Help with LTspice

----- Original Message ----- From: "viking" Newsgroups: sci.electronics.design Sent: Sunday, September 16, 2007 1:19 PM Subject: Help with LTspice

Hello Rob,

What means "steps"? What's the type of the signal? (sine?)

Three chances with .TRAN

------------------------ One simulation run: continuous frequency sweep One simulation run: stepped frequency 1Mhz, 2MHz, .. Multiple simulation runs: .step command

If you simply want the frequency response of a linear system, the .AC comamnd should be used.

Which case fits your requirement? Can you tell more what you try to simulate? It will help to give the right answer.

Best regards, Helmut

LTspice user group

text -

Hello Helmut, Sorry not giving full details. I have .tran 0.01 and an Sine source AC 1 I want to run multiple simulations (plotted on the same graph) for either a given list of frequencies or continous sweep. I've tried every combination of syntax using the .STEP comand without success (usually get syntax error). For eqample the simple set-up below:-

Version 4 SHEET 1 880 680 WIRE 128 160 128 112 WIRE 128 272 128 240 FLAG 128 272 0 FLAG 128 112 OUT SYMBOL voltage 128 144 R0 WINDOW 3 73 57 Left 0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 0.01 1000000) SYMATTR Value2 AC 1 TEXT -2 506 Left 0 !.tran 0.01

So this gives the result for 1MHz, but how to have it repeat the run for 2MHz..etc, plotted on the same graph.

Thanks Rob

"viking" schrieb im Newsbeitrag news: snipped-for-privacy@r29g2000hsg.googlegroups.com...

Hello Rob,

The curly braces {} are needed for values defined in .step commands.

I have made two sweeper examples for you.

Best regards, Helmut

Maybe the news reader breaks long TEXT-lines. Please repir it if necessary.

TEXT .... ,,,,

TEXT ....,,,,

Stepepd sweep, Test1.asc

------------------------

Version 4 SHEET 1 880 680 WIRE 128 112 128 64 WIRE 416 112 128 112 WIRE 544 112 496 112 WIRE 608 112 544 112 WIRE 544 144 544 112 WIRE 128 160 128 112 WIRE 128 272 128 240 WIRE 544 272 544 208 FLAG 128 272 0 FLAG 128 64 OUT FLAG 544 272 0 FLAG 608 112 filt IOPIN 608 112 Out SYMBOL voltage 128 144 R0 WINDOW 3 73 57 Left 0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value SINE(0 0.01 {freq1}) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 400 128 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL cap 528 144 R0 SYMATTR InstName C1 SYMATTR Value 100p TEXT 8 -72 Left 0 !.tran 100u TEXT 16 -192 Left 0 !.step param freq1 1e6 5e6 2e6 TEXT 8 -40 Left 0 !.options plotwinsize=0 TEXT 16 -160 Left 0 ;.step param freq1 list 1e6 2e6 5e6 10e6

Continuous sweep, Test2.asc

---------------------------

Version 4 SHEET 1 916 680 WIRE -208 -128 -224 -128 WIRE -224 -96 -224 -128 WIRE -224 16 -224 -16 WIRE 224 80 192 80 WIRE 224 112 224 80 WIRE 224 112 112 112 WIRE 272 112 224 112 WIRE 400 112 352 112 WIRE 464 112 400 112 WIRE -224 128 -256 128 WIRE 112 144 112 112 WIRE 400 144 400 112 WIRE 64 160 -80 160 WIRE 64 240 64 208 WIRE 112 240 112 224 WIRE 400 240 400 208 FLAG 192 80 in FLAG 400 240 0 FLAG 464 112 filt IOPIN 464 112 Out FLAG 64 240 0 FLAG 112 240 0 FLAG -224 16 0 FLAG -208 -128 vfmod FLAG -256 128 vfmod SYMBOL res 256 128 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL cap 384 144 R0 SYMATTR InstName C1 SYMATTR Value 100p SYMBOL SpecialFunctions\\\\modulate -224 128 R0 WINDOW 123 -101 123 Left 0 SYMATTR Value2 space=1 mark=10e6 SYMATTR InstName A1 SYMBOL e 112 128 R0 SYMATTR InstName E1 SYMATTR Value 0.01 SYMBOL voltage -224 -112 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value PWL(0 0.1 1m 1) TEXT 8 -72 Left 0 !.tran 1m TEXT 16 -192 Left 0 !.param fstart=1e6 fstop=5e6 TSWEEP=100u TEXT 8 -40 Left 0 !.options plotwinsize=0 TEXT 16 -160 Left 0 ;.step param freq1 list 1e6 2e6 5e6 10e6 TEXT 160 192 Left 0 ;gain

AC is NOT the same as SINE.

