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95.1.4. General Principle
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Today, we're going to explore how feedback affects the frequency response of amplifiers. Can anyone tell me what they understand by feedback in circuits?
I believe feedback is when some of the output is sent back to the input to control and stabilize the system.
Exactly! Feedback can help in stabilizing and improving the performance of amplifiers. Now, how does it affect the frequency response?
Doesn't it change the gain of the amplifier?
Yes, it does! The gain of the amplifier can be expressed as a function of frequency, and feedback modifies this. Remember the acronym GAF: Gain Affected by Feedback.
Got it! But how does feedback affect pole positions?
Great question! That's what we'll discuss next. Feedback can shift the poles' locations in the feedback network, affecting both gain and stability.
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Let's focus on poles in our feedback systems. Can anyone explain what a pole is in this context?
A pole in this context is a frequency where the output of the circuit significantly changes or drops.
Exactly! The position of these poles affects the stability and the responsiveness of the amplifier. We often calculate the new pole location when feedback is applied.
And how do we determine that new pole?
Good question! The new pole can typically be expressed as a function of the original pole and a factor related to feedback, like (1 + βA).
How do we visualize this effect?
That's where Bode plots come into play! They help us visualize gain and phase across frequencies.
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Create a free accountNow, let's discuss positive and negative feedback. Who can tell me how they differ in terms of stability?
Negative feedback usually stabilizes the system while positive feedback can lead to instability.
Correct! Negative feedback reduces gain but improves frequency response. Remember: NFG– Negative Feedback Gains Stability.
What happens if we have multiple poles in our feedback system?
Great point! Multiple poles can complicate the analysis, but we can still analyze them through approximations.
Are we also considering the feedback's impact on bandwidth?
Absolutely! The gain-bandwidth product is a crucial metric to maintain while adjusting the feedback.
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Create a free accountLet's apply what we've learned through a case study. Suppose we have an amplifier with one pole. How would feedback change its frequency response?
We would see the pole location shifting, probably at a lower frequency due to the feedback.
Exactly! And if we had two poles, how would we approach that?
We need to consider the relationships between the poles and might use approximations based on frequency.
Perfect! And it's essential to remember that the gain-bandwidth product remains a valuable constant in these scenarios.
I'm feeling more confident about these concepts. Thanks!
You're welcome! Let’s summarize: Understanding poles, feedback type, and bandwidth gives us powerful tools in circuit design.
Overview
Short Summary
This section explores the effect of feedback on the frequency response of amplifiers, focusing on pole locations and their implications.
Medium Summary
In this section, we delve into how feedback networks influence the frequency response of amplifiers in analog electronic circuits. Key concepts include the behavior of pole locations within feedback systems, the impact of feedback on amplifier gain, and the relationship between loop gain and stability of the system.
Detailed Summary
General Principle - Detailed Summary
In this section, we discuss the effect of feedback on the frequency response of forward amplifiers and their associated feedback networks. Feedback systems are vital in ensuring amplifiers function stably and predictably. We focus on how feedback can alter the location of poles in the feedback system, which in turn impacts gain and overall performance.
The discussion covers the scenarios of amplifiers with different numbers of poles, analyzing one-pole and two-pole systems. The significance of loop gain is examined, highlighting how it defines the relationship between the output and input signals when the signal returns through feedback.
Key points include:
- The definition of frequency response concerning amplifier gain and stability.
- The influence of feedback networks on the positions of poles and the resulting system stability.
- The conclusion that the gain bandwidth product remains constant despite shifts in pole locations due to feedback.
Overall, understanding these principles is essential for designing effective analog electronic circuits, as it helps predict how amplifiers will behave under various conditions.
Reference YouTube Videos
Audio Book
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Create a free accountIn general, we can say that it is valid for even other linear circuit, but our specific focus it will be on the amplifier. And also when you say frequency response, it is primarily our focus it will be on the gain of the amplifier, but that is also applicable for impedance. In fact, that is applicable for with other gains also current gain, transconductance, transimpedance and so on. So, our discussion today it is relatively generic and we will see that how the frequency response changes due to the presence of feedback circuit.
