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Yes - such a capacitor between C and E in common-B configuration provides positive feedback and, thus, increases the input impedance for rising frequencies. This can be also described by the term "invers (negative) MILLER effect". However, at the same time, the gain decreases (C parallel to Rc). Why do you expect an RHP pole? [SIZE
1 st order are inherently stable but noisy 2nd order are less noisy and C2/C1 ratio affects pole position 3rd order are inherently unstable with >180 deg phase shift and negative feedback becomes positive feedback. Rule of Thumb ratios help provide LPF additional rolloff using lag-lead filters to give phase margin at unity gain and may have
As I recall the negative feedback loop may have zeros, but the transfer function of P(s)/Q(s) for the positive input is often 1/(1+H(s)) thus the overall gain never reaches zero unless H(s) =-1
Hi guys, I have a problem about the stability of positive feedback. Let's say for a opam, it has 3 poles (LHP) at DC and 2 zeros (LHP) at wz. Then at DC, its phase shift is -270 degree , and at wz, its phase shift is -180 degree. At wz, its gain is 4. Then we connect the opam in a unity gain negative feedback structure. The phase margin of
If Real(s1) and Real (s2) is positive, the circuit will absolutely be unstable regarding to Hurwitz criteria.
Hello Analog guys I designed a current mirror OTA with a partial positive feedback, the circuit is like the one I attached from Gregorian book, Figure Nr. 3.41. After I finished the design , I have simulated the circuit with and without the positive feedback as shown in the first and second image respectively. Here I have a couple of ques
You'll determine stability by analyzing the loop gain magnitude and phase characteristic. For the simple case of monotone magnitude characteristic, a positive phase margin implies stability. A considerably larger phase margin will be required for acceptable time domain behaviour, however. Strictly speaking, an OP with only two poles and real fee
If you have a transistor with components connected from its collector circuit to its base circuit, its negative feedback, because when th collector signal goes positive, the base signal is going negative. If however you change the components so they introduce greater then 180 degrees phase shift and the transistor has a gain greater then 1. The cir
Yes, I mean the Vcc, the + pole of the battery, call it how you want! Vss is how microchip calls it in the datasheets, that's why I used it like this. I never saw the positive supply node named Vss in a datasheet. If pin 2 is the positive supply node and pin 1 more negative tahn pin 2, you'll expect a PMOS FET like Si2323.
What is the inverse laplace transform of 1/(s+a)? What do you think happens when a is positive?
Grounded load only means the the load is connected one end to a ground .. In this case the current source sources current from the positive pole to negative pole (ground) through a load .. If you use current source a current limiting resistor is not required .. See: A Constant Current Source
That's not possible! Q factor by definition is always is positive. Check for calculation error.
Thanks, flatulent. I want to realize a rising phase vs frequency, so it need a positive pole, and negative zero. But in many paper and book, there are a negative pole and positive zero.
is the other positive on the same side or opposite side? (+)AC <-- (+ OR -) AC-
It means you have peaking caused by a conjugated pole pair around 105 MHz. This pair is probably unwanted and can be caused by a feedforward path or positive feedback at that frequency. If you used feedback, is your phase margin large enough? You might be close to instability at 105MHz.
poles and zeroes introduce phase shift frequency dependant. So at some frequencies the negative feedback can turn to positive feedback
what you see are more poles at f=1e8 . Each pole adds phase shift, but phase shift larger than minus 180 degrees is subtracted from plus 180 degrees (kinda fuzzy explanation). Basically what you are seeing is that the phase shift is clipping. Also the magnitude shows a positive peek as well again, this indicates some zeros at that point. Hope
I have derived a transfer function containing 3 poles. All the coefficients are positive but from matlab analysis, there is one LHP real pole and a pair of RHP complex poles. Previously, I have a misconception that a cubic equation having all +ve coeff will yield all poles in the LHP. Could some mathematics (...)
If I am not wrong, I read that the B+ comes from the Battery positive connector/pole used in old vacuum tubes/valve operated equipment (radios).
Dear All, why a positive zeros in a transfer function creates negative phase shift (just as a pole) ? Thanks for answering.