You can't run a .AC simultaneously with a .TRAN

...Jim Thompson

Newsbeitragnews: snipped-for-privacy@r29g2000hsg.googlegroups.com...

Hello Helmut Thanks for that. The first example is the sort of thing I'm after. But the example you give crashes the application when run! I modified it at got the following to work:-

Version 4 SHEET 1 880 680 WIRE 128 112 128 64 WIRE 416 112 128 112 WIRE 544 112 496 112 WIRE 608 112 544 112 WIRE 544 144 544 112 WIRE 128 160 128 112 WIRE 128 272 128 240 WIRE 544 272 544 208 FLAG 128 272 0 FLAG 128 64 OUT FLAG 544 272 0 FLAG 608 112 filt IOPIN 608 112 Out SYMBOL voltage 128 144 R0 WINDOW 3 73 57 Left 0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value SINE(0 0.01 {freq1} 0 0 0 100) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 400 128 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL cap 528 144 R0 SYMATTR InstName C1 SYMATTR Value 10n TEXT 224 16 Left 0 !.tran 0.01 TEXT 216 -16 Left 0 !.step param freq1 list 1000 2000 3000

But you only have to change some parameters slightly for it to fall over, for example .trans 0.1 or add some more fequencies or use 1e6 instead of 1000000.

Rob

Newsbeitragnews: snipped-for-privacy@r29g2000hsg.googlegroups.com...

Hello Helmut, thakns for that. The first example is what I'm after, but it crashes when run. I modified it to that shown below and it now runs:-

Version 4 SHEET 1 880 680 WIRE 128 112 128 64 WIRE 416 112 128 112 WIRE 544 112 496 112 WIRE 608 112 544 112 WIRE 544 144 544 112 WIRE 128 160 128 112 WIRE 128 272 128 240 WIRE 544 272 544 208 FLAG 128 272 0 FLAG 128 64 OUT FLAG 544 272 0 FLAG 608 112 filt IOPIN 608 112 Out SYMBOL voltage 128 144 R0 WINDOW 3 73 57 Left 0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value SINE(0 0.01 {freq1} 0 0 0 100) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL res 400 128 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 0 56 VBottom 0 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL cap 528 144 R0 SYMATTR InstName C1 SYMATTR Value 10n TEXT 224 16 Left 0 !.tran 0.01 TEXT 216 -16 Left 0 !.step param freq1 list 1000 2000 3000

But you only have to change a parameter slightly for it to crash, for example .tran 0.1 or add some more frequency steps.

Rob

"viking" schrieb im Newsbeitrag news: snipped-for-privacy@n39g2000hsh.googlegroups.com...

Hello Rob,

I had reported a similar problem with another circuit already to Mike this afternoon. I am sure there will be a fix latest until tomorrow. Sorry for this problem with the version 2.21m. I will reply as soon as a new version is available. If you need a previous version (e.g. 2.21f) of scad3.exe without this bug, you can download it from the Yahoo group or you send me your email address and I will mail it to you. It's 2MB in a zip-file.

Best regards, Helmut

Newsbeitragnews: snipped-for-privacy@n39g2000hsh.googlegroups.com...

Hello Helmut, Thanks for taking the time to help. I will wait for the fix to come out. I will not be able to get back to the project I was using it on untill next week. Thanks again. Rob

Hello Rob

This bug is fixed now. There is a new version of LTspice (2.21n) available for download. Please upgrade.

Btw, are you aware that this bug has been fixed on Sunday? :-)

Best regards, Helmut

Hello Helmut, Just downloaded lates version, works a treat. Thanks for taking the time to help out. Regards Rob