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Re: Question on loop gain and phase simulation
Hi I am encountering another problem of simulation. I just up loaded the .asc and the model files. This is a simplified version of a hybrid amplifier that has opamp as first stage and followed by two tubes. I know the gain of the two tubes together is about 50dB. The opamp gain is about 22. So the max loop gain is only about 72dB or so. But in the gain phase simulation, you can see it shows 140dB, that's way too high. I check the transient simulation to make sure there's no oscillation, the closed loop gain is correct of about 22 to 23. I played around the compensation, it makes no difference. Can you take a look whether I did something wrong? Thanks |
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Re: Question on loop gain and phase simulation
Dan, the feature ("Place .OP Data Label") was in LTspice IV too, but it doesn't go back to LTspice's beginning, so very early versions (MANY years old) did not have it.? The Changelog shows that it goes back at least as early as 2010. I THINK it was added to LTspice when it was still at LTspice III (or Switcher CAD III). Regards, Andy |
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Re: Question on loop gain and phase simulation
Hello Alan, LTspiceIV Run the simulation. ?Right mouse-click into an empty area. Choose View -> Place .op Data Label ? LTspiceXVII Right mouse-click into an empty area. Choose Draft -> Place .op Data Label If you have only a .op analysis, just clicking on? a net is sufficient to place a Data Label. Important - if you run an .AC-analysis, the DC-operating point will be only calulated, if you have a nonlinear device in the circuit. Best regards, Helmut |
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Re: Question on loop gain and phase simulation
I'll reload the VXII again soon, right now, I am just using IV to get things done first. I have a simple question, how do you display the DC voltage on a net. I just forgot, right now, I just use F6 to copy a label and put it on the new net. But I know I did it before. |
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Re: Off-topic: Help with amplifier design
Hello?John Woodgate. I do not mind creating with you the scheme you need. This topic is in my interest. It is bad to have unspent potential. I have already helped other people create amps. Therefore, write to me personally. ? Bordodynov. 03.12.2018, 21:32, "John Woodgate jmw@... [LTspice]" <ltspice@...>:
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Re: Question on loop gain and phase simulation
Alan, Is it possible that the .raw files from the two runs are colliding with one another.? I don't think its a good idea to run both programs at the same time on the exact same .asc file.? I think this will cause lots of problems because the simulation results for one run will overwrite the other.? I suspect this is your real issue and nothing related to which version of LTspice you are using. Dan ---In LTspice@..., <alan.revera@...> wrote : I open both at the same time, the same file and different answers. |
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Re: Auto loadbias and savebias for stepped simulations
Hello Vlad, I do not have the best relationship with Mike because he is still angry that I used to write about some of the inner working of LTspice (even though I did it out of admiration and not malevolence).? In the beginning he seemed tolerant (even appreciative) because I was essentially bragging about what a wonderful program he had created in ways that he wasn't allowed to.? But then one day his change of attitude was so sudden and his response so severe that I often wonder if his boss (Bob Dobkin) had just read this forum for the first time, saw what was going on and then read Mike the riot act about intellectual property protection. In the old days Mike had added several program features per my requests (for example, a cosine output on the modulate device and right clicking on a net to label it).? He still is polite and appreciative on the increasingly rare occasion when I find and report true bugs, but I often hesitate to ask for features anymore because he seems to enjoy turning down my request to the point where it may set his mind permanently against ever adding them.? Sometimes I ask Helmut or others to make such suggestions in my stead. If I were you I wouldn't hold my breath waiting for changes to .savebias and .loadbias (although who knows, because it is a good idea and it has been over ten years now since my "transgression"). ---In LTspice@..., <imbvlad@...> wrote : analogspiceman wrote: "I recently asked Mike if would be possible to add a new feature to .savebias and .loadbias invoked by the keyword ¡°eachstep¡± whereby in a stepped simulation, each succeeding step would load the bias saved by the preceding step. Among other uses, this could allow eliminating the startup transient between steps when performing a time domain frequency response analysis." What was his response? I'm also curious because, by chance, I saw this topic come up on electronics .stackexchange a few days ago. -- Vlad |
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Re: New To Spice - some questions
ericmcn wrote: ? ? "is there some gentle guide on how to get different models going for LTSPICE?" Start with LTspice's Help.? Please read it through.? It will not answer every question, and if you are completely new to circuit simulation, parts of it may even leave you more confused than before.? But it's a good start, and we all need to start somewhere and stumble a lot until we get our footing.? If you're willing to take the time, there are several more resources about SPICE -- in books, and on the Internet.? I can't recommend any one in particular.? It would take volumes to do a good job (which is probably why there isn't one resource that does it all already.) ? ? "My understanding is that there are 2 types you can use - ? ? ?1 - SUBCKT ? ? ?2 - MODELS " The short answer is, when it comes to semiconductors, that is essentially true. SPICE (not talking about LTspice here, but all SPICE programs) comes with a knowledge of many semiconductor types, and it uses .MODEL statements to describe them.? They are lists of numeric parameters. Subcircuits can describe anything, including semiconductors, where someone thought that SPICE's own models were not sufficient.? A subcircuit is just a collection of circuit elements.? Some subcircuits contain .MODELs, plus more "stuff" around them.? Some have no .MODELs, but instead use lots of "ideal" elements with formulas.? SPICE users shouldn't have to know what is inside either .MODELs or subcircuits -- but that's not always true. The answers to your questions depend on your needs.? Do you want to create models?? Or do you want to use models in simulations?? It's easier if you only need to use them and don't care what's inside them -- well, at least until something goes wrong. Andy |
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New To Spice - some questions
Hello all, I have previously used this when at Uni but really need to get more involved - is there some gentle guide on how to get different models going for LTSPICE? My understanding is that there are 2 types you can use -? 1 - SUBCKT 2 - MODELS? Is there some guides on manipulating and using the above components within LTSPICE?? I think I have the grasp of the more simple model files, is there some more examples on here.? |
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Off-topic: Help with amplifier design
¿ªÔÆÌåÓýIs anyone willing to help me by private email
with the design of an amplifier (not Class D) to drive a 300 mA
sine wave into a 170 H load (5 ohms resistance) from 40 Hz up
to 150 kHz? It needs to be a current-drive amplifier, of
course, to keep the current constant over that frequency range.
I have experience with current-drive amplifiers, but not up to
150 kHz and over 40 V output. I guess this is a project for
power FETs rather than BJTs, but that's only a guess. Input
signal can be 1 V into 10 kohms. This is an unfunded private project, but there
is a remote possibility of payback. -- Best wishes John Woodgate OOO-Own Opinions Only J M Woodgate and Associates Rayleigh, Essex UK |
John Woodgate