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Questions tagged [feedback]

Feedback is a process whereby information from an output of a signal is used (intentionally or unintentionally) to alter the input of the same signal. Commonly used in operational amplifiers. An everyday example is the high-pitched audio frequency heard when a microphone picks up audio from its own amplified output.

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2answers
614 views

Oscillating system via negative feed back?

The Barkhausen criterion for system with positive feedback (being \$B(s)\$ the feedback network transfer function and \$A(s)\$ the gain network transfer function) afirms that for a system to keep ...
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Four transistor/full bridge version of the Royer oscillator

For some time now, I have been trying to figure out what (in theory) would be the most efficient way transfer power across a transformer. Applications include high voltage power supplies and induction ...
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151 views

Interesting Op Amp issue

Good board - bottom view Good board - top view Bad board - bottom view Bad board - top view I am new here and mainly a hobbyist when it comes to electronics. I work more with electricity than ...
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1answer
56 views

Phase shift near saturation mitigation in input stage amplifier — How does this work, why does this work?

I'm trying to understand how this circuit works on the input stage to the 4192A Impedance Analyzer. Apologies for the quality... this is the best scan I could find. The design is furnished with the ...
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1answer
506 views

Unrecognized and ignored parameters in LTspice while adding a Third-party model

I have tried to add a third party model to my LTspice program (2016 version) but when I run the simulation many errors show up. The model is made for PMOS and NMOS ( saved at the same link) Link of ...
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A question about positive feedback resistor in a Schmitt trigger

In many tutorials when explaining hysteresis what I read that when the output is high R3 becomes in parallel with R1; and when the output is low R3 becomes in parallel with R2. Above is a depiction of ...
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991 views

In closed loop configuration of op-amp,what happens to open loop gain?

Open loop gain comes from the internal circuit of op-amp which is very high, but in closed loop configuration the gain is limited by the feedback resistance. So my question is: What happens to open ...
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630 views

Input stage of a current mirror circuit

I'm trying to understand current mirror circuits and I've been reading this article. I'm unable to understand the input part of the circuit where the author says "Producing the opposite where the ...
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34k views

Why do I get feedback in my speakers in my car? [closed]

I have a Galaxy Nexus which I have with my everywhere. One of my favorite uses of this device is to play my music. Unfortunately, I have noticed something bothersome and I was wondering if I could get ...
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1answer
8k views

Feedback loop-gain(beta) derivation for the inverting amplifier?

During my study on the negetive feedback concept, i observed that the beta derivation for the non-inverting amplifier is so evident which is just a potential divider voltage.But i am unable to find ...
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8k views

Stability and loop gain of negative feedback systems

When we look for stability of a feedback system, why do we only concentrate where loop gain is unity and check the phase margin there. The phase of the closed loop system might be passing through 180 ...
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615 views

Selecting a capacitor for use in feedback loop

I'm designing a DC Lab Power Supply; the voltage regulation circuit looks like this: I'm developing the BOM, component by component, and next in line is specifying the capacitor in the feedback loop ...
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4answers
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How do crystal oscillators work with feedback consisting of CMOS inverters?

For a crystal oscillator to work, there must exist a feedback path with properly designed specifications in order for all to work as expected. Broadly, the basic form of this control system is as ...
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Why isn't IC1 a comparator?

This is with reference to a circuit i saw in The Art of Electronics.The authors claim that IC1 is an integrator and that the circuit ensures that a current of magnitude |Vin|/(200k) constantly flows ...
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CMOS inverter with feedback

In some circuits such as crystal oscillators, there is a CMOS inverter with a feedback resistor, they all simply say the resistor bias the 'amplifier' and force it to operate in the linear region, ...
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232 views

Resistive T-network

Can someone explain to me why this negative feedback resistive T-network simulates a 10M ohm resistance ? The overall closed loop gain is -100 because 10M/100k = 100.
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How is this circuit providing solution of the differential equation d^2 v/dt^2 = -9v?

