? explain what I should do to do this correctly. Thanks


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A

In the properties dialog of the voltage source, you had the SINE function radio button selected. Change this to NONE. The small signal AC analysis fields on the right-hand side will then be enabled. Enter 1 in the AC amplitude field and click OK.

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U

Andrew Holme,

Why you change SINE function to NONE option? What is the reason to kept 1 at AC amplitude field?

Thanks, Ujjappa

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M

Please be aware that it's common courtesy to reply back at the bottom so that we can easily follow what you're replying to. I moved your text around for others to read.

As for your question.. You need to disable the generation of any signal so that the AC analysis process can generate its own signal source as part of the sweep. The signal is going to start from one place and end else where, depending on how you set that part up.

The (1) in the field is just a common value. 1 is used as the base of an unspecified value, like in algebra.. etc..

Change it what ever you would like I guess.

Jamie

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