Timeline for Analyzing an op amp circuit (transfer function) that does not match the basic cases
Current License: CC BY-SA 3.0
11 events
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| Jan 2, 2015 at 23:06 | vote | accept | mgus | ||
| Jan 2, 2015 at 12:32 | comment | added | LvW | Konstantinos, The allpass is not a phase-minimum system (it has a zero in the RHP). Therefore, you cannot derive the phase function from the magnitude response. The phase is to be calculated using the ratio Im/Re. This gives an arctan function between 180 deg and 0 deg. | |
| Jan 2, 2015 at 11:00 | comment | added | mgus | @LvW For R1=R2 and about the phase Bode plot I have an objection: as magnitude plot is a straight line at 20log(|-1|)=20log(1)=0dB from w=-oo to w=+oo, phase plot should also be a straight line at 180 degrees from w=-oo to w=+oo since the constant parameter (-1) of the t.f. is negative. Those results derive from the fact that R1=R2 which makes the pole and the residue to counteract each other. I don't understand why the phase plot should go to 0 degrees for w=+oo | |
| Jan 2, 2015 at 10:26 | comment | added | LvW | Konstantinos - answering your question: For R1=R2 the numerator is the conjugate complex form of the denominator. From this you can derive that both magnitudes are identical and the magnitude of the whole allpass function is unity. Regarding the phase, you can start with w=0, which gives an absolute value of "-1" (phase 180deg). Similarly, for w approaching infinite the absolute value is "+1" (phase 0 deg). Hence, we have a phase function from 180 deg to 0 deg (90 deg at the pole frequency 1/C*R3). | |
| Jan 2, 2015 at 9:49 | comment | added | mgus | Thanks, I got this. Now, is there any way to derive the Bode plot (magnitude and phase) from this function without knowing the values of the resistors and the capacitance? We know the residue and the pole but can we tell if R2/R1 is smaller or larger than one in order to see which comes first, the pole or the residue? | |
| Jan 2, 2015 at 0:33 | history | edited | LorenzoDonati4Ukraine-OnStrike | CC BY-SA 3.0 |
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| Jan 1, 2015 at 23:09 | comment | added | mgus | I cannot find this function after doing some algebra. Can you check the edit I posted based on your solution? What's wrong here? | |
| Jan 1, 2015 at 22:48 | history | edited | LorenzoDonati4Ukraine-OnStrike | CC BY-SA 3.0 |
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| Jan 1, 2015 at 22:37 | history | edited | LorenzoDonati4Ukraine-OnStrike | CC BY-SA 3.0 |
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| Jan 1, 2015 at 22:14 | history | edited | LorenzoDonati4Ukraine-OnStrike | CC BY-SA 3.0 |
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| Jan 1, 2015 at 22:09 | history | answered | LorenzoDonati4Ukraine-OnStrike | CC BY-SA 3.0 |