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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 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 ...
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How does this Push-Pull amplifier work?

I'm reading about op-amp circuits that use negative feedback from this article (question no.19). What confuses me is that the negative feedback for the Op-amp (which is being used to reduce ...
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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....
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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 ...
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Basic Frequency Control Circuit

How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why? Here is the schematic which is ...
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How does a Miller cap physically create a pole in circuits?

If we consider a single NMOS transistor (with its source terminal grounded) and a Miller cap (C) between its input (gate) and output (drain) nodes, circuit theory says that this Miller cap will be ...
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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 ...
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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, ...
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Bandwidth of inverting and non-inverting op-amps

If the same op-amp is used in both inverting and non-inverting modes (with same closed loop gain using appropriate resistors), will the closed loop bandwidth of the op-amp in both cases be the same? ...
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Pass device selection for bench DC power supply

I'm designing a DC Bench Power Supply. This one will be 0-30V, 0-300mA, but I expect I'll try some heftier models once I've gotten this one worked out. I'm following the general design procedure ...
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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 ...
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What is this RC local feedback configuration?

I'm studying power converter control loops using Christophe Basso's book Designing Control Loops for Linear and Switching Power Supplies. A very common pattern in the compensator circuits is a ...
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Adding negative feedback to a common-emitter transistor amplifier

I am trying to learn how to implement negative feedback to a common-emitter configuration.The goal is to reduce distortion by sacrificing some of the gain. simulate this circuit – Schematic ...
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Negative feedback output question

What is the value of Vout if we know the value of Vin in this case? It is a buffer amplifier, but it has two extra resistors so I think that the gain is smaller than 1, but how small? (Vin-V3)/R1=0 &...
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372 views

Effect of zeroes in system stability

Suppose we have two third order systems (a and b), with three poles and two zeroes,poles for both the systems are at the same positions in frequency domain but these systems differ in the placement of ...
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feedback resistor

How to determine the feedback resistor in negative feedback op-amp configuration ? How does the feedback resistor affect the signal output of op-amp ? What is the consequence of using high resistance ...
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1answer
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Is it possible to make a non-inverting amplifier with positive feedback?

The 'classic' non-inverting amplifier configuration uses negative feedback. What happens when the + and - terminals are switched? Based on my pencil-and-paper analysis and a Circuitlab simulation, it ...
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1answer
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Feedback loop-gain(beta) derivation for the inverting amplifier?

During my study on the negetive feedback concept, i observed that the beta derivation for the non-inverting amplifier is so evident which is just a potential divider voltage.But i am unable to find ...
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Common emitter, o.p. set by feedback resistor

I am analyzing common emitter amplifier where operating point is set by feedback resistor between b-c. Voltage gain showed by symulator is much lower than (-)R2/R1 and input resistance is lower than ...
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Individual Phase shift provided by Op-Amp in Closed loop configuration

When comparing the input and output of the Op Amp alone (Vid1-Vid2 and Vo and not Vsupply and Vo) in a closed loop configuration the phase shift is only 90 degrees? Why it is so? And the Simulation ...
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Three stage feedback amplifier

In the following circuit, in order to obtain negative feedback, shouldn't we need A2 to be positive? Also, is the correct feedback topology current-current?
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1answer
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Why has this configuration chosen for feedback?

I'm a newbie in electronics and Trying to understand and build this circuit. would somebody tell me the rule of R1 & C2 in this circuit and their magnitude effect on the controlling of process.why ...
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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 ...
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Why are feedbacks connected to the negative terminal of op-amps? Example given

I ask this because when I do the nodal analysis for the OP amp in figure 3, I end up with the same results as the inverting amplifier, even though the inverting terminal in figure 3 is grounded. So ...
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2answers
362 views

What can be inferred from the frequency an op-amp is oscillating at?

For whatever reason, I seem to create a lot of oscillators in the course of developing circuits involving op-amps. I'm wondering if the frequency of oscillation, which normally appears to be quite ...
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Op amp analysis: when are the “negative feedback rules” applicable?

