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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 + βA). To remember this, think of 'Feedback Increases Resistance' — can anyone repeat that as an acronym?
FIR! Feedback Increases Resistance!
Great! Let's move on to how we apply this in practical systems.
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 + βA’) where A' is the load-affected gain?
Absolutely! This adjustment helps model real-world behavior more accurately. Remember, A’ is key here.
Should we always assume ideal feedback network values or practically consider them?
Always consider real values for better accuracy!
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 + βG). 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 G’ 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.
In a voltage amplifier with feedback, if the input resistance is initially 100kΩ, and βA equals 10, the new input resistance becomes 1MΩ after feedback is applied.
In a current amplifier setup, if the internal gain is 5 and feedback factor β is 0.1, the effective input resistance can be calculated showing feedback's amplifying effects.
Feedback helps resist, input gain cannot miss, increases it is true, consider A and β too.
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.
Use 'FILM' to remember: Feedback Increases Load Management in circuits.
RIB: Resistance Increases with Feedback.
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What is input resistance?
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What does a desensitization factor indicate?
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What is the formula for load-affected input resistance?
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The resistance that is seen by the input source connected to the circuit.
The resistance presented by the output of the amplifier to the load.
The process of routing a portion of the output back to the input to improve the system's performance.
The resistance that is connected to the output of the circuit and can affect the voltage and current.
A factor by which the input or output resistance increases due to feedback mechanisms.
This section discusses the impact of finite load resistance in feedback systems and how it affects input and output resistance of amplifiers.
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.
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 + βA) 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.