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Interactive Audio Lesson
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Introduction to Feedback Systems
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Today, we'll dive into feedback systems and how they affect circuit performance. Can anyone tell me what the primary advantage of feedback is?
Is it that it stabilizes the gain?
Exactly! Feedback systems help stabilize circuit gains. Now, can you think of any other benefits?
Maybe it also increases input resistance?
Precisely! Negative feedback can increase the input resistance. Remember: higher resistance means less current draw from the signal source, which is beneficial. We often summarize the feedback effect on input resistance with the formula we see in circuits: \( R_{in_f} = R_{in} (1 + Ξ²A) \). Letβs unpack this formula further.
Calculating Input Resistance
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To derive the changed input resistance, remember we start with an input signal. What do we get when we sum the voltages?
Is it \( v_s = v + Ξ²v_{in} \)?
Correct! Then we can express the input voltage based on current. What do we find relating \( v_s \), \( I \), and \( R \)?
Oh, that would be \( v = i R \)!
Spot on! Combining these gives us insight into how feedback changes our input resistance. Understanding this is crucial for circuit design. Any questions before we move to practical loads?
Effects of Practical Loads
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Now, letβs discuss what happens in practical situations when we have finite loads. How might this alter our previous calculations?
I think it makes the voltage at the input port not equal to the internal voltage?
Exactly! If we have a non-zero load resistance, the internal voltage will be affected due to the voltage drop across the load. How does this change our input resistance formula?
We must add terms to account for the load, which might look like \( R_{in_f} = R (1 + Ξ²'A') + R_L \)!
Fantastic! Remember, these adjustments are crucial to ensure accurate circuit performance. Letβs also reflect on feedback configurations β can we see any parallels in different amplifier designs?
Types of Amplifiers
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We have different types of amplifiers using feedback, such as transconductance amplifiers. What should we remember about them?
Their input signal is voltage, but they output current, right?
Exactly! And maintaining low input resistance in these scenarios aids in absorbing maximum current. Can you think of how this feedback alters the gain?
It amplifies structure too, just like the voltage amplifiers but in specific configurations!
Well summarized! Always consider the specific configurations when analyzing feedback effects across amplifiers.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section elaborates on how feedback systems, specifically in voltage and current amplifiers, impact input and output resistance, emphasizing the desensitization factor and the significance of load resistance. It also touches on practical scenarios and ideal approximations for better understanding.
Detailed
Detailed Summary
In this section, we explore the effects of negative feedback in electronic circuits, especially focusing on input and output resistances of various amplifier configurations. We begin by noting that the feedback system can alter both the input and output resistances of an amplifier.
1. Feedback Effects on Input Resistance
- Initially, feedback configurations are theorized under ideal conditions: infinite input resistance and zero output resistance.
- The derivation begins with applying a signal source, resulting in an expression for altered input resistance due to feedback:
$$ R_{in_f} = R_{in} (1 + Ξ²A) $$
where $R_{in}$ is the original input resistance, $Ξ²$ is the feedback factor, and $A$ is the amplifier gain. - Practical circumstances with finite loads necessitate adjustments in our calculations, leading to corrected input resistance formulas under real-world conditions.
2. Sensitivity Factors
- The existence of finite load resistance alters the voltage seen by the amplifier, hence affecting the output resistance and beta values. These real-world considerations lead to:
$$ R_{in_f (practical)} = R (1 + Ξ²'A') + R_{L} $$
where $A' = A_{load}$, adjusted for loading effects.
3. Different Amplifier Types
- The discussion transitions into different amplifier configurations such as current amplifiers and transconductance amplifiers, reaffirming that feedback systems universally enhance input resistance through various configurations, such as shunt or series feedback.
- The effect of feedback on output resistance is also discussed, especially when considering both input port and output resistance adjustability.
Conclusion:
This section extensively illustrates the physics behind feedback mechanisms and forms the foundation for understanding various practical amplifier applications.
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Audio Book
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Introduction to Feedback System
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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
In this introduction, the professor welcomes students back and summarizes the previous discussion on the four configurations of negative feedback systems. The focus now shifts to understanding how these feedback systems affect both the input and output resistances of amplifiers. It's crucial because input and output resistances determine how much voltage and current can be effectively used by the circuit without distortion or loss of signal quality.
Examples & Analogies
Think of this like a conversation in a crowded room. Previous discussions were like a preamble where everyone was adjusting their volume levels (the system gain). Now, we're looking at how the size of the room (input resistance) and how well the room acoustics (output resistance) can allow everyone to hear each other clearly.
Shunt-Series Feedback Configuration
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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
This chunk introduces the shunt-series feedback configuration by discussing a voltage amplifier circuit. In this type of feedback, the shunt connection refers to how feedback is introduced at the input while maintaining a series connection afterward. This specific configuration is important to determine how feedback affects the overall performance of the amplifier, particularly concerning input and output resistances.
Examples & Analogies
Imagine a water pipe (the amplifier) where you add a valve on the side (shunt) to control the flow. You can open or close this valve, and how you set it (feedback) influences how much water flows through the pipe without affecting the diameter of the pipe itself (the series connection).
Ideal Feedback Network 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
Assuming an ideal feedback network means that the input resistance is considered infinite, which implies no loading to the source, while the output resistance is zero, allowing maximum power transfer to the load. This simplification helps in understanding the basic theoretical concepts before delving into real-world imperfections.
Examples & Analogies
You can think of this like an effortless conversation where one person can speak indefinitely without tiring (infinite input resistance), and the other can listen without interruption or distortion (zero output resistance).
