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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Feedback and Trans-Impedance
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Today, we'll explore how feedback stabilizes the trans-impedance in common emitter amplifiers. Can anyone tell me what trans-impedance is?
Is it like how much voltage we get for a certain input current?
Exactly right! Trans-impedance is defined as the relationship between the output voltage and input current. Now, how do you think negative feedback helps in stabilizing this?
Maybe it helps reduce distortion and makes the circuit respond better?
Correct! Negative feedback minimizes variations in output impedance. Let's remember this by using the acronym 'SURE' for Stabilizing, Unifying, Reducing errors!
SURE! Got it!
Good! Letβs dive deeper into the specific configurations now.
Feedback Configurations and Their Effects
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We've established that feedback stabilizes the trans-impedance. Can anyone explain the difference between voltage-shunt and shunt-shunt configurations?
I think voltage-shunt means we're dealing with voltage feedback while shunt-shunt uses current feedback.
Exactly! Voltage-shunt feeds back voltage to control the input while shunt-shunt feeds back a fraction of the output current. Why do you think this matters?
It affects the overall gain and stability of the amplifier!
Right! Let's remember 'VIVA' - Voltage in, Voltage out - for the Voltage-Shunt feedback. Now, letβs explore input and output resistances next!
Calculating Input and Output Resistances
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Now, let's calculate input and output resistance. How can feedback impact these values?
I think it can lower the resistance, especially when something is shunted.
Yes! When the feedback network is applied, the local inputs are reduced, which is crucial for amplifier design. Can anyone provide a formula for these resistances?
I remember R_in = r/(1 + Ξ²Z') and for output, itβs R_out β R_0.
Excellent recap! Remember the phrase 'IN = INt' for Input and Output Nets. Now, as we calculate values, why is it important to have proper loading effects accounted?
To avoid distortion in the output signal!
Exactly! Great job, everyone.
Understanding Feedback Effects on Amplifier Parameters
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Feedback not only stabilizes trans-impedance but also impacts the voltage gain and current gain. Can anyone explain how?
I think it normalizes the gains, so they both appear more consistent.
That's right! It helps maintain a stable A value. Let's call this phenomena 'GAIN' for 'Gains Are In Normality'. What about transconductance? How is it affected?
It's also stabilized, but might increase with negative feedback, right?
Absolutely! This could be thought of as 'accelerating the current control' which is key for effective amplification.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
This section explores how negative feedback in common emitter amplifier circuits leads to stabilization of trans-impedance and the interactions of input and output resistances. It emphasizes the importance of feedback configuration and its components in determining circuit behavior.
Detailed
Applications of Feedback in Amplifier Circuits (Part-B)
In this section, we delve into the specifics of how negative feedback is utilized in common emitter amplifier circuits. The focus is on stabilizing the trans-impedance (Z) and the essential role that feedback networks play in defining and modifying the amplifier output and input characteristics. We categorize the feedback configuration as voltage-shunt or shunt-shunt to define the input and output resistances effectively.
Key Points Covered:
- Trans-Impedance Stabilization: The significance of stabilizing the trans-impedance (Z) through negative feedback, and the relationship between the feedback network elements and amplifier behavior.
- Configuration Types: Explanation of voltage-shunt vs. shunt-shunt configurations, analyzing how these configurations impact the signal input as current and output as voltage.
- Input and Output Resistance Computation: Detailed methods of computing input and output resistance, including incorporating feedback network resistances into the calculations.
- Feedback System Parameters: Discussions around the notable parameters influenced by the feedback system including voltage gain, current gain, and transconductance, and how these are affected by the feedback components.
- Practical Examples: Real-world applications and numerical examples illustrating the effect of varying component parameters in feedback amplification, emphasizing practical limits on resistance values and their impact on circuit response.
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Feedback Network Configuration
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Welcome back after short the break. So, what we are talking about the common emitter amplifier and what we are looking for is that Z trans-impendence of the amplifier we like to stabilize define, it should be defined by the feedback network element. So, as this table suggest that if we are looking for this Z to be stabilized by the βve feedback then A should be Z.
Detailed Explanation
In this chunk, we discuss how the feedback network is crucial for stabilizing the trans-impedance (Z) of the common emitter amplifier. Essentially, for the amplifier to maintain consistent performance, the feedback should be designed in such a way that the gain (A) equals Z, which indicates stability.
Examples & Analogies
Imagine a tightrope walker. Just as the walker uses a pole for balance (feedback), the amplifier uses a feedback network to stabilize its performance, ensuring it doesn't sway (lose stability) under changing conditions.
Voltage-Shunt Feedback Configuration
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So, this is the configuration we have to use, where we need to sample the signal in the voltage form. And we have to mix the signal at the input in the shunt configuration or we can see that the currents fall or we can say it is shunt-shunt configuration.
Detailed Explanation
This chunk introduces the feedback configuration required for the amplifier. It specifies that we will use a voltage-shunt feedback method. In this configuration, the output is sampled and fed back to the input in a way that influences the input current and helps in stabilizing the amplifier's performance.
Examples & Analogies
Think of a team project where one team member brings in resources (voltage signal) that help everyone else take the right steps (mixing at the input). This way, the project stays on track, much like how feedback helps keep the amplifier stable.
