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Interactive Audio Lesson
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Introduction to Feedback and Resistance
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Today, we're diving into the effect of feedback on input and output resistance. Can anyone tell me what feedback in circuits refers to?
Isn't it using the output of a circuit to influence its input?
Exactly! Feedback can help stabilize and control the gain of amplifiers. Now, why do you think input and output resistances are important?
They determine how much of the signal gets into the circuit and what goes out.
Right again! Higher input resistance means less loading of the signal source. Remember the acronym 'HELLO' for Higher input resistance leads to Lesser Output loading. Letβs explore how feedback affects these resistances.
Voltage Amplifiers and Feedback Connections
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Consider a voltage amplifier with a shunt-series feedback configuration. Can anyone identify what the connection looks like?
The voltage input connects in shunt while feedback is in series?
Correct! This setup allows us to derive expressions for input resistance. When feedback is applied, we can say that the input resistance, R_in_f, increases by the expression R_in_f = R_in(1 + Ξ²A). Let's break down the variables involved.
So, increasing R_in means more input signal can flow?
Exactly! More input signal leads to better performance. This is key in designing efficient amplifiers.
Practical Situations with Finite Loads
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Now letβs transition into a practical scenario with a finite load resistance. How do you think this influences our previous equations?
Does it change the way we look at R_in?
Absolutely! The presence of a finite load means we have to factor it in. We can adjust our expression to R_in_f = R_in(1 + Ξ²'A'). Can someone explain what A' represents?
I think A' is the load-affected gain!
Spot on! Understanding A' helps us see how feedback modifies performance in real circuits. Letβs summarize by focusing on these real-world implications.
Summary and Conclusion
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To wrap up our discussion today: Why is feedback significant in circuits?
It helps manage gain and stability in amplifiers.
Correct! And remember the way feedback impacts R_in and R_out? It generally increases input resistance and adjusts output resistance based on circuit configuration. Ensure you grasp these relationships as we progress!
Thanks! That really clears up a lot of the confusion I had.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The interaction of feedback mechanisms in electronic amplifiers plays a critical role in determining both input and output resistances. This section discusses the basics of voltage amplifiers and the impact of negative feedback on these resistances, using ideal and practical examples to explain the underlying principles and formulas.
Detailed
Effect of Feedback on Input Resistance and Output Resistance
In this section, we explore the significant influence of negative feedback on input and output resistances in analog electronic circuits. We begin by considering an ideal voltage amplifier configured with a feedback network. The feedback is classified as shunt-series or voltage-series feedback, where the input port is shunt connected, while the primary and feedback ports are connected in series.
Key Concepts:
- Ideal Feedback Configuration: Assume that the input resistance is infinite and the output resistance is zero at the outset. This simplifies the analysis and helps derive formulas for the input resistance of the feedback system.
- Impact of Negative Feedback: When feedback is applied, the input resistance of the amplifier increases due to the desensitization factor expressed as
$$ R_{in_f} = R_{in}(1 + Ξ²A) $$
where
- R_{in_f} is the feedback system's input resistance,
- R_{in} is the input resistance of the forward amplifier,
- $Ξ²$ is the feedback factor,
- $A$ is the voltage gain of the amplifier.
- Practical Situations: In real-world scenarios, both the load resistance and feedback resistance may have finite values, influencing input resistance and output resistance further. The relationships develop a bit further, replacing $A$ by $A'$ (load affected gain) when these resistances come into play, leading to:
$$ R_{in_f} = R_{in}(1 + Ξ²β²A) $$
By recognizing variations in feedback characteristics in both ideal and practical circuits, students can appreciate how feedback influences amplifier performance, specifically discussing series and parallel configurations and their respective impacts.
Significance of the Section:
Understanding the effects of feedback on input and output resistance is paramount for designing robust electronic circuits. This forms the foundation for further explorations into circuit behavior, performance optimization, and enhancing amplifier stability.
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Audio Book
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Introduction to Feedback Systems
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Yeah. So, dear students, so, welcome back after the break and before the break we were talking about 4 basic configurations of a βve feedback system and we have seen the change of the system gain due to the βve feedback and we have talked about the desensitization factor. Now we are going to talk about the effect of the feedback system on input resistance and output resistance as I have given a hint in the previous part of this lecture.
Detailed Explanation
This introduction sets the context for the discussion on feedback systems. It mentions previous topics on the configurations of negative feedback systems, changes in system gain due to feedback, and introduces the specific focus on how feedback affects both input and output resistance. Negative feedback aims to stabilize and improve the performance of electronic circuits by reducing gain while enhancing linearity and bandwidth.
Examples & Analogies
Think of a thermostat in your home. When the desired temperature is set, the thermostat continuously monitors the temperature and adjusts the heating system accordingly. This feedback loop maintains a stable environment. Similarly, feedback in electronic systems ensures stability and efficiency.
Circuit Configuration for Voltage Amplifier
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So, in the next slide we do have the corresponding circuit diagram here and to start with let we consider a voltage amplifier and its feedback connection it is shunt-series or you can see voltage-series feedback; which means that this port it is shunt and here we do have a series connection here.
Detailed Explanation
In this chunk, we're introduced to a specific configuration of a voltage amplifier with feedback. The configuration discussed is a shunt-series or voltage-series feedback connection. This means that the input to the feedback circuit is taken in parallel (shunt) with the input source, while the output feedback is connected in series with the output.
Examples & Analogies
Imagine a water faucet where you can control the flow of water through a series of pipes. The way you adjust the water impacts the flow rate (input resistance), similarly, feedback configurations adjust the performance of amplifiers.
