Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [loop-gain]

85 questions
11
votes
3 answers

What is the best way to simulate the open-loop gain of an op-amp in LTspice?

I have been trying to simulate open-loop gain to check the SPICE model in LTspice. From what I could find out so far, there appear to be two main approaches to achieve this. The example in this video breaks the feedback path to the inverting pin…
kenearl
  • 115
  • 7
6
votes
2 answers

Loop gain(s) for multi-loop circuits

With the aim to combine some good properties of two different opamp types we can make use of the composite amplifier principle (see the figure). For example, we could combine good (small) input offset parameters (amplifier OP1) with good (large)…
LvW
  • 24,857
  • 2
  • 23
  • 52
5
votes
2 answers

Instability of fully differential op-amp in LTspice

I tested the following circuit including a fully differential op-amp for stability in LTspice. The circuit has an inverting gain of 6 and a roll-off at 4 MHz. When exciting the circuit with a step, the op-amp starts oscillating. Circuit for time…
FrüchteTony
  • 109
  • 5
5
votes
2 answers

What's the largest practical stable gain possible?

I have a feedback application to set the voltage of a node in which there is considerable loss in the loop. Simulations tell me that a differential voltage gain of 10000, 80dB (roughly about what you normally get from a single open-loop opamp) is…
Edgar Brown
  • 8,336
  • 2
  • 16
  • 53
5
votes
3 answers

Understanding the negative feedback and stablizing of a current limiter

Here's a current limiter circuit that uses the negative feedback to limit the current to a certain point. simulate this circuit – Schematic created using CircuitLab I have not studied feedback systems before as I'm not an EE student just do it for…
dirac16
  • 1,774
  • 2
  • 12
  • 17
4
votes
3 answers

Frequency analyzer for loop gain measurement - Why should the injection point have low output impedance and high input impedance?

@5:08 The video mentions: "The insertion point should have a low output impedance and high input impedance" What is the background for this condition?
Divya K.S
  • 2,489
  • 16
  • 31
4
votes
6 answers

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\$ (just to give a very simple example), I just see that…
Tendero
  • 1,010
  • 1
  • 12
  • 25
3
votes
3 answers

Why can you define closed loop gain when return ratio approaches infinity like this?

This is from this lecture video. Please check the video link if you're not familiar with the terms. I can explain it but I think the video lecture is pretty good at it. Because the feedback amplifier is linear, signals \$s_{ic}\$ and \$s_{out}\$…
emnha
  • 1,547
  • 4
  • 34
  • 84
3
votes
4 answers

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 network on the output side is 2kohm in parallel. There is…
Audra Jacot
  • 33
  • 4
3
votes
4 answers

Differential Amplifier's Unusual Behavior

This circuit is made of one differential BJT transistor pair and voltage-amplification stage with negative feedback. simulate this circuit – Schematic created using CircuitLab About this circuit for DC conditions. Current through current source…
Keno
  • 2,360
  • 2
  • 35
  • 65
2
votes
1 answer

Open-loop frequency response for an op-amp

I want to know what is the ideal circuit to measure open-loop frequency response and why?I have seen the typical open-loop frequency response curve for an op-amp a lot of times. But when I try to plot it for my circuit simulation even though it…
vikas sajanani
  • 41
  • 6
2
votes
1 answer

Calculating the loop gain for an ideal op-amp with time delay

In the circuit below, \$\tau \$ represents a time delay. We are using a first-order Pade approximation for this time delay. This means that \$\ e^{-s\tau} = (1-s\tau)/(1+s\tau)\$. Below is the circuit. Does the feedback term, \$\ B = R + …
Hector
  • 341
  • 3
  • 15
2
votes
0 answers

Why gain crossover frequency must be lower than phase crossover frequency for stable systems?

As far as I understood from here, phase margin means the amount of phase that needs to be added in order to coincide with 0 db gain and -180 degrees phase. Likewise for the gain margin it means means the amount of gain that needs to be added in…
aadil095
  • 233
  • 2
  • 9
2
votes
2 answers

calculate feedback factor in feedback circuit

Below is an exercise with solution about feedback network. I am wondering how the feedback factor is calculated like that. Could anyone shed some light on this?
emnha
  • 1,547
  • 4
  • 34
  • 84
2
votes
3 answers

Series-Shunt Feedback Amplifier Analysis - Finding Loop Gain

So I'm trying to solve a problem I found in a textbook (won't say which one so people can't use it to cheat on their hw) and I haven't been able to arrive at the answer found in the appendix. Please note this is not a homework problem, I graduated…
Alexander Villa
  • 107
  • 11
1
2 3 4 5 6