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92.1. Feedback System Input Resistance
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Today, we’re going to explore the concept of input resistance in feedback systems. Can anyone tell me what they think input resistance is?
Is it how much resistance the system has at the input?
Exactly! Input resistance refers to the resistance seen at the input terminals of our feedback system, which can affect the performance of our circuits. Let’s dive deeper into how this is calculated with load-affected transimpedance.
What does load-affected transimpedance mean?
Good question! Load-affected transimpedance, denoted as Z', takes into account how the load impacts the output voltage. Think of it like a reduction factor. Remember the acronym Z' = Z * T, where T represents this attenuation factor.
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To find the input resistance of our feedback system, we need to know how to deal with resistances in parallel. Why do you think resistances are combined this way?
I think it’s because more paths for current can lower the total resistance?
Right again! When resistances are in parallel, they reduce total resistance which influences the voltage across the input terminals. The resulting voltage can ultimately define how efficiently our feedback system operates.
How do we actually calculate it then?
Let’s say we have R1 and R2 in parallel; the formula is 1/R_total = 1/R1 + 1/R2. This can be linked back to our input resistance calculation!
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Create a free accountA common pitfall when discussing input resistance is mistakenly adjusting the feedback factor β. Remember, once we establish β, it shouldn’t change during our calculations. Can anyone remind me why this is crucial?
Is it because we need to keep our feedback consistent?
Exactly! Consistency in β is key for accurate results. If we change it mid-calculation, we may end up with incorrect values for resistance.
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Create a free accountNow that we’ve covered input resistance, how do you think it affects the output resistance?
Maybe they’re linked, since they both relate to circuit performance?
Absolutely! The characteristics of the input resistance can directly impact the output. We’ll explore this relationship in detail after a short break.
Overview
Short Summary
This section discusses the parameters influencing the input resistance of a feedback system, particularly emphasizing the role of load effects and resistances in parallel.
Medium Summary
The section explores the calculation of input resistance in feedback systems, highlighting how load-affected transimpedance and finite resistances together influence this measurement. By analyzing how these resistances combine in parallel, the derivation highlights critical aspects of system performance.
Reference YouTube Videos
Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Input Resistance: Effects circuit performance.
Transimpedance: Converts current to voltage.
Load Effect: Impacts total resistance values.
Parallel Resistance: Reduces total system resistance.
Feedback Factor: Maintains consistency in calculations.