---In ltspice@..., <405a82e5@...> wrote:
Thanks, Frank.
The omicron article gives good information, including derivations. Thanks for posting the link.
The first condition is pretty easy - inject the signal at the input to the op amp as shown in Lokere's demo.
I don't understand the second condition. I think it applies when you are injecting a signal across a small resistor via a transformer, where the impedances are part of the result. I don't think it was ever mentioned for applications in SPICE.
Would you care to help translate your .measure commands to the Voltage Injection method? You are familiar with the method and could avoid a lot of errors that others may encounter.
Thanks,
Mike
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I have uploaded to the Temp folder an example circuit from ?where I have included the .meas commands for the phase and gain margins. For further explanations, please see Measure_Margins.asc. I have also?reduced the step size of the .ac simulation in order to get more precise results.
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The second condition in the Omicron article means that the voltage loop gain is only a good approximation for the loop gain as long as the loop gain is much larger than the ratio |Zout/Zin|. Because the first condition means that this ratio has to be much smaller than 1, this second condition is automatically satisfied at |T|=1 (or 0 dB), where you measure the phase margin.
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Best regards,
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Frank???????????????????????????
Frank Wiedmann