Questions tagged [loop-gain]
The loop-gain tag has no usage guidance.
51
questions
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1answer
109 views
How to measure amplifier circuit loop gain
In the last few days I've tried to understand how to get the loop gain (Aol*ß) of my amplifier circuit.
I've received several suggestion.
I would like to hear your opinion on this matter.
Are these 2 ...
0
votes
1answer
95 views
Negative loop gain?
I was dimensioning the CE capacitor. To do that I was looking at some formulas seen in class. The formula (freq_C=1/(2*piReqC)) involves the knowledge of the loop gain (open loop gain*beta). It ...
0
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1answer
37 views
Calculating the loop gain for an ideal op-amp with time delay
In the circuit below, \$\tau \$ represents a time delay. We are using a first-order Pade approximation for this time delay. This means that \$\ e^{-s\tau} = (1-s\tau)/(1+s\tau)\$.
Below is the ...
0
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1answer
33 views
MATLAB model of an op-amp's Open Loop Gain
I'm using MATLAB to analyze an amplifier in a transimpedance circuit, and I'm a little lost in implementing the op amp's open-loop gain function with the following formula:
$$A(s) = A_{OL} \cdot \...
0
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1answer
83 views
Op-amp inductive output impedance oscillation
In Learning the Art of Electronics pg.362, the author presents an op-amp follower driving a long cable. I don't understand the explanation given for the cause of oscillation. In particular, the author ...
0
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2answers
75 views
Drawing the Bode Plot of a loop gain
Below I have the loop gain and the Bode plot for it, however I do not understand the phase plot. Why does it start at -90 degrees instead of 90 degrees since we have a zero? Please explain.
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0answers
31 views
Estimate the phase margin of a loop gain
The loop gain is \$10^6 /[(s+1)(1+s10^5)]\$. Below I have the Bode plot. How can I derive the unity gain frequency from the Bode Plot? How can I find the phase margin from the phase plot of the Bode?
0
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1answer
74 views
How to find voltage gain of below analog circuit without using Nodal analysis?
This is a theoretical circuit just made to see that if I can find voltage gain of circuit and it took me much calculations then anticipated to get voltage gain.I just want to find if there is better ...
0
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4answers
108 views
Negative feedback and op-amp poles
I'm trying to get a better understanding of frequency compensation for op-amps. I'll start off with a very specific questions and then get into the context. For a certain op-amp, open loop gain is ...
5
votes
2answers
193 views
What's the largest practical stable gain possible?
I have a feedback application to set the voltage of a node in which there is considerable loss in the loop. Simulations tell me that a differential voltage gain of 10000, 80dB (roughly about what you ...
0
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0answers
106 views
Estimate Phase Margin in Spice
I am trying to determine the phase margin of my design and I have come across two methods for modeling the open loop gain in spice. The problem is they are yielding slightly different results. I have ...
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0answers
54 views
Voltage regulator feedback circuit and stability analysis?
I have been analyzing following buck-regulator circuit to calculate the phase-margin and gain-margin.
Circuit Diagram:
Buck regulator with input voltage = 12 V and output voltage = 3.3 V.
Just as ...
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0answers
67 views
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2answers
394 views
Stability at loop gain <1 and 180 degree phase shift
I'm reading this article about stability of OpAmps: Link to article.
It says: "If Aβ is less than unity at the high frequencies where phase shift reaches 180°, the high-frequency phase-shifted ...
0
votes
2answers
213 views
Amount of feedback in an amplifier
Sometimes I read things like "This amplifier has 30dB of feedback", what figure is that refering to? the \$\beta\$ of the amplifier? or the loop gain \$1+A\beta \$? or the negative feedback factor \$\...
1
vote
1answer
118 views
LT spice not predicting instability
I'm trying to make a linear regulator using an op amp and a pass transistor.
Here is the circuit:
From my limited understanding you can predict the stability of the circuit's feedback loop by ...
0
votes
1answer
209 views
General Feedback Theorem - Spice model and loop gain
I am implementing the General Feedback Theorem (Prof. Middlebrook, 2006) in LTSpice, using the example given in the Spice folder.
I used it to calculate the loop gain in a simple voltage follower ...