Detailed Explanation
This chunk introduces the concept of frequency response in amplifiers and linear circuits. Frequency response describes how an amplifier's gain, or output signal strength, varies with different frequencies of input signals. It is not only relevant for gain but is also crucial for understanding how amplifiers and other circuits behave in terms of impedance and different types of gains (current gain, transconductance, etc.). The primary focus of the discussion is to examine specific examples of how feedback from the circuit affects these frequency responses.
Examples & Analogies
Think of an amplifier as a speaker that can play music at different volumes depending on the music's pitch. Just like the speaker's responsiveness can change based on the frequency of the notes played (some may sound better at high volumes while others may not), the amplifier's frequency response indicates how well it can amplify signals at different frequencies. The feedback circuit acts like a sound engineer who tweaks the speaker settings based on the type of music being played.
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Create a free accountThe concepts we will be covering today it is primarily how the locations of the poles are getting changed, in the feedback system and that is due to the location of the amplifier's poles and also the poles of the feedback network. We shall focus on the situation where the amplifier may be having one pole or maybe it is having two poles or maybe three poles. And also, we will be considering cases where the feedback network may not be having any pole only the amplifier maybe having pole or maybe the amplifier and as well as the feedback network may be having poles.
Detailed Explanation
This chunk discusses how the feedback system affects the poles (specific frequencies where the gain of the amplifier significantly drops or changes) in frequency response. The pole locations in an amplifier determine how the amplifier behaves at different frequencies. Changes in feedback can shift these poles, influencing the overall performance of the amplifier. Importantly, the lecture will cover scenarios with different numbers of poles, including cases where either the amplifier or the feedback network introduces poles or both do.
Examples & Analogies
Imagine a seesaw that balances differently depending on where the weight is placed (like poles in a circuit). If the weight is closer to the center (representing the original pole), the seesaw is stable, but if the weight shifts to one side (the effect of feedback), the balance point (or pole) shifts, changing how the seesaw reacts. In this analogy, a feedback system is like someone adding or removing weight from different parts of the seesaw to help achieve a better balance or response.
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Create a free accountSo, we recapitulate what we have discussed. In fact, we have discussed this kind of situation where this is the forward amplifier, this is the feedback network, and then we do have signal mixture and then we do have signal sampler. And the forward amplifier gain it is A and the primary input to primary output gain we call feedback system gain A. As we know that this feedback system gain it is f.
Detailed Explanation
In this chunk, the discussion is about understanding how feedback systems are structured, including the components comparison between forward amplifier and feedback network. The gain of the forward amplifier is noted as 'A', while the combination of this amplifier with the feedback network creates a more complex system gain, denoted as 'A_f'. This concept is essential as it leads to understanding the overall effect of feedback on the amplifier gain in both time and frequency domains.
Examples & Analogies
Consider a conductor orchestrating an orchestra. The conductor (the amplifier) sets the pace and volume of the music (output). The musicians (the feedback network) adjust their sounds in response to the conductor's cues, enhancing or altering the music (combined gain). This collaboration formulates the overall quality of the performance, much like how feedback modifies the amplifier's output based on the input signal characteristics.
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Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Feedback Impact: Feedback significantly alters the gain and stability of amplifiers.
Poles and Stability: The location of poles in the feedback system determines the stability and frequency response.
PaswB: Gain and Bandwidth Product remains constant across feedback changes.
Examples
Step-by-step examples to apply the section's ideas and test your understanding.
An example of an amplifier with a single pole where feedback shifts the pole's location can be represented graphically using a Bode plot.
In a two-pole system, the interaction between each pole can illustrate how feedback modifies frequency response and overall gain.
Memory Aids
Interactive tools to help you remember key concepts
Stories
Flash Cards
Glossary
Feedback
The process of routing a portion of the output signal back to the input to enhance stability and performance.
Pole
A frequency at which the transfer function of a system becomes infinite, significantly impacting the system's output.
Loop Gain
The product of the forward amplifier gain and feedback network gain, which helps assess stability in feedback loops.
GainBandwidth Product
A constant for amplifiers, representing the product of gain and bandwidth, useful for designing amplifiers.
Bode Plot
A graphical representation of the frequency response of a system, showing gain and phase shift across frequencies.