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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Two port feedback analysis of shunt-shunt amplifier with unity feedback

To consider the effect of loading in a shunt-shunt amplifier that is being analyzed with two port analysis, we short the feedback network at the input/output to calculate loading at the amplifier ...
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How to compensate this circuit? [closed]

I'm using the circuit above to control the common-mode voltage of the 2 resistors. M16 is a current source. The OpAmp controls common-mode voltage by adjusting the resistance of M20. I need to adjust ...
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Why will the offset of a source-follower which is connected to the output of an opamp as a voltage buffer limit the op-amp output swing?

I am currently reading chapter 12, "The Common-mode Feedback Circuit" in Analysis and Design of Analog Integrated Circuits by Gray and Hurst. Page 815, gives the following statement for ...
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Why does my MATLAB calculation/simulation differ greatly from my LTspice simulation?

Here is my circuit in LTspice. The frequency AC is here: This is DC with .op command. --- MOSFET Transistors --- Name: m1 Model: nmos-sh Id: ...
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Sine wave CMOS buffer from inverters with or without feedback

Is it possible to buffer a sine wave using inverters alone or with some kind of feedback? I've been browsing google for minimalistic (I'm in 3.3-12 V domain) sine wave buffers and this thought stuck ...
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How to analyse this with nullor block?

The first is the schematics from NMOS4 with parasitic capacitance: I recently read an article on how to analyse the circuit with The Nullor and Some Applications. The equivalent nullor circuit. I am ...
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What is the feedback \$\beta\$ for this resistor feedback?

The first is the schematics from NMOS4 with parasitic capacitance: What is the feedback \$\beta\$ for this resistor feedback? And Should we include the capacitor \$C_{gd}\$ for this feedback? The ...
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Stability test for Feedback Amplifiers

Does the following simple test deduced from Nyquist criterion also apply to positive feedback case or it needs to be modified? If magnitude of loop gain i.e. |T (jω)| > 1 at the frequency where ...
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why is my analysis for this resistor \$R_F\$ feedback network different from the book answer?

The following is from the book Design of Analog CMOS Integrated Circuit, page 313. Calculate the voltage gain of the circuit. (channel length modulation and bulk effect are neglected) At Node X with ...
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How can I get the same equation when using feedback loop analysis?

This is the circuit: Formula correction according to @Puk. (Shout out to Puk!) $$V_{in} g_{m1} + \frac{V_{o}} {r_{o1}} = (V_{in} - V_o) s C - \frac{V_o} {r_{o2}}$$ $$\Rightarrow \frac{V_o} {V_{in}} =...
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How to break the feedback loop and add the loading?

I am trying to break the feedback loop of a fully differential amplifier and add the loading to the input and output: I want to do this to take into account the loading of the feedback network on the ...
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Buck regulator's feedback voltage far lower than expected

UPDATE: Just found some weird behavior. When measuring VFB on the resistor pads with a voltmeter, I shorted VFB to ENABLE (4.36V) with the voltmeter probe. This caused the buck to start correctly ...
InBedded16's user avatar
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MP28167-A DC-DC converter recommends a resistor T-network in feedback loop

I am designing a DC-DC buck-boost converter using the MP28167-A, and the datasheet contains this section: I understand the need for a resistor divider such that the closed-loop control regulates the ...
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UC3842 optocoupler feedback confusion

I am having a slight confusion regarding the selection compensation pin of the UC3842 IC and the current mode control system given in the datasheet. Why is there an RC combination at the feedback of ...
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Why am I concluding that the emitter-degenerated CE stage is unilateral?

Consider the attached small-signal diagram for an emitter-degenerated CE stage: It's been a long day so I must be making an error, but I continue to conclude that this two-port is unilateral (defined ...
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Is feedback positive or negative for this closed-loop circuit?

