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98.5.2. Preparation for Next Lecture
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Today, we'll explore the role of feedback in common emitter amplifiers. Remember, feedback helps stabilize the trans-impedance of the circuit, which is crucial for consistent performance.
How does negative feedback specifically help stabilize the amplifier?
Great question! Negative feedback adjusts the gain of the amplifier, allowing it to respond more predictably. It effectively reduces distortion and improves bandwidth.
What configuration do we use for the feedback network?
We typically use a voltage-shunt or shunt-shunt feedback configuration to sample the output voltage and mix it with the input.
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Trans-impedance is defined as the relationship of output voltage to input current. Does anyone remember the formula relating A and Z?
Is it A = Z?
Exactly! This relationship is crucial as it defines how we aim to stabilize the amplifier's response through our feedback design.
How do we know if we can ignore certain resistances in our calculations?
Good observation! We can ignore resistances if they are significantly higher than others affecting our AC signals, allowing for simpler calculations.
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Create a free accountNow let's talk about how feedback affects input and output resistances. Why is this important?
It affects how much current flows into the amplifier and how much voltage we can expect out.
Spot on! The input resistance typically decreases due to shunt feedback, while output resistance may also change.
What kind of values do we look for in practical designs?
We aim for input and output resistances to be high and low, respectively. Remember, R should be much higher than r, and ideally less than βR.
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Create a free accountLet's examine a numerical example to consolidate our understanding. If R is set to 5kΩ and β is 100, what can we conclude about the output and input resistances?
We should see a decrease in both parameters due to feedback, right?
Exactly! This example emphasizes applying theoretical principles to a real-world scenario, allowing us to see the effectiveness of design choices.
How do we confirm all our calculations are accurate?
Always check against known limits and practical values to ensure everything aligns.
Overview
Short Summary
This section presents the concept of feedback in amplifier circuits, illustrating its significance in stabilizing trans-impedance and input/output resistances.
Medium Summary
In this section, the role of negative feedback in common emitter amplifier circuits is discussed, focusing on how it stabilizes trans-impedance and affects input and output resistances. The necessity of careful configuration in feedback networks is highlighted, alongside practical constraints that guide circuit design.
Detailed Summary
Detailed Summary
In this section of the lecture on Analog Electronic Circuits, the use of feedback in amplifier circuits is critically examined, particularly focusing on forward amplifiers like the common emitter amplifier. Feedback, especially negative feedback, plays a vital role in stabilizing the trans-impedance of such circuits.
Key Points:
- Trans-Impedance Stabilization: The trans-impedance (
Reference YouTube Videos
Key Concepts
Core takeaways and short definitions to help you quickly recall the key ideas from this section.
Negative Feedback: A process that helps stabilize amplifiers and improve linearity.
Trans-Impedance: The relationship of output voltage to input current in an amplifier.
AC Ground: A reference point in the circuit for stable AC signal performance.
Shunt Feedback: A feedback configuration that connects across the input terminals.
Examples
Memory Aids
Interactive tools to help you remember key concepts