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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Feedback Configuration Types
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Today, we're focusing on feedback configurations in common emitter amplifiers. Can anyone tell me what a feedback configuration is?
Is it the way we connect feedback to the amplifier to control its gain?
Exactly! There are primarily two types: voltage feedback and current feedback. In our case, we're looking at the voltage-shunt configuration. Can anyone explain why we use this one?
Because it stabilizes the output voltage and ensures consistent gain?
Right! This setup samples the output voltage to control the input current effectively.
So, does that mean we can control the trans-impedance with this configuration?
Good question! Yes, precisely! The trans-impedance Z becomes defined by the feedback network, ensuring stability. In feedback circuits, we often remember: Z = A * R_f, where A is the gain.
To summarize, feedback configurations like voltage-shunt help stabilize our amplifiers by controlling how feedback from the output informs the input.
Calculating Input and Output Resistance
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Now let's discuss how to calculate input and output resistance in our circuit. Can someone tell me about the role of feedback resistors here?
Are they used to determine how much current flows through the circuit?
Absolutely! They help define the input resistance, which can be seen as R_in = r + R_f, where R_f is the feedback resistor. What's crucial is knowing when to ignore those biases.
So, when do we ignore them?
You generally ignore bias resistance in small signal analysis when it is negligible compared to R_f. This results in simplified calculations.
Can anyone tell me the implications on the output resistance?
It gets reduced when using feedback, right?
Correct! The output resistance is also impacted, guiding how we design the feedback network effectively.
Quick recap! Remember, R is used in calculating Z and helps us stabilize trans-impedance, influenced by our feedback network.
Choosing Feedback Resistor Values
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Today, let's explore how we choose our feedback resistor values. Why do you think itβs important?
To ensure the circuit performs optimally without distortion?
Exactly! We aim for R_f to be over ten times greater than any load resistance to avert loading effects. How can we represent this mathematically?
R_f should be greater than 10 * R?
Right! And we also need to ensure that the product of beta and Z' exceeds one for stability.
What happens if we don't meet those limits?
If those limits aren't met, we could face instability, fluctuating gain, or increased distortion. Quickly, let's review: always check that our feedback resistors fit within suitable ranges to maintain effective performance.
Practical Application of Feedback Resistors
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Finally, letβs apply what we've learned to a numerical example. Can anyone recall our ideal resistor configurations?
We learned R_f has to be much higher than R to avoid loading issues.
Precisely! When we set R to 50kΞ©, we satisfy both upper and lower limits of resistance. What result do we get regarding the output resistance?
It becomes lower than the original values, right?
Exactly! So, in summary, choosing the right feedback resistor helps stabilize and optimize gain while managing output effectively. Be sure to apply these principles in real-world circuits!
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section discusses the significance of selecting suitable feedback resistors in common emitter amplifiers, emphasizing the relationship between feedback configurations, input and output resistances, and the overall trans-impedance of the amplifier. Key criteria for selection and formulas for calculating effects on gain and resistance are presented.
Detailed
Detailed Summary
In this section, we delve into the essential role of feedback resistors in amplifier circuits, particularly in common emitter configurations. We aim to stabilize trans-impedance, denoted as Z, using negative feedback. The narrative begins with understanding how feedback networks can stabilize amplifier performance by appropriately defining the feedback configuration (voltage-shunt or shunt-shunt).
Key Concepts Covered:
- Trans-Impedance Stabilization: The feedback configuration influences the forward amplifier's gain (A) and the trans-impedance (Z) is stabilized by the feedback network.
- Feedback Configuration: The shunt configuration allows for the mixing of output and input signals. The voltage sampled from the output is mixed at the input to ensure stability.
- Input and Output Resistance Calculation: The detailed equations for input and output resistance of the circuit are derived, highlighting the importance of bias and feedback resistors.
- Suitable Range for Feedback Resistors: Criteria for selecting the resistance values that avoid loading effects, ensuring robustness, and maintaining circuit performance are discussed.
- Practical Examples: The section provides numerical examples illustrating how to determine the suitable range of feedback resistors, considering real-world parameters such as load and gain requirements.
- Feedback Effect on Parameters: The effect of feedback on voltage and current gains, and the calculation of individual resistances after feedback are also tackled, emphasizing that certain parameters remain unchanged while others are significantly influenced.
Through systematic approaches and detailed calculations, the section aims to equip students with a clear understanding of the interactions between feedback resistors, gain, and stability within analog electronic circuits.
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Definition of Suitable Range
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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
This chunk introduces the concept of finding the suitable range for the feedback resistor R in the circuit. It establishes that the feedback systemβs trans-impedance Z is related to the resistances Ξ², r, and R. When considering practical applications, it's necessary to define what values of R will maintain the desired circuit performance.
Examples & Analogies
Imagine tuning a musical instrumentβif the string is too loose (resistance too low), the sound is flat; if it's too tight (resistance too high), the sound is sharp. In a circuit, similar principles apply where finding the right balance of resistors leads to optimal functioning.
Conditions for Feedback Resistor R
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And to get that since we are sensing the signal here the voltage. So, one condition it is that R it should be much higher than R here or Rβ². Likewise in_Ξ² out out 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 section lays out the conditions for selecting the feedback resistor R. It is crucial for R to be significantly greater than both the input and output resistances (in_Ξ² and out_Ξ²). This ensures that the loading effect, which can degrade circuit performance, is minimized, allowing for more accurate signal amplification.