0
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1answer
88 views
Find optimal gains transfer function
I have the following closed loop transfer function:
$$G(s) = \frac{K(s^2 + 200^2)}{0.05s^3 + (1+K)s^2 + 200{K_v}s + 200K}$$
Where \$K\$ and \$K_v\$ are gains.
My goal is to find the optimal gains ...
0
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0answers
180 views
Why gain crossover frequency must be lower than phase crossover frequency for stable systems?
As far as I understood from here, phase margin means the amount of phase that needs to be added in order to coincide with 0 db gain and -180 degrees phase. Likewise for the gain margin it means means ...
0
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0answers
62 views
Why we can consider inductor as a current source when the current loop gain infinite?
I am reading about current-mode control from this site.
Please look at the excerpt below and especially the boldfaced part.
Question:
Why we can consider inductor as a current source when the ...
1
vote
2answers
131 views
Relation between crossover freqquency of loop gain and closed loop's corner frequency when feedback is not unity
In this Control Loop Cookbook from TI, in the red box the author said that the crossover frequency (indicated in figure 2) of the open-loop is same as 3dB down frequency or corner frequency of the ...
3
votes
4answers
433 views
Differential Amplifier's Unusual Behavior
This circuit is made of one differential BJT transistor pair and voltage-amplification stage with negative feedback.
simulate this circuit – Schematic created using CircuitLab
About this ...
0
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2answers
228 views
Benefits of higher order low pass in a negative feedback loop
Let \$G(s) = \frac{Y(s)}{R(s)}\$ be the loop gain of a negative feedback loop system.
For example a system like this, where Y(s) and R(s) are the laplace
transformed functions y(t) and r(t):
...
0
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1answer
71 views
Negative Feedback Portion of Amplifier
Here, in this question, I am referring to 3 stage Lin topology amplifier (differential stage - voltage amplification stage - output power stage + negative feedback).
I am wondering about portion of ...
0
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2answers
277 views
Loop bandwith and open-, closed- loop gain in ADIsimPLL
I'm want to use ADIsimPll to calculate the loop filter properties for a PLL I want to build. I read some things in the programs help topics which I find somehow strange. Maybe you guys can help me out ...
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1answer
69 views
Any transfer function has the same denominator 1+T
Sometime ago, I came across some theory saying that in a control loop any transfer functions such as ...
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5answers
398 views
Op Amp - Specifications are given for unity gain, how to choose another gain?
TL081 datasheet gives the following specifications:
How can I find the open loop amplification?
I know that the relationship between the differential voltage amplification and the (closed or opened?) ...
-2
votes
1answer
471 views
Opamp Unity gain follower stability [closed]
Please give explanation considering opamp as ideal one as well as practical one.
Edit:
I got the explanation here. Decompensated Operational Amplifiers
0
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1answer
69 views
Open loop gain of op amp
I am not sure I am analyzing this correctly, but here's an attempt:
\$20lgA_o=92.0412dB\$, yielding \$A_o=40K\$
And
\$20lgA_o-20lg(1+100K/\omega_b)=40\$, yielding \$f_b=40.08Hz\$, hence \$f_t=f_bA_o=...
0
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1answer
3k views
calculate feedback factor in feedback circuit
Below is an exercise with solution about feedback network. I am wondering how the feedback factor is calculated like that. Could anyone shed some light on this?
0
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2answers
130 views
How do I calculate closed loop gain's deviation?
I have an exercise in my book that I am trying to solve:
How large must the magnitude of the loop gain, \$ |A \beta| \$ be in order
for the closed loop gain, \$ A_t \$, to deviate less than 0.1% ...
0
votes
1answer
285 views
Gain-Bandwidth of LTC6409
I am planning to use a differential amplifier, LTC6409 which is reported to have a GBW of 10GHz. I ran an AC analysis on LTSpice using the Spice model given here. I connected the negative input to ...
1
vote
3answers
873 views
Series-Shunt Feedback Amplifier Analysis - Finding Loop Gain
So I'm trying to solve a problem I found in a textbook (won't say which one so people can't use it to cheat on their hw) and I haven't been able to arrive at the answer found in the appendix. Please ...
