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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84 views

Why is the closed gain loop -3dB from the open loop gain rather than some other value?

I am reading the book Op Amps for Everyone and in the chapter of feedback loop theory, I have this quote (see picture) where it says in reality the closed loop gain is down by 3dB at the point X as ...
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Books recomendations on certain topics about Op amps and OTA [closed]

Can anyone recommend me some books which the following topics. Related to Op Amps *Positive feedback applications like hysteresis or the next one.... *Non inverting Schmitt Trigger circuit, ...
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1answer
44 views

digital feedback stability

Good evening. i confused to extract the transfer function of the following loop, (shown below) where Cin is a switch cap operated by feedback Fout and Cx switch cap is operated by an external Fref = ...
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117 views

Current feedback and voltage feedback at the same time?

Can I use current negative feedback and voltage negative feedback together to set the operating point of an amplifier?
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63 views

What is the significance of phase margin in an open loop amplifier?

I know the importance of phase margin to ensure stability in closed loop systems, but what about in open loop systems? I am designing a regulated common based LNA IC that operates in open loop. Can we ...
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48 views

Missing information when calculating impedance via Blackman's theorem

The AC course at my university has an ex-exam question where, in the below circuit, the impedance w.r.t. ground has to be calculated for the rightmost node. The question asks to do this using a test ...
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Isolated Type 3 Compensator

I'm trying to build a full bridge dc-dc converter and planning to apply a type 3 compensator(voltage mode). When I check the isolated feedback type 3, I've read some comments indicate that it's hard ...
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2answers
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Confusion in identifying positive/negative feedback of opamp for a given circuit

I was reading this post How are positive and negative feedback of opamps so different? How to analyse a circuit where both are present? for identifying positive/negative feedback of op-amp circuit. ...
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2answers
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Relationship between latency and sampling rate of a digital PID controller

I am trying to set up a fast digital PID controller. The error signal is read by an ADC and sent to an FPGA. The FPGA uses a PID equation to compute the integer sent to the DAC. At the moment I am ...
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3answers
116 views

Simple power amplifier with feedback - designing procedure

I have a problem with understanding the whole feedback business in BJT power amplifier. So far, I only considered it in terms of thermal stability and \$β\$ uncertainty in simple 1-staged amps and was ...
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2answers
65 views

How to safely connect unused opamp stable for gain of +2

Please refer to AD828 or any other bipolar op-amp not unity gain stable. Which of the two below cases is better? Any other suggestion? Simulation suggests the second, but I need to understand if the ...
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Not able to figure out how to solve this as \$I(s)\$ is used in the feedback

I am not able to figure out the approach to this problem because \$I(s)\$ is connected to feedback instead of \$V(s)\$
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Shaftless Hall encoder

Shaftless hall encoder I am building a robot, and one of the stumbling-blocks I found was motor positional control. It seems like the Quadrature encoder is a good choice, but I have no rear axis on ...
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1answer
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Rectifier unit in Neve 33609 Compressor Schematic

Real quick question, I'm analyzing the Neve 33609 schematic (as shown below), and I can't figure out what is responsible for rectifying the AC audio signal into a DC control voltage. If anyone has an ...
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SMPS Control - Comparator in Sinking or Sourcing Configuration

Tried something for fun: I modified a constant-current-output SMPS' feedback-control block which is in sinking configuration to sourcing configuration. Here are the simplified schematics of the ...
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1answer
46 views

Implementing negative feedback on a JFET amplifier

I have started designing and simulating a simple Jfet amplifier using LTSpice. The circuit I have below seems fine, apart from too much gain for my needs (about 20x to much gain). To fix this, I ...
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Why does the feedback mechanism linearize the vi vs vo characteristic curve?

