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Welcome, everyone! Today we're discussing how feedback networks affect the frequency response of amplifiers. Can anyone tell me what a feedback network is?
Isn't it a circuit that takes some of the output signal and feeds it back to the input?
Exactly! And this feedback can be positive or negative. In our case, we'll focus on negative feedback, which helps in stabilizing gain and improving bandwidth. But how do you think it influences the gain and phase?
I think it modifies the gain at different frequencies?
That's right! We will see how the gain changes due to the poles created by the amplifier and the feedback network. The poles dictate the frequency response.
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Now let's examine a situation where our amplifier has only one pole. What can you tell me about the effect of feedback on this pole?
The feedback will shift the pole, right?
Precisely! The new pole location, pβ, can be described as a function of the original pole p and the feedback gain. It's important for us to visualize this shift on a Bode plot. Has anyone seen a Bode plot before?
Yes! It shows gain in dB over a log scale of frequency.
Exactly! Understanding these plots will help us visualize the gain and phase relationships in feedback systems.
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Now let's expand our discussion. What happens when our amplifier has two poles instead of one?
I think the interactions get complex, right? The feedback might affect more than one pole.
Correct! The feedback not only shifts one pole but could also influence the second pole. If one pole is prominent, the feedback primarily shifts that pole's behavior. What might this mean for the system's overall behavior in the frequency response?
It might create bandpass characteristics where certain frequencies are amplified more than others?
Exactly! This is essential to understand for designing circuits that behave well over the intended frequency ranges.
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The section elaborates on how feedback networks alter the frequency response of amplifiers, emphasizing the shift in pole locations and gain characteristics. It also covers both one-pole and two-pole systems under negative feedback conditions.
In this section, we explore the effects of feedback networks on the frequency response of amplifiers. As feedback alters the behavior of amplifiers, it plays a crucial role in determining the gain and phase characteristics of the system.
Feedback mechanisms can significantly influence how amplifiers respond to different frequencies. The discussion focuses on how the locations of polesβcritical points in the frequency responseβshift due to feedback. By examining single and multiple pole scenarios, the section delves into how gain varies with frequency in the presence of feedback.
The key takeaway is the relationship between the feedback loop gain and pole shifts in frequency response. A deeper understanding of this subject allows learners to predict system behavior and optimize circuit designs effectively. The chapter emphasizes the importance of analyzing amplifiers in the Laplace domain for a robust understanding of their frequency response dynamics.
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From this frequency onwards this part it is getting very small. So, if I ignore this part compared to 1, then what I have it is A = A(s) = = A(jΟ).
In this part, the speaker is explaining the concept of how the gain of a feedback system behaves beyond a certain frequency. They indicate that as frequency increases, the contributions from certain components of the gain equation become negligible compared to 1. Hence, they simplify the gain equation to focus only on the dominating term.
Think of it like focusing on the loudest sound in a crowded room. As the background noise (higher frequencies in this context) increases, you can start ignoring some of the softer whispers because they don't contribute much to what you hear as dominant. Similarly, in the gain equation, beyond a certain frequency, some factors can be ignored.
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So, if I consider the plot for say to start with let you consider A. So, A is having a low frequency gain A of course, it is converted into decibel dB and then it is having a pole and beyond that it is having a role of like this.
The plot of gain indicates how the gain of an amplifier behaves over a range of frequencies. Initially, at low frequencies, the gain is at its nominal value (A). As the frequency approaches a pole (where gain starts dropping), the curve starts dropping significantly, demonstrating how gain is affected by frequency. This drop is crucial because it indicates the frequency response of the amplifier, which helps in understanding how well an amplifier will perform in different applications.
Imagine a water slide. At the top, you have a smooth and steep slide where the water flows quickly (high gain). However, as you go down the slide, certain bumps (the pole) cause the water to splatter and slow down (lower gain). Therefore, understanding where the slide starts to flatten (the pole) can help you figure out how fast you will go down.
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If I sketch the loop gain here, so Ξ² < 1. So, we are assuming this is Ξ² < 1 which means, that it is having the same pole and then it is having role of 20 dB/dec.
Loop gain (AΞ²) is discussed in conjunction with the feedback system. When the feedback factor (Ξ²) is less than 1, it denotes a scenario where the system is stable and the gain reduces gradually. This gradual change can be plotted as a line that showcases a 20 dB per decade drop. Understanding loop gain is crucial as it helps in analyzing how feedback influences the overall performance of the amplifier across varying frequencies.
Consider driving a car on a gradually inclined road (the loop gain), where you need to accelerate more to maintain your speed. If you initially have a good speed (high gain) but the incline gets steeper (frequency increases), you might need to adjust how much you accelerate (loop gain) to maintain your speed. Similarly, when feedback is applied, the loop gain must be considered for the amplifier's proper functioning.
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So, the conclusion here it is in the next slide it is what just now we said it is yeah. So, we do have this A and this is what the approximation we do have.
This segment summarizes the importance of understanding gain and phase in feedback systems. It suggests that the approximations made help in simplifying complex feedback interactions and makes it easier to predict amplifier behavior under different conditions by focusing primarily on the dominant features of the frequency response.
It is similar to tuning a guitar. When tuning, you focus on the most prominent notes first to get the right sound, ignoring the minor fluctuations of other strings until you have a clear base tune. Similarly, in analyzing gain and phase, focusing on significant factors allows for better control and understanding of overall system behavior without getting lost in complex variables.
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Key Concepts
Feedback Network: A system that influences amplifier gain and stability.
Pole Location: Determines gain drop-off and frequency response shape.
Bode Plot: A representation of gain and phase that helps visualize the response.
Loop Gain: A crucial factor in assessing stability and performance in feedback systems.
Negative Feedback: Improves stability and bandwidth by reducing the gain at certain frequencies.
See how the concepts apply in real-world scenarios to understand their practical implications.
In a simple audio amplifier, negative feedback may reduce distortion, enhancing the clarity of sound output.
When designing a control system, one might use Bode plots to optimize system response and stability using multiple poles.
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Gain and phase play a vital role, feedback shifts the pole.
Imagine a conductor leading a band. The musicians adjust their tempo based on the conductorβs cues, just like how feedback adjusts amplifier response.
Remember β G.P.F. (Gain, Phase, Feedback) β Key elements in analyzing frequency response!
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Review the Definitions for terms.
Term: Feedback Network
Definition:
A circuit component that feeds part of the output signal back to the input to control the amplifier behavior.
Term: Pole
Definition:
A frequency at which the gain of the system drops significantly, affecting the overall frequency response.
Term: Bode Plot
Definition:
A graphical method for displaying the frequency response of a system, showing gain and phase across frequencies.
Term: Loop Gain
Definition:
The product of the forward gain and feedback gain, used in determining stability and gain characteristics.
Term: Negative Feedback
Definition:
A feedback system where the output is fed back in a manner that oppositely affects the input, stabilizing the system.