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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 ...

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45 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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31 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
102 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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1answer
106 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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4answers
104 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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6answers
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 ...
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0answers
28 views

how C2 leads to negative feedback and C1 leads to positive feedback

C1 and C2 represent stray capacitances. I was told that C2 leads to negative feedback and C1 leads to positive feedback (pg 371 of Learning the Art of Electronics) and therefore C2 is good while C1 ...
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24 views

Breaking feedback resistor

I need to find the input/output impedances of this circuit (both open-loop and closed loop). I'm not sure how to deal with the Rf resistor as it lies in the middle. I was thinking to use the Miller ...
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1answer
27 views

Find gain of this common-gate

I have a large circuit involving feedback as follows I am trying to find the closed-loop gain of this. Before I can do that, I need to find the open-loop gain. Thus, removing the feedback loop, M2 ...
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0answers
43 views

Low Battery Relay

I need to detect SLA battery voltage & when the battery comes closer to 10.5V the relay must turn ON.The below circuit works ok, but the hysteresis gap is pretty closer, when I touch the circuit ...
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2answers
43 views

Why is the gain of feedback amplifier Vo/Vs?

Amplification = Output/Input Then the amplification of the feedback amplifier should be Vo/(Vs +- Vf) Here, Vf = feedback signal Vo = Output signal Vi = Input Signal and Vi = Vs +- Vf Vs = ...
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39 views

Convention of closed loop gain in op-amp for inverting configuration

I tried to analyze real op-amp equations, in inverting and non-inverting configurations. I found a reference question here in which they were calculating exactly what I wanted to do: calculating the ...
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1answer
51 views

Active Integrator Parallel Capacitor in Feedback

I am designing an integrator circuit, looking to perform in the range of 10-10kHz - and I had a thought and I cant find any information online about it. For low frequencies of 10Hz, the reactance of ...
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1answer
73 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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1answer
95 views

Designing two stage CE amplifier with negative feedback [closed]

I'm trying to design two stage ce amplifier with negative feedback using 2n2222 transistors. The circuit must have certain voltage gain, Rin, Rout, Vcc, low and high frequency filter. This is the ...
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3answers
141 views

Inverting OpAmp with voltage divider in feedback loop

Last week I was looking for a programmable gain amplifier (PGA) with high gains (> 100V/V) and low noise. As far as I know most of the PGA integrated circuits out there are just (inverting) amplifier ...
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2answers
49 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
30 views

VFA vs. CFA Compensation Capacitor Comparation

Here, I am referring to voltage-feedback amplifier (VFA) and current-feedback amplifier (CFA). A basic schematic is given below for each. I.) VFA II.) CFA I am curious about the position of ...
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1answer
66 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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1answer
70 views

Op amp with feedback

simulate this circuit – Schematic created using CircuitLab How to calculate Iout(current flowing through RL) of this circuit? All Resistors are of same value except the load resistor. Let the ...
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1answer
78 views

Need help choosing resistors for difference amplifier

In the circuit below I am trying to achieve 15.56 gain on IC2. The following combinations (in kOhms) are fairly close: 20/1.3 or 200/13 = 15.38 47/3 or 470/30 = 15.67 51/3.3 or 510/33 = 15.45 56/3.6 ...
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1answer
94 views

Buffer OPAMP feedback resistor

I am using an LT1630 as a buffer... I know its not the greatest OPAMP for the job because it has fairly Hi input current, but It has good DC characteristic, HI current drive, and rail to rail ...
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1answer
44 views

speed control loop percent error

I'm having trouble understanding the percent error from the following closed loop feedback equations. \$w =1\$ is the road grade change and \$r=65\$ is the speed control input, and given closed loop ...
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0answers
30 views

Reduce Noise for Teensy Motor Shield with Audio Amps Design

I am currently working on a motor shield (2 layer PCB) for a Teensy 3.5 micro controller for a hobby RC car project. Both the shield and the MCU will be powered by a 2S LiPo battery. This is one of my ...
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2answers
98 views

Operational amplifier and negative feedback

Let's consider an op-amp. In every book I've read till now, it is said that if we have: negative feedback finite output then we have: Vout = A * (v2 - v1) --> (v2 - v1) = Vout / A If A is very ...
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49 views

Pspice overlap two wires without connecting them

I designed this feedback circuit in pspice. As you can see, there are some wires which overlap and should not be connected. As I found online, I tried to not place the overlapping wire over a ...
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2answers
773 views

Non-inverting op-amp configuration with capacitor

I don't really get what is the purpose of the capacitor C1 which is connected in parallel with the feedback resistor. After my knowledge, if we modify the input signal frequency the over all gain will ...
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1answer
61 views

Feedback Error Equation

I am currently digging into some amplifier feedback analysis tools papers and literature. I found some "term" right at beginning of this topic that I don't quite understand. That is "Error equation of ...
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1answer
52 views

In a closed loop system, when obtaining a bode plot why is the open loop transfer function used?

