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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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How can I avoid saturation in current source amplifier?

I'm designing a class d amplifier with current feedback as in figure below with the following features: Vbus=50V Iout programmable from 100mA to 1A rms Vout=35Vrms max When the load overcomes the ...
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How Replica Feedback bias circuit rejects supply noise?

I attached the circuit diagram along with a short description of its working principle. However, it's not clear how the circuit rejects supply noise. It will be great if someone can brief about what ...
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46 views

Output impedance of a series shunt feedback amplifier

I am trying to find the output impedance of a series shunt feedback amplifier by converting it to a two port network. I know the input impedance: Ri=ri*(1+A.β) But I dont know how I should find ...
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47 views

Feedback Circuit schematic to Control Theory block diagram?

I'm studying analog electronics circuit with feedback. I see that, during analysis, a useful abstraction over the schematic is the block diagram in control theory style, but I stuggle in deriving it ...
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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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74 views

Difference between two integrator circuits

What is the difference between the two integrator circuits? They are used in an amplifier with feedback. There's heaps of information online about the one on the right but not so much about the one on ...
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60 views

Finding the negative feedback loop in the amplifier circuit

Today I was learning about the negative feedback in the amplifier circuits and some quick ways of discovering whether a negative or a positive feedback exist in the circuit by finding a feedback loop ...
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2k 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?
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17 views

CMFB - wide devices reduces voltage drop?

In the above CMFB using triode devices, one of the drawbacks is stated as being a limited output swing due to the drop of the triode devices (acting as resistors) M7 and M8. It says in the ...
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How to identify the feedback topologies?

It is extremely important to identify the feedback topology first before starting analysis. However, I find it difficult and cannot get it right. Is there an accurate yet easy way for me to identify ...
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100 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 \$\...
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Which CMOS logic families can safely be used to construct linear circuits?

I've just learned that digital CMOS inverters can be configured to perform analog functions (most notably oscillators and amplifiers). However, many of the examples tend to favor old CD4000-series ...
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40 views

How does not using common-mode feedback drive my outputs to the rails?

Consider the following circuit in Fig 9.31 (a) Now, essentially, summarising the block of text, it seems that due to some mismatch between PMOS and NMOS devices or fluctuations in bias voltages, the ...
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How to decouple a negative feedback loop in DC?

My question is open ended, but I provided an example to explain the question better. R19 and R8 in the middle of the pic form a negative feedback loop. They set the gain of the amplifier. I need to ...
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87 views

Homemade EEG Circuit Common mode feedback

https://sites.google.com/site/chipstein/home-page/eeg-with-an-arduino/assembling-the-arduino-eeg-circult Hi, I am currently building a DIY EEG circuit using the guide above. This guide is for when ...
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53 views

Explanation on why there is no feedback in the circuit for higher voltages of input signal

simulate this circuit – Schematic created using CircuitLab I don't understand the reasoning behind the analysis of this circuit. The professor started by saying that if diodes D2 and D5 are ON ...
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116 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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101 views

loop gain, open loop gain of op amp in inverting configuration (feedback capacitor)

I was trying to understand the 2nd answer from this post here, with the circuit of the post shown below. The 2nd answer has equations including open loop gain I wasn't able to understand (1st ...
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802 views

How do I implement a feedback to keep the DC gain at zero for this conceptual passive filter?

Regarding an example passive LC ladder filter, when I sweep the source resistance, Rs, the filter characteristics changes as follows as expected: On the other hand, if I sweep the load resistance, ...
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1answer
84 views

Analog implementation of imaginary roots in a transfer function

I have a simple boost converter, and from multiple papers I've read through, a Type 3 Compensator is recommended. I designed one in Matlab/Simulink, and it reacts very quickly. The problem is, when I ...
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138 views

Making block diagram of an op-amp configuration

Hi everyone, I have to make the block diagram of the above configuration. Supposing the input capacitance of op-amp Cin, I've drawn this: A is the open loop transfer function of the OPA. B is the ...
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57 views

Why does adding a capacitor to the adjust pin of a voltage regulator improve PSRR?

When looking into the datasheet of an voltage regulator, they often recommend adding a capacitor from the ADJ pin to ground, to improve ripple rejection. It can also often lead to an significant ...
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33 views

Feedback Block Diagram Reduction

For this diagram reduction question, I thought pushing the summing junction to the left past the G1(s) is can be a solution but is it correct that pushing to number 2 then we can collapse the summing ...
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107 views

Placement of feedback line on DC DC converter, before or after cap? (and dropout problem with LT8390)

I am using an LT8390 DC to DC converter, I have a highly inductive load and it is causing dips. The dips are shown here (and about a 6V drop for 7ms): I need to get rid of the dips, which I will ...
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37 views

Three level PWM modulator circuit feedback simulation

I'm trying to design a three level PWM circuit with feedback and i'm struggling to understand the feedback aspect. The design is based on this design by Texas instruments and modified to suit three ...
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2answers
4k views

