Questions tagged [positive-feedback]

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Unstability condition for positive feedback network involving phase change

For positive feedback: \$G=\frac{A}{1-AB}\$ According to Wikipedia, this system is unstable for AB>1. This condition appears to be for the cases when 'A' and 'B' have real values. But in general, A ...
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2answers
93 views

Op-amp circuit to control gain of two analog channels with one single-section potentiometer

I'm working on designing my own headphone amplifier with extremely high fidelity. One thing I want to incorporate is a circuit to control the gains of the two channel's using one single-channel ...
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1answer
56 views

What is topology of feedback for circuit?

I am confused between Voltage Shunt and Current Shunt Also mention why R2 shouldn't be considered as feedback as it is emitter degeneration resistance Consider the above circuit why can't I consider ...
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1answer
35 views

How do I find this value for the feedback fraction?

How exactly do I find this value for the feedback fraction Beta? Thank you. omega_0 here is the natural frequency calculated as omega_0 = 1/RC and s is the complex frequency.
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193 views

Offset voltage comes to saturation in coupling amplifier circuit using OpAmp with Gain=100

I did get in troubles with my student project circuit below! The purpose is to amplify difference between two inputs. Specifically, 20mV and 10mV are connected with input to get 1V at the last OpAmp'...
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3answers
161 views

Why the Wien Oscillator output is a sine?

I don't understand why the output signal of the Wien oscillator is a sinusoidal waveform. I can easily understand how a sine waveform can be generated by an oscillator which contains an LC circuit (...
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1answer
56 views

Can oscillations happen even if negative feedback is present?

By OPAMP book says that virtual short is applicable in OPAMP only if negative feedback is present an output is not oscillating.I don't get how oscillations can occur at output if the feedback is ...
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2answers
89 views

Can negative feedback in OPAMP be applied at not inverting terminal?

In figure 1 is the feedback regenerative in nature and if yes can I apply virtual short to solve it.
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2answers
103 views

How to identify the circuit has negative feedback or positive feedback?

I am having difficulty in identifying whether feedback is negative or positive (i'm not talking about feedback topology) My teacher told that there is a method in which, after deactivating ...
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1answer
70 views

Misconception in opamp feedback

Is it a misconception that feedback into inverting terminal of opamp is negative feedback and feedback into noninverting terminal will be positive feedback? I feel it is. Because all oscillators have ...
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3answers
88 views

Negative feedback sustainability

If positive feedback makes output exponentially increase and cause instability in an opamp then why doesn't negative feedback make output extremely small and cause the system to collapse?
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1k views

Can someone explain this op amp “tone control”?

Its supposed to be part of a guitar effect pedal, why is there positive feedback besides the negative feedback? I was reading about op amps and from what i understand positive feedback is very rarely ...
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4answers
314 views

Voltage buffer with ideal Op-Amp (positive feedback) - Instability

I know that the circuits which employ negative feedback are stable, whereas those which employ positive feedback are not stable. How can I prove that a voltage buffer (ideal op-amp) which uses ...
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1answer
330 views

Determining The Polarity of a FeedBack Circuit

In determining the polarity of such a circuit I used the following reasoning: if Vin goes up ID1 goes up and ID2 goes down, ID4 goes down and VG3,VG4 go up because of PMOS, then Vout goes down, if ...
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834 views

Determine if feedback is negative or positive?

Is there a way to know from how a circuit is designed that is has negative feedback or positive feedback. Here are some examples: Example 1: Example 2:
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3answers
1k views

Confusion about positive feedback condition in gain equation

Closed loop gain A' of the above op amp system is given as: A' = A / (1 + β*A) where A is the open loop gain which is a positive huge number. Here as a side note, my understanding is that β being ...
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2answers
448 views

Feedback factor of Armstrong Oscillator

I am trying to find an equation for the feedback factor of an Armstrong oscillator in terms of the transformer inductances and I can't find one in books. Am I correct if I say that the feedback ...
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1answer
414 views

What if you alter a differential amplifier by giving it a positive feedback rather than a negative feedback?

Figure 1 In the above Image 1, you see is a differential amplifier . It has a negative feedback as required. Now take a look at figure 2 below. Figure 2 Lets take a look at figure 2. Now that I ...
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1answer
354 views

What's the purpose of the 'positive feedback resistor' in the circuit

There is a 1M Ohms 'positive feedback resistor' in the 10mA current source below: What's the purpose of it? Update: Some people just think it's not a 'feedback' but simply a resistor tied to ground,...
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2answers
651 views

How to justify that op-amp 1 has negative feedback?

Op-amp 1 is topmost in the schematic below. I used the ideal amplifier method (using A until the end and then lim A->infinity) and also the virtual short method. But I don't know if that's enough to ...