90.1 - Feedback System (Part–A)
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Introduction to Feedback Systems
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Welcome students! Today, we’re going to discuss feedback systems. It's important to understand how feedback can influence the performance of amplifiers.
Can you explain what a feedback system is?
A feedback system involves sending a part of the output signal back to the input of the amplifier. This can help stabilize the circuit or modify its response.
What's the difference between feedback and no feedback?
Without feedback, the amplifier operates with a fixed gain, potentially leading to distortion. Feedback helps to control sensitivity and improve linearity.
Can we actually see how feedback affects the amplifier?
Indeed! We'll compare performance with and without feedback as we progress.
Can you summarize the key points we've discussed?
Certainly! Feedback systems bring a part of the output back to the input, affecting stability and response. Next, we'll look deeper into types of feedback.
Types of Feedback Systems
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Now let’s dive into the types of feedback systems. We generally have two types: negative feedback and positive feedback.
What is negative feedback?
Negative feedback takes the output that counteracts changes in the input, aiming for stability. It reduces gain sensitivity.
And what about positive feedback?
Positive feedback, on the other hand, amplifies changes at the input, which can lead to instability. It's useful in oscillators.
Is that why we see oscillation in some systems?
Exactly! We'll explore how different configurations affect this behavior as we continue.
Can you recap the differences?
Of course! Negative feedback stabilizes and controls gain, while positive feedback amplifies and can cause oscillation. Let's examine their practical implications next.
Transfer Characteristics
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We've established feedback types; now, let’s discuss transfer characteristics. Why are they important?
I think they help us understand gain, right?
Exactly! The input-to-output transfer characteristic of a feedback system defines how the output responds to the input. It's crucial for assessing performance.
Can we derive this mathematically?
Yes! We'll use equations to illustrate how feedback modifies gain. This leads us to the desensitivity factor.
What is that factor exactly?
The desensitivity factor indicates how feedback enhances stability and alters gain, which is fundamentally defined based on loop gain.
Can you summarize the insights we've gained about feedback effects?
Certainly! Transfer characteristics and desensitivity are pivotal in feedback systems. They inform us about control over gain stability. Next, let’s engage with some practical examples.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
The feedback system is a critical aspect of amplifiers in analog electronic circuits, where a portion of the output signal is fed back to the input. This section delves into the basic theory of feedback systems, identifies two primary types—negative and positive feedback—and describes how these influence amplifier performance through different configurations.
Detailed
Feedback Systems in Analog Electronic Circuits
In this section, we explore the foundational concepts of feedback systems as applied in analog electronic circuits, beginning with the basic feedback theory and moving towards specific configurations. Feedback systems are defined as those which take an output signal and return a portion of it to the input, thus altering the input signal used by an amplifier.
Key Concepts Covered:
- Basic Model: The feedback system includes a forward amplifier transmitting signals and a feedback path sending part of the output back to the input. The forward gain is denoted as 'A' and the feedback factor as 'β'.
- Types of Feedback: Two main types are discussed:
- Negative Feedback: Where the feedback signal counteracts the input signal, stabilizing the system and reducing gain sensitivity.
- Positive Feedback: Here, the feedback signal enhances the input signal, potentially leading to instability or oscillation.
- Transfer Characteristics: The derivation of the input-to-output transfer characteristics reveals how feedback affects amplifier gain, particularly highlighting the desensitivity factor, which addresses changes in gain due to feedback incorporation.
Significance:
Understanding feedback systems is essential for designing reliable and effective analog circuits, as they impact stability, gain, and performance significantly.
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Introduction to Feedback System
Chapter 1 of 10
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Chapter Content
So, students welcome back to our online certification course on Analog Electronic Circuits. Myself Pradip Mandal from E and EC department of IIT, Kharagpur. Today’s topic of discussion it is Feedback System. So, we shall start with basics and then gradually, we will be moving to practical circuit.
Detailed Explanation
In this introduction, the instructor welcomes students and introduces the topic of feedback systems in analog electronic circuits. This sets the stage for learning, emphasizing that the session will begin with fundamental concepts before advancing to practical applications.