The following is from the book Design of Analog CMOS Integrated Circuit, Page 307. I think feedback is negative in my opinion. Here is what I think, see picture below.
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Avoiding overshoot in step response for robustness

In Systematic Design of Analog CMOS Circuits (Jespsers, Murmann) page 343, the following is stated in the context of where to place the non-dominant pole in a second-order loop transfer function of a ...
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Calculate input impedance of Common-gate circuit with feedback

The following is from the book Design of Analog CMOS Integrated Circuit, Page 278. The following is used for calculation of input resistance. The book said $$V_{out} = (g_{m1} + g_{mb1}) V_x R_D$$ ...
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Designing a temperature feedback loop in Proteus

I am writing a term paper on the topic "Modeling of an Artificial Blood Circulation Apparatus". The task is to design a control unit based on the ATmega128 microcontroller in Proteus ...
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Why does 'Rfb' affect input impedance?

I am reading "Experimental Methods in RF Design" by Hayward, Campbell, and Larkin published by the ARRL. On the topic of feedback, see that two methods are presented. One method is emitter ...
Yousif Alniemi's user avatar
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Why won't my voltage feedback system work?

Vin is a constant DC source. This circuit will take a random DC input between 12.6V and 48V, and then maintain a constant output voltage of 5V using a system of voltage feedback. with the source code,...
İbrahim İpek's user avatar
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Why isn't feedforward+feedback higher performance than just feedback?

This questions related to feedforward (FF) and feedback (FB) interactions. As an example, say there's a control system keeping a car centered in a lane while driving. Say the car includes a FF sensor (...
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The functionality of a driver circuit

I was requested to make a laser driver circuit for a course project. After some research, I found this circuit. Can someone explain how this circuit works? What is 1R (R5&R6)? Can it be replaced ...
Mu'men Yasser's user avatar
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DC/DC Buck Converter : Implementing Convenient Minor Alterations to Output Voltage

Question How can I perform precision minor output voltage adjustments when using a dc/dc voltage buck converter with high efficiency (including at light loads), without loss of efficiency and without ...
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Calculating the feedback factor of the inverting amplifier?

In the feedback chapater of the Razavi book, he introduces another way to calculate the DC transfer gain of amplifiers in feedback loop. This is given by \$\frac{V_{\mathrm{out}}}{V_{\mathrm{in}}} = \...
Leonhard Euler's user avatar
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Op-amp feedback and stability

I have 2 questions related to this circuit. 1 The first question concerns the open-loop gain. I am tasked with finding both the open-loop and closed-loop gain. The closed-loop gain is calculated ...
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How to determine if the feedback is positive or negative?

How to know if I have to apply the formula Af=A/(1-AB) [positive feedback] or Af=A/(1+AB) [negative feedback]?
Aaryan Pugarja's user avatar
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1 answer
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I don't understand this temperature controller circuit's behaviour [duplicate]

I am trying to build a circuit to regulate temperature for a few microheaters. Here's the circuit I am using: This is a constant temperature controller circuit often found in the research papers and ...
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How can I feed the output of a universal motor (as generator) back into its field coils?

I've been playing around with a universal motor to see if I can get it to generate power - with the aim in mind of trying to connect it to a wind turbine in the future. I have had some success at ...
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Piezoelectric driver circuit

This circuit is used to drive the piezo actuator used in external cavity diode lasers to tune the frequency of the laser. I don't understand the purpose of Op-amp U9 and the other transistors used. ...
Shubham Chowdhury's user avatar
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Contradiction between two circuit simulators in measuring open loop gain

I am implementing what I've learned over the past couple of days. This relates mainly to the simulation of a voltage regulator. I built the (roughly) same circuit in both TINA TI and LTspice to ...
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3 answers
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Why are these voltage regulators seemingly using positive feedback?

