Timeline for How do you calculate the noise of an op-amp circuit?
Current License: CC BY-SA 4.0
12 events
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| Oct 10, 2019 at 15:12 | history | edited | endolith | CC BY-SA 4.0 |
Add equivalent resistance image
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| Oct 10, 2019 at 15:07 | comment | added | endolith | @teeeeee Added an image to the answer | |
| Oct 10, 2019 at 15:07 | history | edited | endolith | CC BY-SA 4.0 |
Add equivalent resistance image
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| Oct 10, 2019 at 14:49 | comment | added | endolith | @teeeeee Yes, a single ohmmeter that replaces the op-amp inputs. Yes, this equivalent resistance determines the effect the input current noise of the op-amp has. Yes you remove all voltage sources and replace with shorts to ground (equivalent to making them 0 V voltage sources). I'll try to draw a picture | |
| Oct 10, 2019 at 9:21 | comment | added | teeeeee | please forgive my struggle with this, but I'm still not seeing it. Do you mean place an Ohmmeter in series with each input, with their negative sides to ground? Or a single one that would be effectively inside the op amp across the pins? Isn't the goal here to calculate the effect the input current noise of the op amp will have? Also, do you remove the voltage source and short it to gnd as well? Maybe a sketch would really help me if you have time. Can you point me to a reference where this technique of adding the Ohmmeter and gnding the output is explained? Thanks for you pateience! | |
| Oct 1, 2019 at 16:08 | comment | added | endolith | @teeeeee in other words, remove the op-amp, place a ground where its output used to be (since that's a controlled voltage source) and then connect a ohmmeter to where the input terminals used to be. Rf will be grounded like Rg is, so they are shorted together | |
| Oct 1, 2019 at 16:07 | comment | added | endolith | @teeeeee "you want to find the equivalent resistance seen from the inputs of the op-amp looking outward into the circuit, with voltage sources converted to short-circuits (to ground)." | |
| Oct 1, 2019 at 11:00 | comment | added | teeeeee | I know this is an old thread, but I am now facing something similar myself. I am confused when you calculated the equivalent resistance in your answer. You say that (m+s+p) are in parallel with (f+g)... would you be kind enough to maybe explain how to see this, or perhaps add a basic equivalent diagram? Are both Rp and Rs shorted to ground, as well as the op amp output, to be able to see this? | |
| Jan 3, 2018 at 3:56 | vote | accept | endolith | ||
| Apr 13, 2017 at 12:33 | history | edited | CommunityBot |
replaced http://electronics.stackexchange.com/ with https://electronics.stackexchange.com/
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| Jan 27, 2017 at 1:09 | history | edited | endolith | CC BY-SA 3.0 |
added 55 characters in body
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| Jan 27, 2017 at 1:02 | history | answered | endolith | CC BY-SA 3.0 |