Examples & Analogies
Think of a feedback system like a coach in a sports team. The coach observes the players' performance, gives them constructive feedback to improve, and guides them on how to enhance their skills during practice. Similarly, feedback systems analyze outputs to adjust inputs for better performance.
Overview of Course Structure
Chapter 2 of 10
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Chapter Content
So, the based on our plan overall plan, we are in modules in fact, whatever the concepts we will be talking it is primarily on analog modules and today we are starting this week-10. In fact, it is module-9 and as I said that we are going to talk about feedback system.
Detailed Explanation
Here, the instructor informs students about the course layout, clarifying that the material is organized into modules focused on analog systems. The current discussion falls within the 10th week of the course, specifically module 9, and is centered on feedback systems.
Examples & Analogies
If you think of a textbook as a road map, each module represents a different route. Following the modules systematically allows students to journey through the world of analog systems, ensuring they explore various important topics without getting lost.
Basic Concepts of Feedback System
Chapter 3 of 10
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Chapter Content
To start with the basic concept of feedback system so, far we are talking about amplifiers. In fact, different amplifier configurations and those amplifiers are essentially linear circuit.
Detailed Explanation
The instructor begins discussing the foundational concept of feedback systems, particularly in relation to amplifiers. These amplifiers are described as linear circuits, meaning their output is directly proportional to their input, which is crucial for understanding how feedback influences their behavior.
Examples & Analogies
Imagine a dimmer switch for lights; when you increase the input (turning the knob), the brightness of the light increases proportionally. In this way, amplifiers function similarly—adjusting inputs to control outputs smoothly.
The Feedback Structure
Chapter 4 of 10
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Chapter Content
Whenever you are talking about the feedback system, what we are trying to do, we are essentially sampling this signal and part of it we are taking back and we are given to the input.
Detailed Explanation
In feedback systems, a portion of the output signal is 'sampled' and returned to the input. This process allows the system to adjust its operation based on the output behavior. The structure combines the sampled output (feedback signal) with the original input to optimize system performance.
Examples & Analogies
Consider a thermostat that regulates room temperature. It measures the current temperature (output) and, if too warm, adjusts its control to cool down (input). The thermostat samples the temperature and modifies its behavior based on what's measured.
Types of Feedback Systems
Chapter 5 of 10
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Chapter Content
And we shall talk about types of feedback systems, basic types of feedback system and then we shall derive transfer characteristic of feedback system.
Detailed Explanation
The instructor notes that the session will cover different types of feedback systems, including negative and positive feedback. Additionally, the concept of transfer characteristics, which describe how changes in input affect output, will be derived and explained.
Examples & Analogies
You can think of gaining feedback as adjusting the volume on your sound system. If you increase the volume (input), the system's output enhances in response (i.e., the sound gets louder). Positive feedback keeps amplifying, while negative feedback helps balance sound to prevent distortion.
Forward Amplifier and Feedback Paths
Chapter 6 of 10
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Chapter Content
So, if you see this in this feedback system what are the basic modules we do have first of all we do have forward amplifier. So, this is called forward amplifier which is taking the signal from left to right and then we also have feedback path.
Detailed Explanation
In a feedback system, there are two primary components: the forward amplifier, which processes signal flow from input to output, and the feedback path, which takes part of the output signal back to influence the input. Understanding these modules is essential for analyzing how feedback control works.
Examples & Analogies
Think of a feedback loop like a conversation where one person speaks (forward amplifier) and the other listens and responds (feedback path). The listener's response helps refine the speaker's message for clarity, just like feedback helps adjust the output of an amplifier.
Negative and Positive Feedback
Chapter 7 of 10
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So, we can say that this mixer predominantly it is not amplifying or attenuating, it is rather either multiplying with + 1 or ‒ 1 and then combining the primary input signal and the feedback signal to generate the input signal for the amplifier.
Detailed Explanation
Here, the instructor discusses how the mixer combines signals from the primary input and the feedback input. It does not change the magnitude but instead affects the phase, acting as a switch that can either add or subtract the feedback signal based on whether it's positive (+1) or negative (‒1).
