Opamp Stability

UPDATE 12-04-2022

Welcome to the video series, the operational amplifier, from abstraction to reality. One major pitfall, when dealing with the operational amplifier, is various circuit elements that causes oscillation. Opamp manufacturers, provide internal compensation, to alleviate most stability issues, but the issues that can cause unwanted oscillation, must be well understood.

Opamp Stability
Opamp Parasitic Capacitance
Opamp Capacitive Loads
Phase Margin

00:00 Intro
00:31 Opamp Control Model Theory and Definition of Instability
01:35 Thw Worst Things You Can Do
02:50 Dominant Pole Frequency Compensation
04:19 Internal Compensation
04:49 Phase Margin
06:48 Why Phase Margin at 0 dB?
07:35 Capacitive Load Stability Analysis
09:06 Isolation Resistor For Driving Capacitive Load
10:35 Inverting Terminal Parasitic Capacitor
12:48 Overshoot vs. Phase Margin Stability Spreadsheet

[ChrisCoulston]

Great practical design advice with well explained theory.

[feloria]

Glad I came across this channel super informative!

[nassional]

Thank you for useful informations.For the first time i was able to fully understand the phase margin.

[hardrocklobsterroll]

Always love seeing you post a video. So helpful and understandable

[mrenrollment]

Hey OldHack, good video as far as it goes but I think it would be improved by a discussion
of how the closed loop gain near and below 0db affects stability also. That and a mention of the difference that non-inverting makes near and below 0db. I mention this from recently reviewing a design with a -7db gain. Strange yes. Perhaps you discuss this in another video?

[maxpetrelli]

Thank you Sir for your excellent video. It helped me a lot in finding an oscillation problem on my new linear power supply design.

[FowlerAskew]

Wow, this is the video I wish I had when I was building up one of my first opamp circuits, a high gain narrowband filter for receiving ultrasonic signals. The filter worked well but I never fixed the terrible amplifier oscillations, and looking back I think I probably made a lot of design mistakes. Between this, the gyrator video, and all the other videos I haven't watched yet, I think I'll have retained more information about opamps from your videos than I did in college.

[shanefrank]

One of the best videos on this and much more understandable than what I have seen in textbooks. Thank you! I know that using a cap in parallel with the feedback resistor is common with inverting amplifier circuits, but I have also seen it in non-inverting amplifier circuits. Of course at higher frequencies that cap will only reduce the closed loop gain to unity, until some other pole reduces the gain further at higher frequencies. So does the cap in parallel with the feedback resistor in non-inverting configurations help with closed loop stability?

[beamfinder]

Great video as always!
But I have problems to follow the mathematics. What is the "s" in the equations, and how do I use it in practice?
Also I saw a lot of polar diagrams with poles and zeroes but I'm unable to extract any information from them. Could you make videos of these topics? This would be great!

Greetings from Germany!

[petersage]

Another great video, sir.

As I'm sure you're aware, many guitar effects pedals and guitar amps use high value feedback resistors. (I can understand it in a battery powered pedal, but in a mains powered amplifier?!) These are often used in parallel with a "treble cut" capacitor; does the capacitor help change the phase margin?

Also, what software are you using for the calculations and graphs? It looks like it would be incredibly useful for anyone working with operational amplifiers.

[RexxSchneider]

You can reduce the effect of the isolation resistor on the dc precision by using an isolation resistor _inside_ the feedback loop, but you need a larger value to regain stability, of course. The other downside is then a reduction in the ability of the opamp to drive the output close to the rails and a degradation of its ability to supply current to the next stage.