Examples & Analogies
Think of a highway toll booth, where if too many cars (too low resistance) stop to pay tolls, traffic jams occur. Similarly, if the feedback resistor isn't sufficiently high, it causes delays (loading effects) in signal processing and can alter the expected outcomes.
Desensitization Factors
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And whenever do we say it is much higher than this, all practical purposes what we can do we can see that R β₯ 10r or 10R.
Detailed Explanation
This chunk introduces the practical guideline that the feedback resistor R should be at least ten times greater than the internal resistance r or R. This rule of thumb helps ensure that the circuit operates effectively without significant distortion or errors due to feedback conditions.
Examples & Analogies
Consider a restaurant where the waiter takes orders. If each table (R) can serve ten guests (r) at once, then ensuring each table can handle at least ten guests means smoother service. This concept ensures the circuit can handle input variations without becoming overloaded.
Upper Limit Condition for R
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On the other hand if I consider the other condition namely Aβ²Ξ² should be much higher than 1. And we can say that Ξ²R and Ξ² on the other hand it is it is we want this should be much higher than 1 or we can say that R it is much lower than Ξ²R.
Detailed Explanation
This part describes the upper limit condition for R. It emphasizes that for effective feedback control, the product of the forward gain Aβ² and the feedback factor Ξ² must exceed 1, indicating that the feedback shouldnβt overpower the systemβs gain. Thus, R should also be lower than Ξ²R, ensuring effective performance.
Examples & Analogies
Imagine managing a team. If your lead (Ξ²) has high influences (feedback), the team (R) shouldn't try to overpower the leaderβotherwise, decisions become unclear and chaos ensues. Balancing authority ensures smooth operation.
Combined Limits for Practical Application
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So, if I combined say this lower limit and upper limit of R to really make this feedback system effective we can get a suitable range of R.
Detailed Explanation
Here, the importance of combining the lower and upper limits for R is highlighted. This avoids operational failures by ensuring R stays within a functional range defined by previous conditions. Specifically, this balance is crucial for reliable circuit performance.
Examples & Analogies
Just like setting the temperature on a thermostat requires both a minimum and maximum to maintain comfort, selecting the feedback resistor also needs limits to ensure the circuit remains within a working range.
Conclusion of Suitable Range
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And once you get that and once you make sure that both these conditions are satisfying then we can say Z = . And that can be well approximated by considering by ignoring this 1 with respect to this. So, we can say this is approximately = . So, it is giving us R.
Detailed Explanation
This concluding part identifies that, when both previously established conditions are satisfied, it can be concluded that the trans-impedance Z stabilizes to be approximately equal to R, which is vital for successful circuit operation.
Examples & Analogies
Imagine a balancing scale. When both sides (conditions) add equal weight, the scale remains stable. Similarly, when the resistor conditions are met, Z stabilizes, leading to efficient circuit functioning just like the scale after balancing.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Trans-Impedance Stabilization: The feedback configuration influences the forward amplifier's gain (A) and the trans-impedance (Z) is stabilized by the feedback network.
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Feedback Configuration: The shunt configuration allows for the mixing of output and input signals. The voltage sampled from the output is mixed at the input to ensure stability.
-
Input and Output Resistance Calculation: The detailed equations for input and output resistance of the circuit are derived, highlighting the importance of bias and feedback resistors.
-
Suitable Range for Feedback Resistors: Criteria for selecting the resistance values that avoid loading effects, ensuring robustness, and maintaining circuit performance are discussed.
-
Practical Examples: The section provides numerical examples illustrating how to determine the suitable range of feedback resistors, considering real-world parameters such as load and gain requirements.
-
Feedback Effect on Parameters: The effect of feedback on voltage and current gains, and the calculation of individual resistances after feedback are also tackled, emphasizing that certain parameters remain unchanged while others are significantly influenced.
-
Through systematic approaches and detailed calculations, the section aims to equip students with a clear understanding of the interactions between feedback resistors, gain, and stability within analog electronic circuits.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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Example of selecting R_f = 50 kΞ© which meets performance criteria, resulting in a stable feedback system.
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Calculation demonstrating how altering R_f affects overall circuit output resistance.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedback helps stabilize, oh so fine, / Without loading, our circuits shine.
π Fascinating Stories
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Imagine a carpenter measuring lengths. If his measuring tape is off, every cut will be wrong. Resistors are like that tapeβthey ensure accurate cuts in voltage and current.
π§ Other Memory Gems
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Remember: F.A.C.E (Feedback, Amplifier, Circuit, Efficiency) represents the essentials of amplifier stability.
π― Super Acronyms
R.S.V.P (Resistance Should Validate Performance) to remind us that resistor values need to help performance.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: TransImpedance (Z)
Definition:
A parameter representing the relationship between output voltage and input current in an amplifier.
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Term: Feedback Resistor (R_f)
Definition:
Resistor used in feedback circuits to regulate the signal and improve amplifier performance.
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Term: Input Resistance (R_in)
Definition:
The combined resistance that the input sources observe at the input terminal of the amplifier.
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Term: Output Resistance (R_out)
Definition:
The resistance seen by the load connected to the output of the amplifier.
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Term: Current Gain (A)
Definition:
The ratio of output current to input current in an amplifier.