LT Spice generating a repetitive signal
LT Spice generating a repetitive signal
(OP)
Using LT Spice, how could I simulate a repetitive signal with 12 levels between +2V and -2V?
Intention to use it as the input for a passband filter.
Initially I tried a voltage cell with PWL output but found that it does not repeat! My fault.
Any help out there? I will appreciate that!
Intention to use it as the input for a passband filter.
Initially I tried a voltage cell with PWL output but found that it does not repeat! My fault.
Any help out there? I will appreciate that!
Agustín Tomás





RE: LT Spice generating a repetitive signal
Edit it.
Fill in the table as shown in this picture.
Have a blast.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LT Spice generating a repetitive signal
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LT Spice generating a repetitive signal
I found that even if able to repeat, PWL is not what I need.
I think is a step-like function for I want to generate a 24 steps signal following a sine-like law.
And that signal has to repeat continuously to test a filter response. See the thread about "lowpass active filter" that I started today somewhere here in this forum.
Somebody adviced to use "REPEAT" command(?) but LT Spice doesn't explain the syntax for that.
Because of my job I use to stay away from internet, sometimes for more than 24 hours. Don't worry. I will revert sooner or later.
Thanks for replying.
Agustín Tomás
RE: LT Spice generating a repetitive signal
RE: LT Spice generating a repetitive signal
0 V 0.0 Sec
0 V 0.99999 Sec
1 V 1 Sec
1 V 1.99999 Sec
2 V 2 Sec
2 V 2.99999 Sec
Will approximate a waveform stepping up by one volt every second. Unfortunately many SPICEs only allow 8 or 10 points, so you may not get 12 levels.
An uglier approach I've used for that sort of thing with no limit on the number of steps (unless there's a maximum number of circuit elements) is by putting several PULSE sources in series.
Set the voltage of each pulse to a voltage you want in the sequence. Set the Ton and Period appropriately. Use the minimum Trise and Tfall. Then tinker with the Tdelay to sequence the pulses in order so they add up to the output you want. Looks like you also have a number of pulses parameter as well, set that to some very large number if necessary. You might need to add a small RC filter to remove spikes that might remain as the step edges transition from one to another.
RE: LT Spice generating a repetitive signal
A pwl (piece wise linear) file should work for this. Place a voltage or current source on the schematic. Then put the cursor over the source and the press Ctrl right click. Now in the value field enter:
pwl file=mydata.txt
mydata.txt should be a test file of the form
time1 data1
time2 data2
timen datan
This file should be in the same folder as your circuit. pwl is only briefly mentioned in the LTspice help file.
Rick
RE: LT Spice generating a repetitive signal
TTFN
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RE: LT Spice generating a repetitive signal
After reading the manual (yes I do/did!) found that STEP is closer to what I need. And as I said already I just need to find how to employ REPEAT to get a string of steps, repeted forever.
Agustín Tomás
RE: LT Spice generating a repetitive signal
Since you haven't really described what you're trying to do, I can only guess. You need sum up a bunch of different PULSES, each pulse for its particular time slot in your waveshape, allowing to you configure the voltages independently.
TTFN
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RE: LT Spice generating a repetitive signal
Just 20 minutes calculating timing and done!
Agustín Tomás
RE: LT Spice generating a repetitive signal
I see pulse as a single voltage, not stepping, declining.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LT Spice generating a repetitive signal
Each Pulse would cover a particular time slot in the composite signal.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: LT Spice generating a repetitive signal
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: LT Spice generating a repetitive signal
If you like to see how I did it, just download the file "sine 24-steps input.asc" from here:
http:/
To be opened with LT Spice.
Please note that V1 is not PULSEd but plain DC (-1V).
Agustín Tomás
RE: LT Spice generating a repetitive signal
Well done.
Now I really see.
Thanks!
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com