Derivation of Changed Input Resistance
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Now, to get this derivation of this input resistance of the feedback system 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.
Detailed Explanation
To derive the changed input resistance with feedback, we apply a signal at the input port and observe the current that flows due to this voltage. This sets the stage for establishing a relationship between the initial input resistance and the modified resistance resulting from the feedback mechanism. By observing how the input voltage and the feedback voltage relate, we can calculate the modified input resistance.
Examples & Analogies
Imagine adding a speaker in a room (the input voltage) and measuring how well people can hear it (the current). If someone turns down the volume of the speaker to avoid distortion (feedback), it changes how loud it sounds to others (input resistance).
Input Resistance with Feedback Voltage
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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_{in} and then corresponding feedback voltage v_{f}.
Detailed Explanation
In this segment, the professor explains how the applied input voltage ({v_s}) is a combination of the original input voltage ({v_{in}}) and the feedback voltage ({v_f}). The feedback voltage is critical because it influences the effective input that the amplifier sees, thus changing the overall performance of the circuit.
Examples & Analogies
Think of your smartphone speaker volume where the output sound (feedback) changes according to the ambient noise and how loud you want your call to be (input voltage). The louder the surroundings, the more you need to increase the volume to maintain clarity.
Effects of Load Resistance
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So, let we consider that in practical situation where definitely there may be a finite load R and due to which the voltage available here at this port it may not be same as internally developed voltage.
Detailed Explanation
Here, the discussion shifts to practical scenarios where load resistances are not ideal and exhibit finite values. This means the output voltage will not match the internal voltage due to the effect of load resistance, which complicates the feedback system's analysis. Understanding this helps prepare students for real-world applications where components may not behave ideally.
Examples & Analogies
Consider trying to charge your phone while using it to play a game; the battery will not charge as effectively due to its usage (the load), which is similar to how added resistance affects a circuit.
Practical Cases: Including Finite Load Resistance
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Now, if we put say R here and then the voltage here v_L. In fact, this is same as v_x also. So, v_L = A v_{in} Γ...
Detailed Explanation
This portion continues by expanding on how the presence of finite resistances changes the dynamics of the input and output voltages in the feedback system. By introducing a load resistance, it is essential to re-evaluate the systemβs performance and modify the previously defined equations to include this factor.
Examples & Analogies
Imagine trying to fill a glass of water while someone is simultaneously drinking from it. The amount of water in the glass (output voltage) will be less than what is coming from the tap (internal voltage) because some is being used elsewhere (finite load resistance).
Output Resistance and Feedback Network
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On the other hand, if I consider the output resistance having some finite value, that gives us the feedback systems input resistance R = R (1 + Ξ²A').
Detailed Explanation
In this section, we look at how a finite output resistance affects the feedback system. The output resistance influences the gain (represented as R) of the feedback system, creating a dependency on both input and feedback variables. The incorporation of feedback is shown to impact the input resistance, adapting to changes in the circuitβs resistance values.
Examples & Analogies
Think of it like a sound system where speakers have certain power limits (output resistance). If you push too much power through them without accounting for their capacity, you risk distortion (changed input resistance).
In Summary: Desensitization Factor's Role
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So, here what we have seen that the series connection the series connection it is making the input resistance getting increased by whatever the desensitization factor; either we consider in this case, or this case...
Detailed Explanation
Summarizing the entire discussion, the professor emphasizes the role of the desensitization factor in increasing the input resistance when feedback is applied. This critical factor showcases how feedback can fundamentally improve system performance, regardless of whether the connections are series or parallel. It highlights the adaptability of systems in response to various configurations of feedback.
Examples & Analogies
Picture adjusting the thermostat in your house (feedback) to modify the heat for better climate control. Each adjustment (input resistance) makes the system respond better to changes in temperature (desensitization).
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Negative Feedback: A mechanism that improves amplifier performance by controlling gain and enhancing stability.
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Input Resistance Changes: Feedback alters input resistance, which can be derived through specific formulas dependent on circuit configuration.
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Desensitization in Amplifiers: The desensitization factor indicates how feedback influences performance metrics, particularly gain.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Example of Voltage Amplifier: When considering an ideal voltage amplifier with negative feedback, the input resistance can be expressed as \( R_{in_f} = R_{in} (1 + Ξ²A) \).
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Practical Load Impact: In a real circuit with a load, the input resistance will need to account for the loadβs effect, altering the simplified formula.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedback brings stability, with gains to amplify, input resistance grows high, lowers the current shy.
π Fascinating Stories
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Imagine a busy restaurant where feedback from diners helps adjust the menu. Just like tweaking the recipe based on guest opinions improves service, negative feedback in circuits helps adjust responses for better performance.
π§ Other Memory Gems
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Remember FINE: Feedback Increases (input) Resistance, Negating Excess current draw.
π― Super Acronyms
RIN = Rate of Input; Negative feedback stabilizes the Input.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Feedback System
Definition:
A system in which a portion of the output is fed back to the input to stabilize and control the gain.
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Term: Input Resistance
Definition:
The resistance seen by a signal at the input port of an amplifier, which affects the loading on the previous stage.
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Term: Desensitization Factor
Definition:
A factor introduced in feedback systems that indicates how much the feedback increases the system's input resistance.
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Term: Current Amplifier
Definition:
An amplifier that produces an output current proportional to its input current.
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Term: Transconductance Amplifier
Definition:
An amplifier where the output current is proportional to the input voltage.