Looking over LDO / voltage regulator topologies I keep seeing examples of LDOs where the feedback network is connected to the non-inverting input terminal of the error amplifier. Like this: Taken ...
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Synchronous buck converter using STM32 as feedback controller

I am planning to use stm32f103cbt6 MCU as a feedback controller (voltage or current) for a synchronous buck converter by using gate driver IC, mosfets, inductor, capacitor and etc. Is there any ...
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Measuring flyback SMPS feedback loop response

I'm trying to measure the feedback loop on a isolated flyback SMPS. My goal is to determine the phase margin and 0 dB cross-over frequency. The most common circuit I have seen is the one recommended ...
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How do I explain this regulation action in terms of control theory?

Shown below is a current regulator circuit which ensures an almost constant current through R1 independent of Vin variations. There is no closed loop feedback system evident- How can we explain this ...
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Why will an ideal double integrator oscillator only oscillate at one frequency?

I am trying to learn about RF oscillators. Example 8.6 in the oscillator chapterof RF Microelectronics 2nd edition by Razavi asks to solve for the frequency and amplitude of the oscillation of an ...
VeryItchy's user avatar
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Feedback mechanism intuition

There is a circuit taken from the presentation below. Suppose at some point the VFM voltage rises from V0 to V0 + 0.01 V so V_minus of the op-amp rises too. So what causes the voltage on VFM to return ...
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Is this LDO instability a real problem or a model bug? [closed]

Here is an LTSPICE simulation for which I just have an LDO (ADP7118) in its recommended environment and some reasonable parasitics. It is unstable as you can see in the transient plot (showing the ...
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Non-standard injection point to measure loop stability of SMPS

I have come across this document https://www.ti.com/seclit/ml/slup386/slup386.pdf , where injection points for stability measurement are discussed in Fig.26. For point 3 it says: "Because the op ...
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Problem with the current in a multiphase buck converter

I am a student of electrical and computer engineering and am currently working on a project that involves the study of a multiphase buck converter or synchronous buck converter (2 phases, in my case). ...
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MEMS Oscillator Simulation in LTSPICE

The MEMS oscillator topology i simulate is below fig1: Oscillator schematic Source: A Tunable-Gain Transimpedance Amplifier for CMOS-MEMS Resonators Characterization Below is mine, the resonator i am ...
Jack Huang's user avatar
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How does an SMU change its output impedance from current source mode to voltage source mode?

The above three figures are from the Keithley 237 SMU service manual. From my understanding, the system is configured as a famous two OPAMP precision current-pump topology (shown here). Although I ...
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UCC3895- VS UC3842-based SMPS designs

I have a slight confusion regarding the UCC3895, which is a four-channel wave generator. Earlier I had worked on the UC3842 and therefore to see better results I wanted to take a look at the UCC3895. ...
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UCC3895 based power supply Confusion

I was working on the UCC 3895 IC in order to work on an SMPS design. I've seen the schematics of the IC and I could find any internal reference as done in some other PWM ICs like the UC3842 having ...
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Voltage regulation feedback loops

I have a few questions in my mind. I've searched alot but couldn't find a satisfactory answer. Kindly help me if anyone has knowledge about it. I am concerned regarding the feedback loops of the ...
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UC3842 \$V_{VFB}\$ max rating Vs absolute max rating

I am having a confusion regarding the DC characteristics absolute max rating and the max rating. The absolute max rating tells that beyond this the IC will not work and will be damaged. I am confused ...
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Power Supply Concept; Safety and Completeness - Feedback needed [closed]

I am currently designing a power supply for a circuit I have built. I don’t have a great knowledge about PSUs, everything that I know I have learned in the internet. Unfortunately, my engineering ...
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Need of Cmfb in fully differential amplifiers

Instead of using cmfb circuit to set output dc common mode voltage Why can't we put at dc bais voltage at inverting or non inverting inputs of differential amplifier that way Vocm is set through ...
mahmoud esmail's user avatar
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Feedback and opamp

Consider: Attached schematic is from a broken sampling scope that I have in the lab. Cathode of D1 is connected to a sampling gate output, which is sealed in a metal cage. U5 (top right) is the ...
Emm386's user avatar
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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 ...
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