Questions tagged [negative-feedback]
The negative-feedback tag has no usage guidance.
196 questions
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Negative feedback perspective on SAR ADC
A SAR ADC resembles a negative feedback system. The comparator input is a summing node.The difference between the analog input and the DAC output is the error signal which is driven to zero by the ...
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How is this op amp in negative feedback?
I'm trying to solve this question for homework but they mentioned the first op amp is in negative feedback. How though?
Is it because of the output of the second op amp (OA2) is also in negative ...
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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 ...
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Would it be possible to cap the output voltage of a Joule Thief using feedback from linear regulator ground pin?
Please bear with me if this is a stupid question, I made about 5 functioning circuits in my life.
I am making a simple tool that beeps when it detects water. I am using attiny13 microprocessor (it's ...
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How is an inverting opamp adder circuit able to regulate its feedback?
Consider the typical opamp inverting adder as follows:
Why don't resistor Rl and R1 form a resistor divider and impose 2.5V upon inverting node and drive it to saturation. How is opamp's feedback ...
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Potential ground loop issue in DC-DC common ground circuit
I am trying to setup a dedicated battery for my dash-camera, this will provide continuous power when the ignition is OFF and has a manual NC switch to turn off the circuit when not needed.
I ...
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What is causing the spikes at the negative terminal of the opamp in response to the square wave?
I have a simple inverting amplifier as following in which the input is a square wave. By virtual short I expect node VF2 to be at 0V, but when I plot the voltage at VF2 I see spikes that are in sync ...
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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 ...
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Infinite output impedance in amplifier, instead of 0?
The question asks: "Exercise 14.5 Assume an ideal op amp and use the summing-point constraint to find an expression for the output current io in the circuit of Figure 14.14. Also find the input ...
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How are opamp node voltages being set in the following circuit and what is the use of the diode configuration?
I am using a PCB which has the following opamp configuration implemented. It's supposed to be a precision buffer for the source V3. I accidentally connected the source V4 as well and observed strange ...
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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 ...
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Why input signal of negative feedback amplifier is Vs - Vf?
The block diagram below is from my textbook. I don't understand why the input voltage Vi = Vs - Vf. Take an example as the image with numbers on it, I know its not correct in reality but just assume ...
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Why can't the following configuration be considered negative feedback?
In the following circuit I have kept the resistor ratio such that beta factor of negative terminal (part of output will come on inverting terminal by voltage division), is higher than that of positive ...
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Unity Gain Amplifier Purpose
In layman terms, what is the main use and purpose of unity gain amplifiers? I am reading that it is used to "buffer high impedance sources" but I'm unsure what this means practically.
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Input/Output Impedance for ALI
Consider these circuits from Paul Horowitz "Traité de l'electronique" page.238:
I want to derive the expressions they made for \$ Z_e, Z_s \$ for both circuits:
So I think the op amp is ...
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Negative feedback amplifier
The following circuit diagram is from a book on electronic circuits. The Current source \$I_s\$ is driver of the amplifier. It was written that this amplifier has negative feedback. It seems that if ...
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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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How to prevent this op-amp from railing
I have the following circuit:
An input that can go negative (+/-5 V sine wave), and two inverting op-amps. The second op-amp is "current buffered" and is driving the base of a BJT.
Here is ...
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What are the necessary conditions to prevent latch-up problem for Oscillators?
In his chapter on oscillator design, Razavi discusses the issue of latch-up and proposes several methods to eliminate it. However, he doesn't provide explanations for these methods. Could anyone ...
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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 ...
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The influence of negative feedback on input resistance and bandwidth
I'm interested in how negative feedback affects bandwidth and the cutoff frequency.
Is the cutoff frequency always increased by (1-Ab) times?
fg_r = fgo*(1-Ab)?
Does the same apply to input resistance?...
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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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Gain of a negative feedback circuit (problem)
I am asked to find the gain A for this negative feedback circuit below:
(A: gain, G: all of the gain of the circuit, F: return ratio)
The simplified circuit above shows the gain A that I am trying to ...
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Constant current source with transistor
I have this circuit that should describe a constant current source. From my point of view the pnp-transistor has to work in its saturation mode. Thus the potential on the emitter should be constant. ...
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Why, in a negative feedback amplifier, do the op-amp input terminals become virtually connected?
