Hello
How to define the stability of an AOP that has a gain <1 Ex: a gain of 0.25
How to find the phase margin, gain <0db?
See attached document
Best regards
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Hello
How to define the stability of an AOP that has a gain <1 Ex: a gain of 0.25
How to find the phase margin, gain <0db?
See attached document
Best regards
Morning Druilhe,
This comes up enough that I tried to explain and resolve issues and methodologies in this recent article, read the comments, the site migration degraded the quality, contact me for the pdf original if interested.
Effectively the quality of the document is degraded
Can you please send me the original pdf
Thanks for your help
Well I said email me, for copyright reasons this one cannot yet be in a public post.
Hello Druilhe,
Michael is a master on operational amplifiers subjects so there is little more that I can add to his extensive treatment on the op amp inverting attenuator subject.
Here in Precision Amplifiers we usually simulate the open-loop gain/phase (Aol) response of an op amp circuit to determine its phase margin and answer the stability question. The techniques I apply are covered in the TI Precision Labs - Operational Amplifiers series. If interested, you can find the information about the series here:
https://training.ti.com/ti-precision-labs-op-amps
Using the stability analysis simulation techniques outlined I applied them to the circuit you provided in your docx file. I won't go through the details here because it would require a great deal of explanation that is covered in the TI Precision Labs information.The simulation results shown below show that your OPA827 circuit has a high phase margin of about 76-degrees so it should be unconditionally stable.
I've included my TINA Spice simulation circuit should you want to make any circuit changes.
Regards, Thomas
Precision Amplifiers Applications Engineering
Thanks Tom, trust me, there are many deep gaps in my understanding of the humble op amp even now, after 30some years.
Anyway, I did not look at the full circuit until your post - part of this is the noise gain is transitioning from the resistor set 1.4V/V to a noise gain of 1V/V by the feedback cap - both are very stable as can be seen. Without that feedback cap, this could easily get into trouble with the higher inverting input C and large R's
Hello Thomas,
Thank you for your answers, but I have one last question. See attached document.