Input and Output Resistance
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So, the forward amplifier it is its gain it is Z. So, its it is unit it is β¦ and then the unit of the feedback networks transfer function Ξ² it is a β§.
Detailed Explanation
Here, we clarify the concept of input and output resistance related to the common emitter amplifier. Z represents the amplifier's gain, measured in ohms (β¦), and Ξ², the feedback network's transfer function, is measured in siemens (β§). Understanding these resistances helps in analyzing how much voltage is needed to generate a certain current.
Examples & Analogies
If you think of a water tank (amplifier) where each faucet (input and output) controls the flow of water (current), knowing the resistance helps us calculate how much pressure (voltage) is needed to maintain a consistent flow (current).
Impact of Capacitors and Resistances
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So, here we do have the common emitter amplifier along with its feedback arrangement and we are also adding one capacitor. So, that the DC operating point of the common amplifier it is not getting disturbed by presence of this R.
Detailed Explanation
In this section, we discuss the role of capacitors used in conjunction with feedback resistances. The capacitor helps maintain the stability of the DC operating point of the amplifier, ensuring that the added resistance does not upset the amplifierβs performance.
Examples & Analogies
Consider a musician tuning their instrument. The capacitor acts like a tuner that ensures the sound quality remains true even when other adjustments (resistances) are made, ensuring the performance stays on point.
Thevenin Equivalent Circuit
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So, we can see that this R it is bridging this collector terminal and the base terminal for the signal.
Detailed Explanation
This chunk discusses how to model the amplifier using a Thevenin equivalent circuit. It highlights that the internal components can be simplified to understand their interactions better. The Thevenin equivalent helps in analyzing how various parts of the circuit relate to each other in terms of voltage and resistance.
Examples & Analogies
Think of a complex machine made of various gears and levers. By simplifying it into one equivalent mechanism (Thevenin equivalent), you can understand how the entire machine operates without getting lost in the complexity.
Understanding Feedback Parameters
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So, we can say that Ξ² it is input resistance of the circuit it is r and output resistance in this case it is r.
Detailed Explanation
In this part, we delve into feedback parameters like input and output resistance and how they relate to the entire system's performance. Specifically, it emphasizes that feedback parameters (Ξ²) adjust the effective resistances, impacting the amplifier's behavior.
Examples & Analogies
Imagine two friends working on a project. One friend provides skills (input resistance), while the other offers resources (output resistance). Their collaboration enhances the project's efficiency just as feedback optimizes amplifier performance.
Factors Influencing Range of Resistance
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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.
Detailed Explanation
This section outlines the factors that influence the effective resistance in the feedback network. It stipulates that the designed resistance needs to stay within a specific range to ensure optimal functionality of the amplifier, ensuring that the changes in resistance do not hinder operation.
Examples & Analogies
If you think of a car engine, it needs to operate within certain temperature ranges to function efficiently. Similarly, the feedback network requires its resistances to stay in the optimal range for the amplifier to perform well.
Numerical Example for Resistance Range
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In the next slide, we do have the same example having a specific value of different bias elements as well as the device parameters.
Detailed Explanation
Finally, we provide a numerical example to illustrate how theoretical concepts translate into practical values. By plugging in actual numbers for resistances and feedback components, we see the effects of feedback on the overall function of the amplifier and highlight the importance of finding suitable ranges.
Examples & Analogies
Think of cooking a recipe with precise measurements of ingredients. If you use too much or too little, the dish can fail. Likewise, having the correct resistance range ensures that the amplifier operates properly.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Negative Feedback: Reduces circuit gain and increases stability.
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Trans-Impedance Stabilization: Ensures output voltage is predictable for given input current.
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Voltage-Shunt vs. Shunt-Shunt: Different feedback configurations that impact performance.
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Resistance Changes: Feedback affects both input and output resistances leading to stability.
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Impact on Gains: Negative feedback maintains consistent amplifier gains.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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If a common emitter amplifier has a trans-impedance of 500 kΞ© and feedback is introduced, its trans-impedance may stabilize around 50 kΞ©.
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Applying feedback might a voltage-shunt configuration to yield more predictable voltage outputs while managing current inputs effectively.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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Feedback's like a gentle guide, keeping circuits firm and wide!
π Fascinating Stories
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Imagine a wise teacher (feedback) who helps a student (amplifier) focus on learning (output), avoiding distractions (noise).
π§ Other Memory Gems
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Remember 'GAIN' - Gains Are In Normality for better amplifier performance.
π― Super Acronyms
SURE - Stabilizing, Unifying, and Reducing errors in feedback systems.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: TransImpedance
Definition:
A measure of how a device converts current to voltage, defined as voltage output per unit of input current.
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Term: Negative Feedback
Definition:
A process where a portion of the output is fed back to reduce the gain of the amplifier, enhancing stability.
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Term: Input Resistance
Definition:
The resistance seen by the input signal, influenced by feedback configurations.
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Term: Output Resistance
Definition:
The resistance at the output of the amplifier that the load experiences, also affected by feedback.
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Term: Transconductance
Definition:
The relationship between change in output current to change in input voltage, often impacted by feedback.