For a unity gain configuration opamp, we arrived at the conclusion that vout = vi * A/(A+1) by using small signal analysis, since A here is the small signal open loop gain. My question is: Why does ...
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2answers
94 views

How is this pole compensated

I have an amplifier in a closed loop, the diagram looks as follows: The DC gain is simple which \$ -Rf/R1 \$. If I make \$ -Rf=2\cdot R1 \$ the the DC gain is two. This is verified using AC analysis ...
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1answer
62 views

How to find Topologies of an amplifier?

How can we find the topology of an amplifier's feedback? I was asked to find the feedback topology of the following circuit, The following observation is made by me: Since the o/p voltage is ...
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1answer
37 views

Stability analysis of cross-coupled amplifier in Cadence

I am trying to implement a cross coupled amplifier with OP-AMP feedback. I am not able to get it stable for a square wave however. The circuit looks as follows: The OP AMP is ideal from Cadence, all ...
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1answer
54 views

What is the controlled variable in this particular case?

I have a question, maybe you can help me because I am not sure of the correct definition. As an example I have a plant with a measured output y in a closed loop system. But as the feedback variable I ...
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41 views

Question about local NFB in a transistor

I've seen this a few times and I can't seem to find documentation so maybe I'm not understanding what's happening here. My interpretation is that the transistor is configured as a common emitter and ...
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1answer
59 views

How adding a capacitor reduces the signal gain to 1 in an op-amp?

Here I can't understand how adding a capacitor reduces the signal gain to 1?
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1answer
85 views

TL431 vs. SMPS transient response

I am currently working with few 150 W SMPS designs for industial applications with heavy transient load condition. Current design works well by mean of line/load regulation and device reliability but ...
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1answer
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How do I combine outputs in Simulink by changing a specific parameter?

I am studying a Cruise control system, and I want to change the coefficient of rolling friction and put them together in one graph keeping the remaining parameters the same. How do I store all the ...
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2answers
64 views

Problem in controlling the device temperature using an op-amp

OBJECTIVE: I have a device to which voltage is applied and this voltage has to be controlled according to the temperature detected by the thermistor that is placed on the device. If the temperature of ...
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1answer
57 views

Gain with load or gain without load?

There is a problem I have been dealing with for hours. In my Electronic 1 lecture, small signal analysis was like this: The small signal equivalent of this circuit in my lecture notes was this: When ...
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1answer
62 views

How to prevent algebraic loop in the control loop simulation?

I have been developing a simulation of the field oriented control of the three phase induction motor. The simulation is developed in the Scilab/Xcos (v5.5.2) which is a free of charge Matlab/Simulink ...
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1answer
36 views

Appropriate resistor values for 5V LNK low-power supply in CC mode

UPDATE: QUESTION SOLVED/CLARIFIED. PLEASE REFER TO THE LAST "HAND MADE" SCHEMATIC IN THE SERIES OF PICTURES BELOW, AND READ MY FINAL "SOLUTION". Original question: * I wonder what ...
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1answer
92 views

Analysing BJT circuit

Recently, I found this circuit on the Talking Electronics web page: I was interested in the modified circuit below, where the feedback capacitor is replaced with short circuit and the 8R speaker with ...
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3answers
358 views

How does the compensation resistor in an inverting amplifier compensate for the input bias current?

I can't see how a resistor placed on a whole other input terminal has anything to do with compensating this input bias. i.e. the input stages are just the gates of transistors of differential stage. ...
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1answer
59 views

Why doesn't the negative feedback current in an op-amp inverting amplifier drive the op amp into saturation?

I know the rule that states that the negative feedback will keep the difference in potential between the inverting input and the non-inverting input (almost) zero. Now I just wanted to take a moment ...
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2answers
103 views

Is this voltage division equation correct?

