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A short class with Sarah and her students. The other ways are under More.
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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. Let’s explore how feedback affects these resistances.
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 + βA). 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.
Now let’s 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 + β'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. Let’s summarize by focusing on these real-world implications.
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.
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.
When feedback is applied, the input resistance of the amplifier increases due to the desensitization factor expressed as
where
R_{in_f} is the feedback system's input resistance,
R_{in} is the input resistance of the forward amplifier,
is the feedback factor,
is the voltage gain of the amplifier.
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 by (load affected gain) when these resistances come into play, leading to:
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.
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.
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.
Feedback’s here, it gives a cheer, / Input’s high, your gain won’t die!
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.
For the key factors remember 'FINDS': Feedback Increases, Negates Decrease Signal-load.
‘R.I.N’: Resistance Increases with Negative feedback!
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What does the desensitization factor do?
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What is the impact of feedback on output resistance?
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How is input resistance expressed with negative feedback?
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A process in which a portion of the output signal is fed back to the input of a system.
The resistance encountered by a signal source looking into the input terminals of a circuit.
The resistance a circuit presents to the load connected to its output.
A factor that describes how feedback reduces the sensitivity of the amplifier's gain to changes in input or load conditions.
This section explains how negative feedback affects the input and output resistances of analog electronic circuits.
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.
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.
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
where
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 by (load affected gain) when these resistances come into play, leading to:
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.
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.