still a newbie - another getting started with LT SPICE probl

D

dave

Guest
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
<args> 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
 
"dave" <dave@notetnot.anetwork> wrote in message
news:48ctd3pqu85ev8gsp99r2f1fon0j0n8acj@4ax.com...
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
args> 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
Click to expand...
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.
 
On Wed, 5 Sep 2007 22:07:20 +0100, "Andrew Holme" <andrew@nospam.com>
wrote:

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.


Ah I see. Thanks.
Click to expand...
 
Andrew Holme,

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

Thanks,
Ujjappa


On Thursday, September 6, 2007 2:37:20 AM UTC+5:30, Andrew Holme wrote:
"dave" <dave@notetnot.anetwork> wrote in message
news:48ctd3pqu85ev8gsp99r2f1fon0j0n8acj@4ax.com...
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
args> 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


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.
Click to expand...
 
In article <fec7669b-be85-451d-8ec9-b93aadf1bbb6@googlegroups.com>,
ujjappa.ktrc@gmail.com says...
On Thursday, September 6, 2007 2:37:20 AM UTC+5:30, Andrew Holme wrote:
"dave" <dave@notetnot.anetwork> wrote in message
news:48ctd3pqu85ev8gsp99r2f1fon0j0n8acj@4ax.com...
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
args> 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


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.

Andrew Holme,

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

Thanks,
Ujjappa
Click to expand...
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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