@lineup , loopgain plots construction is as easy as ABC. Please read what we are saying to you. Read it, do not find excuses, please.
My 12 cents:
This is an amplifier under test. Sine source is placed into feedback loop, as shown in the red rectangle. Input is shorted.
Then you plot V(out)/V(A) gain:
My 12 cents:
This is an amplifier under test. Sine source is placed into feedback loop, as shown in the red rectangle. Input is shorted.
Then you plot V(out)/V(A) gain:
Lineup, the last version of Micro-Cap still is available. It can provide loop gain, stability, phase and more plots. The files include enough examples of "famous amps of the past" which you can study, to get a much better grasp than you have now. The examples come with indications "what to run".
http://web.archive.org/web/20230214034946/http://www.spectrum-soft.com/download/download.shtm
http://web.archive.org/web/20230214034946/http://www.spectrum-soft.com/download/download.shtm
You can measure separately both the TMC loop and the global loop. I usually focus on the global loop.
By global loop, do you mean the one that includes TMC?
In other words, should the pier resistance be on the return resistance side or on the output side?
I call what I measure by connecting it to the output side as global feedback. Maybe I should have called it a major loop.
In any case, if you connect it to the feedback resistor side, you measure the loop gain that is the sum of the TMC loop and the major loop.
I am checking the stability by connecting it to the output side.
In other words, should the pier resistance be on the return resistance side or on the output side?
I call what I measure by connecting it to the output side as global feedback. Maybe I should have called it a major loop.
In any case, if you connect it to the feedback resistor side, you measure the loop gain that is the sum of the TMC loop and the major loop.
I am checking the stability by connecting it to the output side.
Hi. I tuned the amplifier as best I could, removed the input filter, and shorted the feedback using a huge capacitor. You can limit the input voltage by using an additional amplifier with tone controls connected to buses with a voltage of about 6 volts. The coil adds two zeros to the THD, but it really messes up the clip.
Attachments
I created a simple 'Open Loop Gain and Phase simulation' for dummies step-by-step presentation.
Images and individual steps (1 asc file + image(s) for each step) attached in one zip file.
Etc....
All 11 steps/slides in the zip file.
Open each asc file one by one and read comments at the bottom, and also look at corresponding image file.
You can actually run simulations in each step.
I hope I didn't miss anything.
Images and individual steps (1 asc file + image(s) for each step) attached in one zip file.
Etc....
All 11 steps/slides in the zip file.
Open each asc file one by one and read comments at the bottom, and also look at corresponding image file.
You can actually run simulations in each step.
I hope I didn't miss anything.
Here is the magnituds and the phase results of latest posted schematic.Lineup, please post it then we can discuss your results. It’s good that you are trying this
It goes from 1Hz to 1MHz
Attachments
Progress! Thats excellent!
your gain and phase plots have the right shape, but it’s the details outlined below that we have to dig into now.
Can you add the plot axis scales so we can look at actual gain and phase mag? We want to look at where the gain plot crosses the 0 dB point on the axis (unity loop gain frequency aka ULGF) and then on the phase plot we have to look at the the phase margin at the ULGF and then gain margin.
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