When we build op amp circuits that use negative feedback, like so: ... we can analyze the circuit very easily, by assuming that $$v^- = v^+$$ due to negative feedback (when also assuming the op amp ...
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1answer
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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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Positive feedback and unstability

In Wikipedia's positive feedback article it is stated that given the closed loop gain $$A=\frac{a}{1-af}$$ the system is unstable if \$af>1\$. I don't really get this. If \$a=10\$ and \$f=0.5\$ (...
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Input stage of a current mirror circuit

I'm trying to understand current mirror circuits and I've been reading this article. I'm unable to understand the input part of the circuit where the author says "Producing the opposite where the ...
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5answers
903 views

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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2answers
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BJT cascading amplifier

Im trying to analyze this piece of circuit and the feedback between the second transistors emitter to the base of the first transistor is confusing me. Does anyone have any ideas how to analyze the ...
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1answer
717 views

Simple Implementation of BiSS C interface for a position encoder

The BiSS C DB3 protocol interface for Absolute encoder is an Open Source and Free Communication protocol hardware compatible with SSI interface. It is used widely in absolute position encoders. ...
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3answers
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Why 60% overshoot with 55° phase margin?

UPDATE: Based on the answers I received, I got this working beautifully. There's a full outcome report in one of the answers below. I'm working through the design of an electronic load, basically a ...
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Input impedance of a non-inverting op-amp

From what I've read (and simulated), the feedback loop of an op-amp modifies the input impedance of the non-inverting input. The value specified in the datasheet is the open-loop input impedance, and ...
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1answer
255 views

How to adjust output resistance with galvanic isolation?

I need to control the device (lighting LED driver) with 0-10V input. It looks like the driver has 100 uA current source as it can be controled with 0...100% PWM, 0-10V or 0-100kOhm resistance: So I ...
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1answer
273 views

Confusion: Lock range of PLL

Suppose we have a type-I PLL whose block diagram is shown below: Here \$k_{pd}\$ is the average gain of the phase detector producing the control voltage \$V_c\$ which is input to the Voltage ...
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Chopper Amplifier feedback loop stability

I have a question regarding the stability of a circuit I plan on building. This is a voltage-controlled current source, with the IN-AMP being used to sense the current through Rsns and provide ...
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1answer
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Should I be concerned when loop gain rises back above 0dB on simulation?

Interim update Okay, I just realized I screwed up on the simulation. When I added \$C_{bp}\$ I upset the "break" in the feedback loop necessary to get the loop gain. The left-side lead has to go to ...
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Op-amp dominant pole bandwidth

I have been playing around with an op-amp design using TINA from Texas Instruments. I have selected the LM301A. TINA says that this op-amp has a dominant pole at 5 Hz. I have put the circuit ...
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2answers
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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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Delay and Stablity in Negative Feedback Systems: Confusion

Below is a block diagram that shows an op-amp in negative feedback with feedback network made from resistive divider: The encircled block is Op-Amp with 1 and 2 as its inverting and non-inverting pin ...
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Ring oscillator frequency

According to Barkhausen's criteria, for oscillation the feedback should be made after phase difference of 2pi and gain has to be >=1. Now when I consider a ring oscillator if 2 inverters are ...
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3answers
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BJT amplifier negative feedback question

This is a BJT amplifier we have learned I read from the book that the feedback type of it is voltage series negative feedback. I have 2 questions : If this is a negative feedback circuit how can ...
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3answers
242 views

How do I determine \$R_o\$ for an op amp?

I understand that when driving a capacitive load with an op amp, the output resistance, \$R_o\$, of the op amp interacts with the load capacitor to form a low-pass filter, introducing a pole in the ...
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2answers
525 views

Instrumentation Amplifier with Common Mode Feedback output

I'm currently attempting to design a small circuit that takes in a differential signal at < 4mv. I want to amplify this by around 1000 times. I was reading up on Instrumentation Amplifiers, and ...
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231 views

Calculating the transresistance in a multistage voltage-shunt(shunt-shunt) feedback amplifier

I've been trying to analyze the following circuit using whatever books and resources I have to hand: simulate this circuit – Schematic created using CircuitLab I've identified the topology as ...
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3answers
327 views

TIP127 + TL074 power supply doesn't work until I touch it

I have such a schematic based on the TL074 opamp and the TIP127 PNP darlington transistor to control the fan voltage (shown as motor near the D3 diode). VCC = 12V, VDIG = 5V generated by a LM7805. The ...
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Differential Amplifier with Global Negative Feedback

This question refers to audio amplifier design, using BJTs only. I am wondering how differential stage amplifier plays an important role in hi-fi audio amplifiers. According to this book (where ...
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4answers
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Current to Voltage Feedback Capacitance for SiPM

I'm having an issue with my Silicon Photomultiplier (SiPM) feedback circuit. The output is not behaving as expected. My board schematic is below: simulate this circuit – Schematic created using ...
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gain of opamp circuit with current output

I'm designing a current source using a MOSFET driven by an opamp. The opamp controls the gate by comparing the voltage on a shunt resistor to the input reference. You could say that the fet replaces ...