1
vote
2answers
697 views
A question about loop gain, feedback and stability of an op amp circuit
I read this article on the feedback and stability concept of an op amp.
The article describes the relationship between open loop gain, closed loop gain, loop gain and some oscillation effects for the ...
0
votes
1answer
302 views
How to stabilize this op-amp/MOSFET control system
I am creating a constant-current source and am having troubles stabilizing the control loop around U3, this is the circuit:
This next picture represents the plot of loop-gain of U3:
I've tried ...
5
votes
3answers
408 views
Understanding the negative feedback and stablizing of a current limiter
Here's a current limiter circuit that uses the negative feedback to limit the current to a certain point.
simulate this circuit – Schematic created using CircuitLab
I have not studied ...
0
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2answers
164 views
Open loop gain of non-inverting amplifier
How can I find open loop gain of this non inverting amplifier. I searched for answer but couldn't find the answer. Using formula Gain=1+R2/R1
I am not able to figure out values ofR2 and R1
1
vote
2answers
503 views
Positive feedback with constant transfer functions
If I have a control loop with positive feedback, the closed loop transfer function expression is: $$\frac{Y(s)}{X(s)} = \frac{P(s)}{1-P(s)H(s)} $$
where \$P(s)\$ is the direct loop transfer function ...
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vote
2answers
121 views
Big loop gain vs. big bandwidth
If one was looking for an audio amplifier of high quality, with very low distortion, which one of these two options would be better?
Large loop gain (i.e. \$af\$) but small open loop bandwidth
Small ...
3
votes
6answers
2k views
Positive feedback and unstability
In Wikipedia's positive feedback article it is stated that given the closed loop gain $$A=\frac{a}{1-af}$$ the system is unstable if \$af>1\$.
I don't really get this. If \$a=10\$ and \$f=0.5\$ (...
-2
votes
1answer
115 views
Closed and Open Loop gain
Please Could you help me to solve this question
I foud hard time for it
These what I got
You will find the answer in Page# 1 and Page# 2
1
vote
2answers
972 views
Finding Loop Gain (Aβ) of Transimpedance Amplifier
I have been having trouble finding the loop gain (Aβ) of the following transimpedance amplifier:
simulate this circuit – Schematic created using CircuitLab
To find Aβ, the books I have looked ...
1
vote
2answers
849 views
Measuring Open Loop Gain
I have a question about open loop gain. In the circuit below, I want to measure the open loop gain of the error op-amp. I'm curious if the Current Limiting op-amp will affect my gain.
What does it ...
0
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2answers
539 views
Stability of closed-loop systems at -180 degree frequency
Say e(t) is sine wave and y(t) is sine output.
If y(t) has the same frequency as e(t) with phase shift of 180 degrees, we can only get stability of the system, if the gain of open loop at this ...
2
votes
2answers
181 views
Where is the pole introduced by the RC circuit?
I've implemented a circuit under a suggestion which solves stability issues when driving a MOSFET with an high capacitance, using an OpAmp. Now, the circuit suggested is this one, in which is modeled ...
0
votes
2answers
125 views
Linear Oscillator Frequency Problem
I was doing one of the problem sets when I stumbled upon this gem.
I know that for oscillation to occur, the gain has to be greater than 1.
The loop gain I computed is
Could anyone suggest any ...
0
votes
1answer
175 views
Closed-loop gain with source degenerated amplifier
The following circuit needs is modeled with parasitic capacitances to be analysed in frequency. I need to drive it with an MCU that can output a signal that can be some tens of kHz and I need to see ...
1
vote
1answer
464 views
Facing to real world feedback designs (here, Constant Current Generator)
I still work on a current generator made with 2 opamps and a nMOS. If I find the bias point to understand how much my LED can be driven, I still have problems to find an affordable way to derive the ...
4
votes
2answers
1k views
Loop gain(s) for multi-loop circuits
With the aim to combine some good properties of two different opamp types we can make use of the composite amplifier principle (see the figure). For example, we could combine good (small) input offset ...
0
votes
1answer
104 views
Explain me, please, what “loop response” is, to help me translate this term into other language
English in not my native language.
I've tried to find full definition of "loop response" in English, but I failed.
Here is an example of using the term "loop response":
As a working example of ...