Designing a PI controller for a first order system

I have a first order plant: $$ b/(s + a) $$ That I'm trying to control using a PI controller: $$ \frac{(K_ps + K_I)}{s} $$ I closed the loop with unity feedback to get this transfer function: $$...
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123 views

Calculating gain of ICF amplifier

I'm designing a circuit with an ICF (indirect current feedback) amplifier, and am trying to calculate the gain of the resultant circuit. Using the AD8237 I followed the example here when designing ...
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43 views

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
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1k views

Reason for small-valued feedback resistors in low noise Op Amp

I am wondering why the feedback resistor values specified in the datasheet of the AD797 are so small. My understanding is that the low feedback resistances keep the noise small, but isn't it also not ...
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1answer
52 views

Prevent current backfeed without power loss

I have a solar panel and an external power source feeding into a DC converter (U10) that are both used to feed a battery charger (U2): In a previous design I used 2 schottki diodes to prevent back ...
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1answer
64 views

Confusion of terminology for control systems

I am confused about the following definitions (if there are any): Reference input reference signal setpoint reference I don't understand specifically what they are referring to. Do they refer to ...
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1answer
89 views

What causes random ringing in my inverter?

I'm currently redesigning the inverter for driving my induction heater. While I've sorted out most problems I encountered I'm still struggling with the actual inverter. Picture 1 shows the waveform ...
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2answers
89 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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110 views

Stability of Feedback Amplifiers

I'm kind of confused above the stability of feedback amplifiers. Here's what I know In the notes, it says that I don't understand how that's true. I tried deriving it but didn't get anywhere
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60 views

Differential amplifier with feedback resistor

In this circuit, if a resistor of 1 M\$\Omega\$ is connected between A and B, what is the effect on the stability of the quiescent point? The analysis I made led me to believe it would provide ...
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47 views

Amplitude control in a signal generator

A am working on an FPGA based function generator and I am aiming for max frequency to be higher than 10 MHz, hopefully 30 MHz. I have implemented most of the functionality except amplitude control. ...
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2answers
2k views

How to suppress current spikes in transistor feedback loop

I am trying to pulse a load with a small constant current pulse (2mA @ 500us). The load does unfortunately have an unknown capacitance in the range 10nF - 1uF, parallel with an unknown resistance ...
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38 views

Negative feedback optical amplifier

Why the feedback network is necessary in this optical amplifier ? How the circuit would work without the feedback photodiode ?
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36 views

SEPIC vs. ZETA feedback

When I was reading through the RECOM book of knowledge DC-DC, I found out that the SEPIC converter has more chance of having resonance feedback than the ZETA converter. They mention that the SEPIC has ...
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175 views

Is static negative resistance practically available?

I learned that negative resistance (NR) could be simulated by involving active devices like op-amps and others. I'm interested in the static/absolute NR rather than the differential NR. My question is ...
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45 views

Avoid voltage feedback from laser psu to Arduino via pwm pin [closed]

I have been using GRBL software on arduino board for quite a while now, however the only issue I have is that the CO2 laser PSU kind of passes a small current back to the Arduino from its control pins,...
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How negative feedback increases the bandwidth

Negative voltage feedback affect all the frequencies equally. Hence by simple observation it is clear that, negative feedback doesn't affect the bandwidth of the circuit. But in many books, it is ...
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197 views

Why is current controlled feedback faster than voltage controlled feedback in PWM controllers?

Looking at modern ICs, we prefer current control feedback over voltage control feedback, due to the speed of the feedback. Current control will react faster than voltage control. Here are 2 images, ...
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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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34 views

What is the Correct method to find the poles and zeros expressions?

What is the Correct method to find the poles and zeros expressions ? This is a replica circuit method used to calculate loop gain, please only consider the above part. I used pspice to find the bode ...
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53 views

How to break this multistage feedback amplifier to find loop gain Aβ ? (I'm using pspice)

by hand calculation I know that loop gain Aβ of this (current-current) circuit is 30, I tried to break this circuit and add Vtest to it , and setting input to zero but I didn't get a result that match ...
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39 views

total transfer function of a LTI System with feedback

I have calculated the transfer function of such systems many times, but now i feel like I`m going around in circles. I have drawn a few help-signals to help me solve it, but they are dependent of one ...
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1answer
118 views

What is this NOR feedback loop in the AGC Cross Point Generator II?

This feedback loop looks similar to a LFSR, however there are no registers present. It looks to be some kind of oscillator. There seem to be three inputs to this component, ...
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140 views

Opamp with multiple feedback loops

I have been trying to figure out how the following circuit works and what it might be good for without any luck so far. What might the transfer function be? Is there a way that analysis can be ...
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2k views

Why do we get only one frequency as output in oscillators?

I am just into oscillators where I learned \$AB=1\$ for sustaining oscillations in positive feedback. Since \$A\$ and \$B\$ are both frequency-dependent, \$AB=1\$ is true only for a particular ...