The equation from the model of the functionality of the op-amp is that
$$V_{out}=A_{0}(V^{+}-V^{-})$$
In case of negative feedback, \$V^{+}=V^{-}\$.
Why do the two terminals in case of negative ...
user344970
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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]?
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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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What is the purpose of including (or excluding) the output resistor in the feedback loop of an op-amp buffer?
I have often seen (and made) circuits like this. It is a simple inverting op-amp buffer, plus a small current-limiting output resistor to protect the the op-amp if the output is shorted.
simulate ...
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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 ...
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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 ...
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Minimizing noise with single-ended opamps
Opamps often get used with one input at a DC voltage, usually the main ground per the standard inverting amplifier example:
For low noise, a BJT input stage like OPA1611's is often chosen for the ...
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Linearity and speed tradeoff with closed-loop feedback
This article describes some tradeoffs involved with methods to increase an amplifier's linearity. One of the ways to increase a circuit's linearity is by applying negative feedback, which converts an ...
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Difference OTA and op-amp
I have a question about OTA (operational transconductance amplifier). Why can an OTA can be used without negative feedback but would still be able to keep its inputs (V+, V-) close each other? I have ...
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Measuring Inverting Op Amp config and not getting desired output (practice)
I am a year 2 EE student and I'm still struggling with getting simulations to work in practice.
Components:
10k resistor x2
Arduino
LM741 Op Amp (pinout: https://www.ti.com/lit/ds/symlink/lm741.pdf)
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Negative feedback in an opamp
I am a fresher and have been introduced to a basic electronics course at college.
Recently our professor was introducing us to opamps and was referring to negative feedback as a rectification to any ...
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Learning the Art of Electronics 9N.4 -- low-dropout voltage regulator
I have trouble understanding one circuit in section 9N.4 of the book "Learning the art of electronics" by Thomas C. Hayes. I attached a screenshot of that section below.
I understand the ...
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Parasitic oscillations for phase shift not equal to -180 degrees
From "Learning the Art of Electronics" by T. Hayes and P. Horowitz, Cambridge University Press (p. 360):
As per above figure, the LF411 op-amp imposes a -90 degree phase shift on output ...
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Regarding positive feedback and negative feedback of OP-AMP
My background knowledge
This picture is ideal OP-AMP:
where $$Vo=A(V_+ - V_-)...(0)$$
When I configure the non-inverting amplifier mode:
$$(V_i-V_o\frac{R_1}{R_f+R_1})A = V_o....(1)$$
$$V_iA=V_o+(\...
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voltage follower design question
Hi , I am trying to build a simple voltage follower circuit in IC. I have tried to build ideal Op-Amp as a transconductor. Now, it requires minimum bias voltage for it to operate as a transcondcutor (...
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Problem with Arduino MEGA and opamp LM741CN for feedback ammeter
I am trying to create a feedback ammeter using Arduino MEGA ADC and OpAmp LM741CN. In order to perform a proof of concept, I use Arduino MEGA, LED, and Resistor 1 MΩ, then I read its current with a ...
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How does negative feedback stabilize the output of an op-amp?
I am trying to understand how negative feedback stabilizes the output of op-amps.
It is known that Vout = AOL*((V+)-(V-)), where AOL is the open loop gain of the op-...
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Non-inverting op-amp
Why is resistor R1 connected to the inverting terminal of the op-amp in a non-inverting op-amp configuration? What will happen if we replace it with a short circuit?
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Op-amp 'overcompensation'
First, a bit of background; I'm trying to regulate a HV DC-DC converter using an op-amp with an NPN Darlington current booster. The DC-DC converter is a push-pull circuit driven at about 40 kHz that ...
user194170
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Sensor datasheet shows op-amp circuit with capacitor to ground from inverting input. How does this work?
In the circuit above the inverting input feeds to ground through a capacitor.
The output should be a constant voltage used for reading into an ADC/taking a measurement.
A negative feedback op-amp ...
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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 ...
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Op-amp clarification in table
I'm using this Op-amp with Vcc of 5V and GND, voltage follower configuration.
Input to the non-inverting terminal is 0-2V (from a DAC). Output pin is connected to the inverting terminal.
Since, it's a ...
user220456
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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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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 ...
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Block diagram of inverting amplifier
I want to draw the block diagram of a generic inverting amplifier.
simulate this circuit – Schematic created using CircuitLab
Question: What is the actual block diagram for an inverting ...
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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 \...
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