Timeline for Stability of op-amps: "Oscillations if phase = 180° and loop gain > 1" question
Current License: CC BY-SA 4.0
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| Oct 22, 2018 at 6:23 | comment | added | Chu | If there's a phase lag of -180, the forward path is not a simple gain, but must be, at least, a 2nd order order transfer function. Hence \$\frac{A}{1+AB}\$, is not valid. | |
| Oct 21, 2018 at 17:27 | comment | added | amtravco | My question is about the statement, "If the loop gain magnitude is greater than 1 then the sinusoid will grow in amplitude. This is unstable." How does this follow from the equation Acl = A0/(1 + B*A0)? There is nothing in that equation that blows up or acts oddly for LG > 1 and phase = -180. | |
| Oct 21, 2018 at 13:24 | comment | added | LvW | You are welcome! | |
| Oct 21, 2018 at 13:18 | comment | added | Chu | @LvW Yes, I originally wrote it that way, then changed my mind. I've re-written now. Thank you. | |
| Oct 21, 2018 at 13:17 | history | edited | Chu | CC BY-SA 4.0 |
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| Oct 21, 2018 at 13:10 | comment | added | LvW | Chu.....typing error? Unity loop gain means: Magnitude of "1" and phase shift within the loop of 0 deg (360 deg). The term "loop gain" must always contain the sign at the summing junction - otherwise, misunderstanding or misinterpretations cannot be avoided (see the question under discussion). Background: Each measurement (or simulation) contains the sign at the summing junction. This can be positive or negative!! | |
| Oct 21, 2018 at 11:30 | history | edited | Chu | CC BY-SA 4.0 |
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| Oct 21, 2018 at 11:23 | history | answered | Chu | CC BY-SA 4.0 |