Initial Ideal Assumptions
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However, to start with for feedback network let we consider it is ideal situation namely; it is input resistance it is infinite and the corresponding output resistance here it is 0.
Detailed Explanation
In an ideal feedback scenario, we assume that the input resistance of the circuit is infinite, meaning that it does not draw any current from the input source, which is ideal for preserving the signal integrity. Similarly, we assume the output resistance is zero, allowing maximum power transfer to the load without loss.
Examples & Analogies
Consider a perfectly insulated container that holds a hot drink. It keeps all the heat in (infinite input resistance), and does not lose any warmth (zero output resistance), maximizing your drink's temperature for longer.
Deriving Input Resistance Change
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Now, let we consider that we are stimulating the circuit with a signal source called v and we are observing the corresponding current entering into the port and let we call this as i_s. And then the input resistance of the feedback system R_in_f is defined by...
Detailed Explanation
This section begins the derivation of the input resistance of the feedback system. A signal voltage 'v' is applied, and it generates a current 'i_s'. The input resistance, denoted as R_in_f, is calculated using these parameters. The relationship R_in_f = R(1 + Ξ²A) shows how feedback affects the input resistance, where Ξ² is the feedback fraction and A is the amplifier gain.
Examples & Analogies
Imagine measuring how much water flows into a tank from a pipe. The resistance of the pipe can change based on the amount of feedback (or water already inside). If more feedback (water) is inside, the flow (input resistance) adjusts according to the systemβs needs.
Voltage Relationships in Feedback System
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So, if you consider say this port and if we are applying say v here and if you consider v_s actually it is equal to summation of v and then corresponding feedback voltage v_in_f...
Detailed Explanation
This chunk discusses the voltage relationships in the feedback system. It shows that the applied voltage (v_s) is a combination of the input voltage (v_in) and the feedback voltage (v_in_f), which is proportional to the internal voltage gain and feedback factor.
Examples & Analogies
Think of a seesaw; the input voltage is one end, while the feedback acts like a counterweight at the other end. The balance of these weights determines how the seesaw tilts, similar to how feedback adjusts the voltage in an amplifier.
Effect of Finite Load Resistance
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Now, let we consider that in practical situation where definitely there may be a finite load R_L...
Detailed Explanation
Here, we transition to practical considerations where the load resistance (R_L) isn't ideal (finite). This finite load affects the voltage at the circuit's output, changing the voltage gain and further modifying the input resistance, leading to a more realistic model.
Examples & Analogies
Imagine trying to fill a bucket with a fixed amount of water (R_L), representing a finite load. Depending on how empty or full the bucket is, the flow rate (voltage) changes, affecting how quickly you can fill it up.
Output Resistance Changes with Feedback
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On the other hand, if I consider the output resistance of the feedback network also...
Detailed Explanation
Within this chunk, the discussion shifts to the output resistance of the feedback network. As the network is introduced into the feedback system, its finite resistance also influences the overall output characteristics, affecting how voltage is delivered to the load.
Examples & Analogies
Think of an electric circuit as a water supply system. Just like how widening a pipe can reduce water pressure (output resistance), the circuitβs design and feedback affect how effectively it supplies power to the load.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Ideal Feedback Configuration: Assume that the input resistance is infinite and the output resistance is zero at the outset. This simplifies the analysis and helps derive formulas for the input resistance of the feedback system.
-
Impact of Negative Feedback: When feedback is applied, the input resistance of the amplifier increases due to the desensitization factor expressed as
-
$$ R_{in_f} = R_{in}(1 + Ξ²A) $$
-
where
-
R_{in_f} is the feedback system's input resistance,
-
R_{in} is the input resistance of the forward amplifier,
-
$Ξ²$ is the feedback factor,
-
$A$ is the voltage gain of the amplifier.
-
Practical Situations: In real-world scenarios, both the load resistance and feedback resistance may have finite values, influencing input resistance and output resistance further. The relationships develop a bit further, replacing $A$ by $A'$ (load affected gain) when these resistances come into play, leading to:
-
$$ R_{in_f} = R_{in}(1 + Ξ²β²A) $$
-
By recognizing variations in feedback characteristics in both ideal and practical circuits, students can appreciate how feedback influences amplifier performance, specifically discussing series and parallel configurations and their respective impacts.
-
Significance of the Section:
-
Understanding the effects of feedback on input and output resistance is paramount for designing robust electronic circuits. This forms the foundation for further explorations into circuit behavior, performance optimization, and enhancing amplifier stability.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
In a voltage amplifier with negative feedback, the input resistance can increase significantly, allowing more of the input signal to be processed without loss.
-
When introducing a finite load to a feedback amplifier, the output resistance might increase, affecting the amplifier's ability to drive loads efficiently.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedbackβs here, it gives a cheer, / Inputβs high, your gain wonβt die!
π Fascinating Stories
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Imagine a see-saw: when one end is pushed up with feedback, the other end lifts higher. This is like increased input resistance thanks to the feedback mechanism.
π§ Other Memory Gems
-
For the key factors remember 'FINDS': Feedback Increases, Negates Decrease Signal-load.
π― Super Acronyms
βR.I.Nβ
- Resistance Increases with Negative feedback!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Feedback
Definition:
A process in which a portion of the output signal is fed back to the input of a system.
-
Term: Input Resistance
Definition:
The resistance encountered by a signal source looking into the input terminals of a circuit.
-
Term: Output Resistance
Definition:
The resistance a circuit presents to the load connected to its output.
-
Term: Desensitization Factor
Definition:
A factor that describes how feedback reduces the sensitivity of the amplifier's gain to changes in input or load conditions.