Examples & Analogies
Imagine adjusting a recipe by either adding or subtracting ingredients. If you taste a dish (output) and decide it needs salt (positive feedback), you add more salt (input). If it’s too salty (negative feedback), you reduce the amount you use next time.
Understanding System Behavior
Chapter 8 of 10
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So, what we said is that, the basic types of feedback system it is, we make say it is ‒ve feedback system or +ve feedback system.
Detailed Explanation
The instructor categorizes feedback systems into two main types: negative feedback (which counters input changes) and positive feedback (which enhances input changes). Understanding these concepts is crucial for students as they describe the system's response to inputs.
Examples & Analogies
Imagine a car's cruise control system. If the speed increases too much (input change), negative feedback slows it down to maintain a steady speed. On the other hand, if the accelerator pedal is pushed (positive feedback), the speed increases, propelling the car faster.
Classifying Feedback Systems
Chapter 9 of 10
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If the created effect coming back to the original point through the feedback path negates the original change then the feedback system it is called ‒ve feedback system.
Detailed Explanation
In a negative feedback system, the feedback signal returns to the input and reduces the effect of the input signal, stabilizing the output. If an increase in input causes a decrease in system response, it classifies as negative feedback.
Examples & Analogies
This can be likened to using a dimmer switch for lights. If you increase the light brightness, but the room feels too bright, you might turn down the dimmer (negative feedback) to stabilize the comfort level of the room.
Positive Feedback Mechanism
Chapter 10 of 10
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Chapter Content
On the other hand in case if the signal it is if the change if the created effect due to a change coming back through the feedback path, if it is aggravating the original change; that means, if it is in the same phase. Then we call the feedback system it is +ve feedback system.
Detailed Explanation
In positive feedback systems, the feedback signal enhances the original input signal. This means if an input change causes an increase in output, the feedback reinforces that output change, creating a loop that can lead to exponential growth in the output signal.
Examples & Analogies
Think of a microphone feedback situation in a concert. If the singer's voice is amplified and gets too close to the mic, it can create a loud screeching noise (positive feedback) that grows louder instead of being dampened.
Key Concepts
-
Basic Model: The feedback system includes a forward amplifier transmitting signals and a feedback path sending part of the output back to the input. The forward gain is denoted as 'A' and the feedback factor as 'β'.
-
Types of Feedback: Two main types are discussed:
-
Negative Feedback: Where the feedback signal counteracts the input signal, stabilizing the system and reducing gain sensitivity.
-
Positive Feedback: Here, the feedback signal enhances the input signal, potentially leading to instability or oscillation.
-
Transfer Characteristics: The derivation of the input-to-output transfer characteristics reveals how feedback affects amplifier gain, particularly highlighting the desensitivity factor, which addresses changes in gain due to feedback incorporation.
-
Significance:
-
Understanding feedback systems is essential for designing reliable and effective analog circuits, as they impact stability, gain, and performance significantly.
Examples & Applications
A typical operational amplifier circuit with negative feedback stabilizes the output and reduces sensitivity to input variations.
In oscillator circuits, positive feedback is employed to generate sustained oscillations, which can lead to waveform generation.
The comparison between a feedback amplifier and a non-feedback amplifier highlights differences in linearity and stability.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Negative feedback, keep it tame, reduces gain, it’s not a game.
Stories
Imagine a teacher correcting a student’s mistake, that's like negative feedback guiding the output to be correct.
Memory Tools
N for Negative feedback = Nurturing Stability; P for Positive feedback = Promoting Change.
Acronyms
FAM for Feedback Amplifier Models
Feedback
Amplifier
Models.
Flash Cards
Glossary
- Feedback System
A system in which a part of the output signal is fed back to the input to influence the behavior of the amplifier.
- Negative Feedback
A type of feedback that reduces gain sensitivity and stabilizes the output by counteracting changes in the input.
- Positive Feedback
A type of feedback that amplifies changes in the input, which may lead to instability or oscillation.
- Desensitivity Factor
A measure that indicates the effect of feedback on reducing the overall gain sensitivity of the amplifier.
- Transfer Characteristic
The relationship between the input and output of a feedback system, defining how the output responds to the input.
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