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Old 4th December 2011, 06:48 PM   #201
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if you want to see how LTSPICE tries to resolve the operating point when given a difficult solution, take the class AB example schematic (...\LTSpiceIV\Examples\Educational\audioamp.asc) and swap the inverting and noninverting inputs (R1 to Q2-base, R6+R7 to Q1-base) and run the sim.

i just did it.... used to be if i made such an obvious error, LTSpice would try to solve it for about 10 minutes. looks like they've improved the solvers. hmmm.... now it only takes a few seconds to latch the output to a rail.
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Last edited by unclejed613; 4th December 2011 at 06:57 PM.
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Old 5th December 2011, 09:51 PM   #202
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Originally Posted by unclejed613 View Post
. . . used to be if i made such an obvious error, LTSpice would try to solve it for about 10 minutes. looks like they've improved the solvers. hmmm . . . .
There are several options, aids, and tweaks available in the "Hacks" and "SPICE" tabs of the "Control Panel". I don't claim to understand them more than superficially, but if a circuit misbehaves during initial solution or takes excessive simulation time, playing with the options will sometimes improve the situation. The "gottcha" is remembering to restore the default options for routine use, since LTSpice retains some of those option selections on subsequent runs.

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Old 19th January 2012, 06:26 AM   #203
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Can we measure phase intermodulation distortions in a LtSpice simulation ?

If we can, how we do it ?




Last edited by gaetan8888; 19th January 2012 at 06:30 AM.
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Old 21st January 2012, 03:09 AM   #204
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I keep making the point that PIM IS IMD - you can't have more PIM than indicated by the magnitude of the IMD components

the trick is to resolve the IMD components into "quadrature" sub components, aligning and identifying one phase with "AM" IMD and the other with "FM" IMD

Cordell has his PIM rebuttal papers on his site - he outlines the design of his hardware quadrature IMD measurement

you could try siming hardware or use some ideas from my distortion residual subcircuit employing arbitrary behavioral source mathematics
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Old 24th June 2012, 10:17 PM   #205
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I'm trying to learn to use the .meas command during a .trans analysis. I want to do something simple and print the resulting attenuation in dB comparing two wave forms at their max. I tried this, to no avail:

.meas tran attenuation MAX VDB(node_after_attenuator,node_before_attenuator)

The documentation around this seems a bit sparse, has anyone done this before?
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Old 24th June 2012, 10:57 PM   #206
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You should ask the Yahoo group about it. Here is an example provided by Helmut using the .measure command to measure noise and SNR:

.step dec param x 11 10meg 10
.noise V(Vout) Vsine oct 100 10 {x}
.measure ns INTEG V(onoise)
.measure snr param -20*log10(ns)
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