All Questions
Tagged with negative-feedback feedback
42 questions
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Calculate feedback factor
Values and models are arbitrary. The circuit above was written on board (without values) as an exercise for "breaking the loop" method, however I do not agree with the answer which says the ...
- 21
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1
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67
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Why is the output impedance of an open-loop amplifier with a loading effect calculated by breaking the loop like this?
I'm a bit confused about how the author calculated the output impedance of the open-loop transconductance amplifier with the loading effect as follows.
(All images are taken from of the 6th edition of ...
- 270
3
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4
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320
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I need help to identify the negative feedback loop in a hysteresis comparator
Can anyone help me identify where the negative feedback path is?
I want to determine the feedback factors for both negative and positive feedback, but it's not clear to me where the negative feedback ...
- 270
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1
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88
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About stability in system with loop gain AB>1 in negative feedback
I have been reading about stability and feedback systems, and a very silly issue has appeared.
We can describe a negative feedback system as what can be seen in the following picture:
Image source: ...
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2
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190
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How to analyse this with nullor block?
The first is the schematics from NMOS4 with parasitic capacitance:
I recently read an article on how to analyse the circuit with The Nullor and Some Applications.
The equivalent nullor circuit. I am ...
- 849
3
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1
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174
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How to break the feedback loop and add the loading?
I am trying to break the feedback loop of a fully differential amplifier and add the loading to the input and output:
I want to do this to take into account the loading of the feedback network on the ...
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0
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48
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How to determine if the feedback is positive or negative?
How to know if I have to apply the formula Af=A/(1-AB) [positive feedback] or Af=A/(1+AB) [negative feedback]?
3
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1
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145
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I don't understand this temperature controller circuit's behaviour [duplicate]
I am trying to build a circuit to regulate temperature for a few microheaters. Here's the circuit I am using:
This is a constant temperature controller circuit often found in the research papers and ...
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2
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2
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230
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Contradiction between two circuit simulators in measuring open loop gain
I am implementing what I've learned over the past couple of days. This relates mainly to the simulation of a voltage regulator.
I built the (roughly) same circuit in both TINA TI and LTspice to ...
- 491
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3
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1k
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Why are these voltage regulators seemingly using positive feedback?
Looking over LDO / voltage regulator topologies I keep seeing examples of LDOs where the feedback network is connected to the non-inverting input terminal of the error amplifier.
Like this:
Taken ...
- 491
4
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3
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787
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How does this LLC converter keep 50% duty cycle and zero DC offset with AC-coupled feedback?
I'm currently designing an LLC resonant DC/DC converter with 12V input, +/-15V output and nominal 200W combined output power. I've already got my resonant circuit, transformer, gain curves and power ...
- 20.5k
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3
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514
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How is voltage difference of input terminals zero in open loop ideal op amp?
An ideal op-amp has infinite open loop gain. This means that the input voltage difference approaches zero. What causes the difference to go to zero in the absence of negative feedback?
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1
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Modeling first-order dynamics of a switching converter
I have created a simple, first-order model of a switching regulator in steady state (it's basically a transformer with a loss element). Its only parameters are desired output voltage \$V_o\$ and ...
- 1,332
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0
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111
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Discussion on demonstrating saturation in operational amplifiers with positive feedback, and simulation problems
I have been dedicating my time to the study of Operational Amplifiers for the past few weeks.
I understood that an amplifier in an open loop configuration has a very high gain, in the case \$A \to \...
- 207
1
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1
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301
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How does a capacitor-crystal-capacitor π-network produce a 180° phase shift in a Pierce Oscillator?
The Pierce Oscillator consists of an inverting amplifier, a crystal in parallel with a biasing resistor as well as two capacitors connected between the legs of the crystal and ground, as in the ...
- 160
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5
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513
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How can negative feedback reduce distortion if A*beta>>1?
I have read that negative feedback reduces distortion (frequency, amplitude, phase) because if \$A \times beta >>1\$ the transfer gain will be \$(A/(1+A*beta)) = A/A \times beta=1/beta\$. Which ...
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1
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645
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Preventing op-amp outputs from affecting one another
I built this op-amp circuit that takes in 4 inputs and outputs 3 sums by using op-amp adder and difference circuits to achieve a gain of 2x. In a simplified circuit, I boiled it down to the bare op-...
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1
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713
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Add negative feedback to this 2-stage amplifier
I am designing this 350mW 2-stage amplifier. The amplifier has only a voltage amplification stage Q2 biased with a current source Q1+Q3, a buffer Q6 and an output stage Q4+Q5. The input will be an ...
- 297
2
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1
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1k
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Emitter Follower / Common Collector as Negative Feedback Amplifier
Background
From the wikipedia page on Common Collector Amplifiers there is paragraph describing how the circuit acts as a negative feedback amplifier
The circuit can be explained by viewing the ...
- 1,008
2
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1
answer
889
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Implementing negative feedback on a JFET amplifier
I have started designing and simulating a simple Jfet amplifier using LTSpice.
The circuit I have below seems fine, apart from too much gain for my needs (about 20x to much gain).
To fix this, I ...