Book pages at https://books.google.co.in/books?id=d-7owi6uNtMC What I see is that they have taken d^2 v/dt^2 as an input at point A, integrated it to get dv/dt, integrated it again to get v=2sin3t V,...
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341 views

effects of feedback on noise and non-linearities

This video lecture (start at 32:01), the professor showed a demo about the effects of feedback on noise and non-linearities. The graph below is a system with input signal which is applied directly ...
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1answer
911 views

What is an “origin pole”?

I'm studying Christophe Basso's book Designing Control Loops for Linear and Switching Power Supplies. In the book, he often uses the term "origin pole". This is what I think I understand about it so ...
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3answers
289 views

How do I determine \$R_o\$ for an op amp?

I understand that when driving a capacitive load with an op amp, the output resistance, \$R_o\$, of the op amp interacts with the load capacitor to form a low-pass filter, introducing a pole in the ...
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2answers
946 views

Polarity of feedback for a mosfet circuit

I came across this question in "fundamentals of microelectronics" The objective is to find out the polarity of the feedback. Could someone help me with this? My approach to this question is as ...
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3answers
1k views

What is the drawback of a high-value resistor for positive comparator feedback / hysteresis?

I'm building a simple circuit which has an LM211 comparator at its heart. The positive input is connected to a 10k-10k resistor divider across the supplies, stabilized by a 1uF capacitor. Hysteresis ...
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2answers
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Why can't a feedback network use a capacitor? [duplicate]

Possible Duplicate: Basic Frequency Control Circuit In the following schematic, why can't R4 be taken away and the feedback network pass output feedback through C2 and R2?
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220 views

Why do two transfer functions of a circuit have same denominator?

I am investigating a linearised common-emitter circuit of the form: simulate this circuit – Schematic created using CircuitLab I am interested in the isolated transfer functions of each input ...
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4answers
421 views

Voltage buffer with ideal Op-Amp (positive feedback) - Instability

I know that the circuits which employ negative feedback are stable, whereas those which employ positive feedback are not stable. How can I prove that a voltage buffer (ideal op-amp) which uses ...
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2answers
461 views

Why do transistor transmitters not have base resistor connected to collector instead of vcc?

I was researching here on transistor amplifiers: http://www.talkingelectronics.com/projects/TheTransistorAmplifier/TheTransistorAmplifier-P1.html#Stage and they were talking about these two ...
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1answer
79 views

Transimpedance Amplifier Gain Analysis

I'm trying to go through a mathematical gain analysis of a closed-loop transimpedance amplifier circuit, but I'm having issues trying to relate the block diagram to the actual circuit. simulate this ...
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2answers
103 views

Question about differential signals and feedback

Let's consider, for example, this circuit: During lessons, our professor always assumed perfect differential input (two signals with the same dc value and with equal and opposite amplitudes). As a ...
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490 views

Collector feedback resistor amplifier q-point

Why the Q-point of an amplifier with collector-feedback resistor are stable and not randomly moves on output BJT-curves when the power supply in applied to the circuit? The schematic is below:
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960 views

How does using negative feedback in biasing stabilize the beta of a BJT?

As far as I know the only reason beta is not reliable because it is temperature dependent. I have seen some diagrams about biasing to obtain stable beta. I read the negative feedback provides this ...
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681 views

working principles of Electronic Throttle Body

Could someone shed some light on a working principle of this Electronic Throttle Body from MagnetiMarelli? (Found in BMW R1200GS motorcycle). Seems to be contactless feedback via the 4 tiny pins. ...
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3answers
253 views

How is opamp gain calculated in this circuit?

How do I calculate the gain on each stage in this circuit? I see a feedback but no Rg. So here's the simulation of the fist stage of the above circuit (Replaced the MAX4477 by a LT1395). Thanks guys,...
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1answer
794 views

How does this sample and hold circuit work?

