Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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.

There are two basic types of feedback: Negative and positive.

Negative Feedback: When the output is used to attenuate or diminish the input signal. Commonly used to correct errors or limit levels to an acceptable value. Negative feedback occurs when the output is between 90 and 270 degrees out of phase with respect to the input signal.

Positive Feedback: When the output is used to amplify or enhance the input signal. Can be used to decrease sensitivity to small signals or noise. Positive feedback occurs when the signal is in phase with the input signal.

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Choosing resistor values for inverting amplifier and why?

The gain here is A = -Rf/Rin. However, lets say I want a gain of 10 V/V. Which resistor value would you choose and why? I know that you could have infinite number of combinations for these resistors but why would some one use specific value. i.e Rf…
dr3patel
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What is noise gain, really? And how is it determined in the general case?

UPDATE: This question triggered what might fairly be called a research obsession for me. I've gotten pretty close to the bottom of it I think, I've posted my findings as an answer below. There was a similar question here but it did not ask for nor…
scanny
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Why would you stack a resistor and capacitor on top of each other?

I've inherited an charge amplifier/shaping circuit from my predecessor. When he wanted to make a low-pass filter with current-to-voltage conversion, he had a standard circuit like: simulate this circuit – Schematic created using CircuitLab He…
Seth
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Side effects of using large resistances

Are there any problems that can be caused by using resistors of large resistances (in the order of megaohms)? I'm designing a feedback network that is just a voltage divider, and I want the feedback to drain as little current as possible from the…
Tendero
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Why is feedback required in op-amp circuits?

I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required. What is the purpose of DC feedback when using…
user1083734
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Stability (phase margin) analysis in real feedback circuits

So I had a bright idea of using negative feedback to control offset current in my data acquisition circuit. Sure, you could do this in software, but removing the offset at the input stage would reduce the swing and allow more gain in the pre-ADC…
Ben Voigt
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What does this circuit do? Op-amp with transistors in feedback

I'm an electrical engineering student and I find this circuit in a guitar amplifier schematic, and basically, I'm just wondering what it does, and how one would go about working out what it does. Like what approach do you take when you're…
user968243
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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 devices. In addition, this application note mentions…
Caleb Reister
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Step-by-step explanation of how voltage follower reaches steady state using negative feedback

Just one minute! I am not trying to understand what negative feedback does eventually, or why it should be used. I am trying to understand how the circuit reaches steady state, and how, step by step, the negative feedback causes Vout to be the same…
Hassaan
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How are positive and negative feedback of opamps so different? How to analyse a circuit where both are present?

In an opamp, feedback on the positive input places it in saturation mode and the output is of the same sign as V+ - V-; feedback on the negative input places it in "regulator mode" and ideally Vout is such that V+ = V-. How does the opamp change…
Mister Mystère
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What is the purpose of the positive feedback in this opamp circuit?

Consider: Attached schematic is from a broken sampling scope that I have in the lab. During the reverse engineering the module, I noticed that it uses positive feedback around U2. I understand that positive feedback is often used to implement a…
Emm386
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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 frequency. What happens to those frequencies for which…
Souhardya Mondal
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Virtual Ground Paradox?

I'm unable to come to terms with something I think is a paradoxical situation relating to the virtual ground of an Operational Amplifier.Please pardon me if this is a really stupid question. When the 'Negative Feedback' in an Op-Amp (Ideal) makes…
Sumanth
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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 one out of the following four feedback…
Sibbs Gambling
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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 written that negative voltage feedback increases the…
Jobin
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