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Interactive Audio Lesson
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Understanding Feedback in Common Emitter Amplifiers
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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.
Trans-Impedance and its Role
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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.
Impact on Input and Output Resistances
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Now 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 Ξ²R.
Numerical Example
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Let's examine a numerical example to consolidate our understanding. If R is set to 5kΞ© and Ξ² 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.
Introduction & Overview
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Quick Overview
Standard
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
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 (Z) of the amplifier can be stabilized by the feedback network element, necessitating the relationship A = Z. The feedback configuration discussed is a voltage-shunt or shunt-shunt configuration.
- Input and Output Resistance: The input and output resistances of the common emitter amplifier are driven by the feedback network, impacting overall circuit performance. The input signal is expressed as current while the output signal is voltage, making the analysis of current and voltage relationships crucial.
- AC Grounding: AC grounding is discussed to ensure that operating points are stable under AC signals.
- Effect on Gain Parameters: Introduces how parameters such as input and output resistance are altered by feedback, with emphasis on maintaining practical limits.
- Numerical Analysis: An example is provided with specific values to illustrate how the theory of feedback applies in real circuit situations, reinforcing theoretical concepts with practical understanding.
This section sets the foundation for understanding how negative feedback can improve the stability and performance of amplifier circuits, leading to better design practices in electronic circuit engineering.
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Overview of Feedback Systems
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So far what I said is Z it was Ξ²r , but more important thing is that Zβ² β Ξ²R and Rβ² it is R , R it is r , Ξ² it is . And then next thing as I said that we need to find what is the suitable range of this R.
Detailed Explanation
In this segment, the focus is on understanding the trans-impedance (Z) of an amplifier system. It is mentioned that the original Z can be approximately equal to the transformed version (Z') which involves the resistance (R) in the configuration. The new resistances and current gains are denoted by R' and Ξ², respectively. We also identify the need to determine a suitable operational range for these resistances (R).
Examples & Analogies
Consider the stability of a car's performance based on how much weight it carries. Similarly, in our feedback circuit, ensuring that R remains within a suitable operational range is like balancing the load in a vehicle to ensure stable performance.
Conditions for Effective Feedback
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So, one condition it is that R it should be much higher than R here or Rβ². Likewise to avoid the loading effect here or to ignore the loading effect here the R it is should be much higher than R.
Detailed Explanation
This chunk outlines critical conditions for implementing an effective feedback system in circuits. For stable operation, it specifies that the feedback resistor (R) must be significantly greater than both the output resistance (R') and input resistance. These conditions help minimize loading effects that could distort circuit performance.
Examples & Analogies
Just as a stronger engine helps a truck handle heavier cargo without being strained, a feedback resistor that is much larger helps the amplifier function without negative influences that could distort its output.
Finding the Suitable Range of R
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Now, if I say that these two are defining the lower limit on the other hand if I consider Ξ² Zβ² >> 1 FB which is giving us >> 1.
Detailed Explanation
Here, we discuss how to find the suitable range for the feedback resistance (R). By interpreting the inequalities and conditions discussed earlier, we establish lower and upper limits for R. The lower limit is the minimum resistance necessary for optimal performance, while the upper limit is based on avoiding excessive loading effectsβboth crucial for circuit stability.
Examples & Analogies
Think of setting up a budget for a project. You want a minimum amount to get started (lower limit) and a maximum to avoid overspending (upper limit). Similarly, the resistance values delineate a safe operating 'budget' for our circuit.
Impacts of Feedback on Circuit Parameters
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So, we do have the input resistance we do have the output resistance and also the Z or other let us let you consider directly Zβ² it is Ξ²R = 100 Γ 5 kβ¦ = 500 kβ¦.
Detailed Explanation
This portion details the various impacts of the established feedback configuration on circuit parameters like input and output resistance, along with the feedback system's trans-impedance (Z'). Calculating these values helps illustrate the effects of feedback on circuit performance and efficiency.
Examples & Analogies
It's akin to how the weight of a backpack affects a hiker's performance; similarly, the feedback introduced modifies how the circuit operates under various loads, enhancing or reducing its efficiency.
Practical Example and Conclusion
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So, we can see if I consider D β 10. So, R becomes 0.26 kβ¦ or you may say 260 β¦; in the output resistance on the other hand it is = . So, that gives us a value of 500 β¦.
Detailed Explanation
In conclusion, practical examples are presented to show how theoretical values and calculated effects apply to real feedback circuits. These examples help to concretely illustrate how changes in resistance values influence circuit performance metrics such as input and output resistances.
Examples & Analogies
Imagine a coach adjusting a team's strategy based on the players' performance during a game. The feedback derived from observing the game dictates future adjustments, just as feedback circuits adjust based on performance measurements.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Negative Feedback: A process that helps stabilize amplifiers and improve linearity.
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Trans-Impedance: The relationship of output voltage to input current in an amplifier.
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AC Ground: A reference point in the circuit for stable AC signal performance.
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Shunt Feedback: A feedback configuration that connects across the input terminals.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Example calculation of trans-impedance in a common emitter amplifier using given values of R and Ξ².
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Real-world application where feedback improves amplifier stability in audio equipment.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedback's the key, to stability, in circuits we see, it's a crucial decree.
π Fascinating Stories
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Imagine a race car with a feedback system, adjusting speed and direction, it keeps the car on trackβjust like amplifiers maintain their output.
π§ Other Memory Gems
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S.A.F.E. for feedback: Stabilize, Adjust, Feedback, Enhance. This helps remember feedback's role.
π― Super Acronyms
R.A.I.N. for input/output resistances
- Reduce
- Amplify
- Increase
- Neglectβhow resistances behave in feedback.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: TransImpedance (Z)
Definition:
The ratio of output voltage to input current in an amplifier circuit.
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Term: Negative Feedback
Definition:
A process in which a portion of the output signal is fed back in reverse phase to stabilize the system.
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Term: Common Emitter Amplifier
Definition:
A basic amplifier configuration with high gain, where the emitter is common to both input and output.
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Term: Shunt Configuration
Definition:
A type of feedback configuration where the feedback is connected across the input terminals.
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Term: AC Grounding
Definition:
Establishing a point in the circuit as a reference with respect to AC signals to stabilize performance.