What role does the 30k resistor play in the LF398? How would that resistor eliminate any offsets introduced by the op-amps in a circuit like this one: On this ...
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535 views

Instrumentation Amplifier with Common Mode Feedback output

I'm currently attempting to design a small circuit that takes in a differential signal at < 4mv. I want to amplify this by around 1000 times. I was reading up on Instrumentation Amplifiers, and ...
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2answers
112 views

Positive and negative feedback in opamp in same circuit

In our class we encountered several opamp circuits, for example, Non-inverting integrator: simulate this circuit – Schematic created using CircuitLab or we can consider the sallen-key type ...
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1answer
79 views

Question about the common mode

After introducing the two-stages op-amp and frequency compensation for this circuit, during lecture the Professor asked us to find as an exercise a possible polarization of the following circuit: in ...
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122 views

Proportional Control Balance Beam

Bit of an unorthodox question I'm sure, but I'm making a balance beam (two rotors on either end of a see saw) with proportional control, and I can't seem to get it to balance at 0. The proportional ...
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221 views

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 ...
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2answers
463 views

Feed-forward capacitor in SMPS feedback

I was looking at the TPS63700 DC-DC inverter datasheet and stumbled across the schematic below. It is a more or less usual buck-boost inverter topology schematic, except for the weird R4 and C3 ...
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1answer
1k views

Transistor latch circuit - what's the capacitor for?

I've been studying this transistor "latch" circuit over the past couple of days and I think I've grasped most of it, but I'm not sure about the purpose of capacitor C1. https://circuitdigest.com/...
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1answer
342 views

Current amplifier with Mosfet and Op-Amp: Output resistance

In the following circuit, why is \$R_o\$ given by: \$R_o=(R_1//R_2)+r_{o2}+g_m .r_{o2}.(R_1//R_2)\$ ? I dont understand the \$g_m .r_{o2}.(R_1//R_2)\$ parcel
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1answer
510 views

understanding oscillation in op amp circuit

I understand what causes oscillation in a negative feedback op amp circuit- when an op amp circuit is not stabilized to have its AB<1 at the frequency whose phase shift is 180, then the negative ...
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1answer
526 views

stable/unstable equilibrium point in inverter with feedback circuit

I am reading about ring oscillator here (from page 4) and was stuck at the concept of stable/unstable equilibrium point. How to know if an equilibrium point is stable or not? For example, the middle ...
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1answer
650 views

Representing feedback circuitry as two-port networks

I'm taking an electrical engineering course and we are covering the effect of feedback on the bahaviour of amplifiers. I learnt the 4 basic topologies, and how with each configuration the feedback ...
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1answer
268 views

Does the stability of a circuit depend on its feedback topology?

I am reading an article entitled "A Comparison of Two Approaches to Feedback Circuit Analysis" here. If I understood the author correctly, we use return ratio instead of two-port loop gain analysis ...
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2answers
1k views

Common Emitter Colpitts oscillator

Good day, we were tasked to design a transistor based RF oscillator to be used as a VCO for our design experiment. In the picture shown below I have seen many tutorials on how to set the L1, C2, C3 ...
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1answer
1k views

Why Bandwidth Affects Response Speed

This is a follow-up question to (this question). Here is the amplifier section in question: In the answer, the author (@Brian Onn) gives the following explanation: "Slow vs. fast is not about the ...
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69 views

Gain of Basic Amp with FB network

the goal is to find the gain of the circuit. I don't understand the Vi/Vs part. I know they used voltage divider, but why they included the second term(in Red) in the expression? where does that come ...
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Input impedance of a non-inverting op-amp

From what I've read (and simulated), the feedback loop of an op-amp modifies the input impedance of the non-inverting input. The value specified in the datasheet is the open-loop input impedance, and ...
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1answer
909 views

Intuitive explanation for this hysteresis circuit?

simulate this circuit – Schematic created using CircuitLab I am trying to get an intuitive understanding of this small circuit. I have both breadboarded it to look at behavior on a scope and ...