In a typical closed loop system, with G(s) as the forward function, and H(s) as the feedback function, why is the transfer function used to calculate the bode plot G(s)H(s) instead of G(s) / 1+G(s)H(s)...
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2answers
97 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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2answers
513 views

Controlling MOSFET's resistance using negative feedback

I wanted to use LM317 in a power supply project but wanted to control voltage digitally or with voltage. One possible way was to change one of the voltage divider resistors on the schematic below, ...
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1answer
120 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 ...
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2answers
255 views

LF356 integrator simulation using LTspice

I used the LTpsice to simulate the feedback performance of a integrator circuit with op amp LF356 which is a JFET input op amp but I go strange results (see the image below). The model of the LF356 ...
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4answers
93 views

why is the feedback or gate resistance RG necessary?

Here the large feedback resistance RG interposed between gate and drain of the NMOS (usually in the megohm range) forces the dc voltage at the gate to be equal to that at the drain (because IG = 0). ...
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3answers
342 views

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} = ...
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0answers
22 views

CSxCC stage, series-shunt feedback, identify sign of feedback

MY ANALISIS The stage is inverting x non inverting = non inverting. Shunt sampling since it perturbs the output current, Series mixing. Thus if a positive input voltage is applied, the output is ...
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3answers
200 views

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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1answer
420 views

Voltage regulator frequency range

I'm designing a new encoder pulses counter for my project, my encoder HE50B uses a 12-24 VDC Input, and it has 1,000 pulses per each revolution. also the maximum permissible speed is 5,000 RPM. Now I ...
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3answers
454 views

Block diagrams can be different and still works for the same system?

I am an telecommunications engineer who is working now as a programmer. At university we took a class on digital filters, Laplace transformation and working in the frequency and time domain. At the ...
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1answer
140 views

Transfer function of Op-Amp-Twin-T Filter

I have the following circuit and wanted to find out the transfer function of the whole circuit (which includes the non-ideal op-amp as well - modelled as a VCVS - H(S) is DC gain with some poles). I ...
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0answers
53 views

Would a current feedback op-amp work well as a precision ground reference?

I've been looking into precision ground reference circuits to form ±5V rails from a 10V supply for a project I'm working on, and noticed that current feedback (CFB) op-amps have some desirable ...
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2answers
247 views

Voltage Feedback Using TL431

Hello All , In the Above circuit , TL431 is used to regulate the output voltage which is set by resistors RH1 and RL1. resistor RB is bias resistor to provide the current to regulate the output ...
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1answer
67 views

Voltage feedback reference issue with buck converter

I've couple of questions regarding the buck converter. I've been trying to design a buck converter for MPPT circuit which is in Low side switching configuration, as shown in the below diagram. ...
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1answer
127 views

Common source amplifier, source degeneration and determining the cutoff frequency

I have a n-MOS transistor with the following biasing network: I have to determine the cutoff frequency due to GS and GD capacitances The method used by my book is to first redefine the ...
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3answers
75 views

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 ...
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1answer
366 views

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 ...
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1answer
58 views

Differential gain of an op-amp and feedback

In an op-amp, we know from basic electronic courses that vo = A(v1 - v2) Assuming large differential gain and finite output, we get that (v1-v2) is very very small, ideally zero. In a university ...
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1answer
41 views

Shunt feedback input impedance

I am trying to derive the input impedance for the transresistance amplifier (shunt feedback) on page 119 in the Art of Electronics. I am considering a voltage \$v_i\$ applied to the input. As ...
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1answer
140 views

Why CCVS feedback amplifiers are popular as RF buffers

I've been attempting to build a VCO recently (around 50Mhz) and I've reached the part where I need a solid buffer for my oscillator. Looking around at various options I can't help noticing that many ...
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1answer
49 views

current source with op-amp+NMOS

this is a closed loop feed back circuit in order to make a precise current source. my first question is about R23. haw much it should be? i think it is better to just mounted a 0R resistor and ...