| Electronics > Beginners |
| Oscilloscope Bandwidth Question |
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| tggzzz:
Using 300MHz op amps for audio is a poor engineering decision: the best way to avoid oscillation is to avoid using excessively high bandwidth components. Besides, more important specs may be the slew rate into resistive load and/or the output current capability. If you are looking at "power supplies", you may need to understand where you can put a scope probe's shield. Getting that wrong could wreck the scope, the device under test, or even you. To understand more about which type of probe to use, and how to use them safely, see the references in https://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/ Switch-on transients are a good use case for requiring a storage scope. Simple transient response could be measured without a storage scope by making the transients repetitve. If you are interested in audio, a key scope specification might be the input sensitivity, and be aware of the consequences of having a scope with an 8-bit ADC in the front end. |
| magic:
This is EEVblog. Buy a 500MHz scope, hack it to 1GHz, build a rise time tester and post screenshots :popcorn: 55MHz is way above audio signal bandwidth, but you will encounter such bandwidths in opamps used for audio these days like LM4562, OPA16xx or the good old '637 because Miller compensation is brutal on them - 55MHz is what it takes to get 55k gain at 1kHz and one needs that gain for specs, particularly if driving external buffers. A 300MHz scope seems like an overkill, though. Transient response testing of supplies above a few hundred kHz will really be testing of transient response of bypass capacitors. I doubt you need to test at hundreds of MHz unless you work with RF or digital circuitry which will actually draw such ripple currents. |
| jlam:
LM4562/LME49720 and LM6172 are my personal favourites. How much bandwidth do I need to check those Opamps for Stability. Haha I knew about the Miller Compensation but never realised it was call that. :clap: Now Provided those Opamps compensated with say a 22pf capacitor in the Feedback path and 0.1uF directly on the underside of the PCB, can they still oscillate? That should have been the original question. :palm: |
| tggzzz:
--- Quote from: jlam on August 02, 2019, 08:39:49 am ---LM4562/LME49720 and LM6172 are my personal favourites. How much bandwidth do I need to check those Opamps for Stability. That should have been the original question. :palm: --- End quote --- Working out the right question is often more important and difficult than answering the question. See https://entertaininghacks.wordpress.com/library-2/good-questions-pique-our-interest-and-dont-waste-our-time-2/ for some hints :) Checking for stability is the last thing you do, and there should be no surprises. The first thing is to design for stability. |
| jlam:
Thanks to everyone. It seems like I can get by with a lot less than I thought. What would be the bare minimum I need to do this kind of work ? |
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