# 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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### Finding the mid-band gain of an operational amplifier [duplicate]

I am studying for an exam. Been practicing on my professor's past exams and in this one I'm asked to find the transfer function and the mid-band gain. For calculating mid-band gain I'm assuming I must ...
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### Using Bode plots for locking a laser to a cavity

I am new to this topic, but I am trying to understand how to use Bode plots to optimize my PID loop parameters for PDH locking a laser to an ultrastable cavity. For simplicity (and based on what I ...
522 views

### Op Amp Feedback Resistors

When selecting feedback resistor values in operational amplifiers, how do you optimize the magnitude of the resistors? For example, I calculate the resistor 9/5 ratio value for a gain of 1.8 I know 5 ...
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### Given an active filter or any sort of operational amplifier with finite open loop gain, is feedback factor accounted for in the standard gain formula?

To be honest I don't know exactly what I'm calculating here, I know why I'm doing this but I don't know what this expression for gain is exactly. If I was dealing with an ideal opamp, it's consider a ...
1 vote
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### What happens when the feedback loop is also connected to the non inverting input in an op-amp

I am trying to understand this tone control circuit in a guitar pedal. The image was taken from https://www.electrosmash.com/tube-screamer-analysis: I do not know how to think about that feedback ...
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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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### Forward-Regulator Feedback

I used this circuit diagram section from TI documents and this is feedback for a PoE controller in forward topology and I read somewhere that resistor R18=50ohm is used to have Bode-plot of circuit. ...
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### Applying a voltage by DAC to a Feedback pin of a DC-DC controller

I want to design a variable output voltage in the following design: For having this variable voltage either I can use a potentiometer instead of R13 or I can apply a voltage by DAC to the feedback pin:...
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### What's the deal with this comparator's hysteresis?

I have here a circuit designed by someone else to create a 50% duty cycle square wave that leads a current transformer in phase. The CT maxes out at about 1 amp, and the output of the phase-leading ...
1 vote
63 views

### Can this oscillator possibly work?

I am trying to build a crude RF oscillator. My first attempt, though it simulated fine, disappointingly did not oscillate when soldered together. So, to debug this, I reduced the simulation example ...
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### Zener instead of resistor divider on dc-dc converter feedback pin

This dc-dc converter steps up voltage from 3.1V to 7.5V. I'm curious about the unusual D2 zener + R3 resistor to set the output voltage, instead of the traditional resistor based voltage divider. I ...
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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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1 vote
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### How to simulate a uniform distribution around zero in LTSpice?

I am using LTSpice for a Monte-Carlo simulation, I typically use the function {mc(x,y)} for componant variability I also want to introduce spread in the feedback ...
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### Op-Amp oscillations when controlling P-MOSFET Vgs

My background is digital design, I guess the answer is obvious for all here, but not for me. I am studying example of analog physical layer for USB 2 protocol which I found in this paper. Also ...
1 vote
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### Why don't we use an integrator as the loop filter of a PLL?

In a book on phaselock that I was reading, it mentioned that ideally, one would use an ideal integrator as the loop filter of a PLL. Since we can implement integrators with op-amps, why don't we use ...
408 views

### Where is the phase shift on this oscillator?

I didn't think the oscillator below could work, but I built it, and it does: I used 10 uH for the inductor, 2.7 nF for the capacitor, and got oscillations around 8 MHz. The feedback loop is a series ...
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### What requirements of a feedback network are needed to produce oscillation?

I'm trying to understand how to analyze simple oscillators, and would like to know if my conclusions about the required feedback network are correct: The simplest way to build an oscillator is with: ...
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### LTSpice simulation produced different results of phase margin when using step-signal % overshoot technique vs loop analysis technique

I am working on a class AB amplifier circuit to that can output both AC and DC current, controlled by an op-amp with feedback from the final output. The output will be driving an 50uH inductor. The ...
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### How to solve non-ideal opamp circuit using feedback properties?

Is there a neat way to solve this using feedback properties? Or if you know a better method to solve this, please suggest one. It would be straightforward if we assume an ideal opamp in this case, ...
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1 vote