- 167
0
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2
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535
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Problem in controlling the device temperature using an op-amp
OBJECTIVE:
I have a device to which voltage is applied and this voltage has to be controlled according to the temperature detected by the thermistor that is placed on the device. If the temperature of ...
0
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1
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402
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I need help deriving the cutoff frequency of a negative feedback amplifier
I have the question and answer below for deriving the closed-loop cutoff frequency of a feedback amplifier circuit. I can follow the working out all the way until the last 2 lines, where the writer ...
- 157
1
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2
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791
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Why is this the voltage gain formula in the two-stage feedback amplifier?
In Albert Malvino's "Electronic Principles", he said that in a well-designed two-stage feedback amplifier for small signal operation(picture below) , the voltage gain equals $$A_v=\frac{r_f} {r_e}+1$$
...
- 1,074
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283
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Discrete-Time versus Continuous Time analysis of feedback system
Imagine a generic feedback system, where A is forward gain and F is feedback gain. I will now go over two cases where in i will analyse this system.
1. Reference = 110, A=10, F=1
In this case, it ...
- 106
1
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74
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Simple Stability and Feedback
I have a question, my book says that for the system in this picture:
If the system has G(s)*H(s) with a module of 1 (0dB) and a phase of -180°, the system is in Simple Stability, so it is like in ...
- 337
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2
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1k
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Op - Amp: Linearity, Negative Feedback and Virtual Short
I need some explanations about Linearity, Negative Feedback and Virtual Short for an ideal Operational Amplifier.
Precisely, I have been always told that an operational amplifier with negative ...
- 3,590
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1
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299
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Question about the slew rate
Let's consider an op-amp:
From basic courses of electronics, we know that the output voltage as a function of the differential input is given by the following picture:
Now, assuming that:
the op-...
- 616
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3
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443
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Unity Gain Buffer Initial Conditions
simulate this circuit – Schematic created using CircuitLab
A typical way of analysing the unity gain buffer is:
Where A is Open Loop Gain
Vout = A(Vin - Vp) and Vp = Vout therefore
Vout = A(Vin ...
- 1,008
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1
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177
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How to select resistance to cancel offset output voltage due to bias current?
Consider the figure above how Rcomp was choosen. I know for simpler circuits
like inverting amplifier and ideal integrator how Rcomp was calculated but following same procedure (that's using ...
- 475
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583
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What is topology of feedback for circuit?
I am confused between Voltage Shunt and Current Shunt Also mention why R2 shouldn't be considered as feedback as it is emitter degeneration resistance
Consider the above circuit why can't I consider ...
- 475
1
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1
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278
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How to prove that a circuit has negative feedback?
Queries regarding this circuit:
I am able to say that this circuit has negative feedback but my procedure is disorganized. I want a step wise procedure to identify the polarity of feedback.
In this ...
- 475
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0
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53
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What will be vo/i for given circuit?
Solve using both approaches first using small signal analysis and then using feedback analysis.
- 475
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0
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280
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What will be small signal trans resistance gain of shown circuit?
Take beta = 99.
I analysed this circuit using first considering this circuit as feedback circuit with shunt-shunt type of feedback and then did the same analysis considering that the circuit is a ...
- 475
0
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1
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696
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How do I find this value for the feedback fraction?
How exactly do I find this value for the feedback fraction Beta? Thank you. \$\omega_0\$ here is the natural frequency calculated as \$\omega_0\$ = 1/RC and s is the complex frequency.
- 101
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250
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How is this series series feedback topology forOPAMP?
This is stated as series series type of negative feedback but why.
Whereas this one is series shunt topology
- 475
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3
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2k
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How to identify the circuit has negative feedback or positive feedback?
I am having difficulty in identifying whether feedback is negative or positive (i'm not talking about feedback topology)
My teacher told that there is a method in which, after deactivating ...
user141515
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2
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2k
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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 \$\...
- 2,800
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3
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How to calculate closed-loop bandwidth from open-loop parameters using feedback factor
I'm working through a past feedback analysis question for an exam and trying to calculate what the closed-loop bandwidth becomes given the open-loop gain \$|Av|=10^5\$, open-loop bandwidth \$B_{wo} = ...
- 869
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3
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2k
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finding open circuit voltage gain
below I have this schematic to find the open circuit voltage gain. This circuit basically utilizes three resistors from which R_f is supposed to be the internal feedback resistor. It also utilizes the ...
- 299
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1
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Series-shunt feedback analysis
Microelectronic Circuits by Sedra/Smith present a method to analyze series-shunt feedback circuits by separating the 'A circuit' from the 'B circuit' in which h11 and h22 are consolidated into the 'A ...
- 1,187
7
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5
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879
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Is transistor in cutoff?
In the following circuit, consider the op-amp to be ideal (gain = ∞ , input resistance = ∞) and transistor beta is 20 A/A
Initially I was using virtual ground concept here but in the given answer ...
- 71
2
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2
answers
5k
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Individual Phase shift provided by Op-Amp in Closed loop configuration
When comparing the input and output of the Op Amp alone (Vid1-Vid2 and Vo and not Vsupply and Vo) in a closed loop configuration the phase shift is only 90 degrees? Why it is so?
And the Simulation ...
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