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Understanding Input Resistance in Feedback Systems
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Today we're delving into how feedback impacts input resistance in our circuits. Can anyone explain what we understand by input resistance?
Isn't it the resistance seen by the source connected to the input?
Exactly! And when we introduce feedback into our system, how do you think it changes?
I think it should increase the input resistance? Is that correct?
Yes! The formula we look at is R_in_f = R_in (1 + Ξ²A). To remember this, think of 'Feedback Increases Resistance' β can anyone repeat that as an acronym?
FIR! Feedback Increases Resistance!
Great! Let's move on to how we apply this in practical systems.
Impact of Load Resistance
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Now, what happens when we have a finite load resistance connected to our feedback system?
Doesn't it change the voltage available at the output?
Exactly right! If load resistance is finite, we need to accommodate that in our calculations. Can anyone derive the new input resistance with this new variable?
So, we consider it as R_in_f = R_in (1 + Ξ²Aβ) where A' is the load-affected gain?
Absolutely! This adjustment helps model real-world behavior more accurately. Remember, Aβ is key here.
Should we always assume ideal feedback network values or practically consider them?
Always consider real values for better accuracy!
Feedback in Current Amplifiers
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Let's shift gears to current amplifiers. How does our previous discussion apply to them?
I guess the principles of feedback still hold? We just have to consider current instead of voltage?
Correct! The input resistance is still affected similarly; we use R_in_f = R_in (1 + Ξ²G). Note that G is the current gain, remember 'GC' for Gain Current.
And does it work the same way if we include finite resistances?
Absolutely! As load resistance increases, feedback becomes more complex, which means our calculations must adjust accordingly.
So Gβ now becomes part of the equation too, right?
Well done! Let's summarize what we learned.
Remember that both input and output resistances behave differently under various configurations. Consider your feedback values and the effects of load resistance.
Introduction & Overview
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Quick Overview
Standard
The section elaborates on the concept of feedback systems in electrical circuits, focusing particularly on how a finite load resistance impacts input and output resistances. It examines both ideal and practical scenarios, showing the derivation of formulas that relate these resistances in the presence of feedback.
Detailed
In feedback systems, understanding how feedback affects input and output resistance is crucial, especially in circuits with finite load resistance. This section explores ideal feedback configurations where input resistance is infinite and output resistance is zero, deriving expressions for adjusted input resistance when load resistance is finite. It discusses various configurations, including voltage and current amplifiers, detailing how alterations in load resistance affect the overall system performance through derived relationships like R_in_f = R_in (1 + Ξ²A) and others. By considering both ideal cases and practical scenarios, insights are provided into designing robust feedback circuits that can handle real-world resistances effectively.
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Impact 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 and due to which the voltage available here at this port it may not be same as internally developed voltage and in that situation what maybe the corresponding change. So, to start with let we consider R it is finite.
Detailed Explanation
In real-world applications, we need to consider that loads attached to circuits often have finite resistance. This resistance impacts the voltage available at the input or output port of an amplifier because it can draw some current, changing the original voltage that was expected from the ideal condition. Therefore, itβs essential to account for this finite load in calculations and expectations regarding circuit performance.
Examples & Analogies
Think of a water tank connected to a garden hose. If you open the hose (representing a load), the water pressure in the tank decreases because the water flows out. The same principle applies here: when a load is connected to an amplifier, it changes the voltage available just like the open hose changes the water pressure.
Voltage Relationships in Finite Load Situations
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So, if we put say R here and then the voltage here v. In fact, this is same as v also. So, v = v = A v Γ right. Or we can rearrange this equation and we may see that this is equal to Aβ² v where Aβ² is the load affected gain of the amplifier.
Detailed Explanation
When we have a finite load resistance, we can analyze the relationship between the input voltage, output voltage, and amplifier gain. The load affected gain (Aβ²) modifies the expected output voltage (v) because the finite resistance will draw some current and therefore, affects how much voltage is developed across the input or output port.
Examples & Analogies
Consider an amplifier to be a water pump. When the pump works without any resistance, it can push water out at a certain pressure (the gain). However, if you connect a narrow hose (representing the load), the pressure decreases (the effective gain is reduced) because more effort is needed to push the water through the constriction.
Effects of Finite Feedback Network Resistance
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So, if I say that i current is flowing and it is entering to the circuit and we do have a resistance of R and across this resistance R we do have v it is getting developed.
Detailed Explanation
When we have finite resistance in the feedback network, this changes the relationship of the current flowing and the voltage developed across it. The feedback current can be affected by the load, which alters the expected output voltage and can complicate how we calculate the input resistance of the system.
Examples & Analogies
Imagine you are trying to pour sand into a funnel (the feedback network). If the funnel is too narrow (high resistance), not all the sand (current) can flow through as expected, leading to a backlog and reducing the overall efficiency of your process (the feedback current).
Desensitization Factor and Input Resistance
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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, or this case.
Detailed Explanation
In feedback systems, particularly with series connections, the overall input resistance can be increased due to the desensitization factor. This factor helps to stabilize the input resistance against load variations. Thus, understanding this phenomenon is crucial when designing circuits to ensure they perform reliably under variable load conditions.
Examples & Analogies
Think of a bicycle with a transmission system. When you shift to a higher gear (representing the series connection), it becomes easier to pedal uphill (increased input resistance). Similarly, in an electronic circuit, when we apply feedback, it can compensate for load variations, making the system more robust.
Practical Load Resistance Impacts
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Now, let me 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 and in that situation what maybe the corresponding change.
Detailed Explanation
In practical applications, load resistance impacts the voltage levels in the circuit. When we have a finite load connected, it can lead to discrepancies between the expected internal voltage gains and the actual voltage observed at the output. This understanding is critical for accurate circuit design.
Examples & Analogies
This scenario can be compared to a phone charger. When you plug a phone into a charger, the current drawn by the phone may not be the same as what the charger is capable of delivering. If you have an old or faulty charger, it might not provide the same voltage and current levels, just as finite load resistance affects voltage levels in circuits.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Finite Load Resistance: Impacts circuit behavior and output voltage.
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Amplifier Configuration: Different configurations yield different results under feedback.
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Desensitization Factor: Indicates the degree of change in resistance due to feedback.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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In a voltage amplifier with feedback, if the input resistance is initially 100kΞ©, and Ξ²A equals 10, the new input resistance becomes 1MΞ© after feedback is applied.
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In a current amplifier setup, if the internal gain is 5 and feedback factor Ξ² is 0.1, the effective input resistance can be calculated showing feedback's amplifying effects.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedback helps resist, input gain cannot miss, increases it is true, consider A and Ξ² too.
π Fascinating Stories
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Imagine a circuit like a busy restaurant where feedback is the waiter ensuring every dish makes it out correctly; the load is the number of diners affecting how fast and efficient service is.
π§ Other Memory Gems
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Use 'FILM' to remember: Feedback Increases Load Management in circuits.
π― Super Acronyms
RIB
- Resistance Increases with Feedback.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Input Resistance
Definition:
The resistance that is seen by the input source connected to the circuit.
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Term: Output Resistance
Definition:
The resistance presented by the output of the amplifier to the load.
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Term: Feedback
Definition:
The process of routing a portion of the output back to the input to improve the system's performance.
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Term: Load Resistance
Definition:
The resistance that is connected to the output of the circuit and can affect the voltage and current.
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Term: Desensitization Factor
Definition:
A factor by which the input or output resistance increases due to feedback mechanisms.