I am trying to study the significance of resister divider feedback circuit in buck regulator. This is the TI document I am referring to. As per TI doc, voltage at the feedback pin is as follows, When ...
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2answers
93 views

Effect of parameters on feedback system and some confusion regarding it

I am confused in some basic terminologies of feedback system and its requirements 1.what is difference between actual input ,reference input and disturbance input ? 2.is reference input setup by ...
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3answers
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Location of input for negative feeback bandpass filter

I came across a reference design on a TI application imaged here: It is clear to me that there is a bandpass filter on the negative loopback branch of the amplier. However, from the few electronics ...
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1answer
53 views

What is the R-C Feedback to this FET?

I'm studying this RF Power Amplifier and I'm curious about the drain-gate feedback shown as R3 and C6: What is the purpose of the R-C feedback? What is this mechanism known as?
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1answer
92 views

Would a suitably placed inductor stop audio feedback whine?

To give some context, I am designing a cosplay armor costume that somewhat muffles everything that is spoken while wearing it. I have a simple low power audio amp that I was intending to use to ...
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2answers
90 views

Op-Amp Comparator Testing

I am having this op-amp Comparator. My circuit is similar to this circuit present in the datasheet of the IC, page 21. I have this circuit now in my board which I want to test. I have never tested an ...
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1answer
65 views

I need help deriving the cutoff frequency of a negative feedback amplifier

I have the question and answer below for deriving the closed-loop cutoff frequency of a feedback amplifier circuit. I can follow the working out all the way until the last 2 lines, where the writer ...
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0answers
94 views

Gain error calculation for op-amp circuit in inverting configuration

For an inverting op-amp, calculate minimum gain that is required for the op-amp to achieve a gain error of 1%, if the required closed-loop DC gain is -9. If the input resistance R1 is 1Kohm,find the ...
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2answers
702 views

Where do zeroes come from in a circuit?

I'm having difficulty fully understanding how exactly a zero is created in a circuit. I would like some way of visually recognizing (without computing a transfer function) that a zero will be present, ...
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3answers
73 views

What is the definition of “the loading of feedback network on the input/output side”?

There is the following example: simulate this circuit – Schematic created using CircuitLab Its loading of the feedback network on the input side is 40kohm in series. Its loading of feedback ...
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1answer
54 views

Closed-loop pole moving to RHP - less stable or more stable?

I was reading Razavi's Design of Analog CMOS ICs book and came across this in the Stability and Freq. Compensation chapter, What the book says The closed-loop transfer function of a system is given by ...
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9answers
2k views

How does negative feedback change output impedance?

Hi, I'm having some trouble intuitively understanding how negative feedback changes output impedance. I was always taught that negative feedback changes the gain of a circuit - from A_OL to (A_OL)/(1+...
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'Weaker' feedback reduces DC Gain?

My Understanding From my previous understanding of stability and op-amps, I know that placing an op-amp in a closed-loop configuration reduces the DC gain and extends the 3-dB bandwidth as seen in the ...
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103 views

PT2399 delay chip feedback issue

I'm facing a strange issue which I can not identify. The circuit is the basic PT2399-based echo. My components setup is based on the research of similar circuits: The problem is that I'm not getting ...
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1answer
66 views

How does this DC Electric Motor Control Circuit Works

I'm trying to figure out how does this DC motor controller circuit works. The circuit originally controls 2 DC motors for lifting a table. I extracted section relating to one motor only. I added my ...
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4answers
187 views

How to determine if the feedback is positive or negative in this circuit?

Is the feedback in this circuit positive or negative? How can I know?
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83 views

Middlebrook's Method VS Tian's Method VS Middlebrook's General Feedback Theorem

For https://sites.google.com/site/frankwiedmann/loopgain , how is Tian's Method different compared to Middlebrook's Method and Middlebrook's General Feedback Theorem ? Tian's Method Middlebrook's ...
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1answer
69 views

Capacitor ESR Calculation

I'm trying to perform esr calculations of this capacitor(1uF): https://alconelectronics.com/wp-content/uploads/2020/06/KP-6-JUNE-2019.pdf to do that I need to know dissipation factor and at the bottom ...

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