Circuit Parameters - 98.4.1 | 98. Applications of feedback in amplifier circuits (Part-B) | Analog Electronic Circuits - Vol 4
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Interactive Audio Lesson

Listen to a student-teacher conversation explaining the topic in a relatable way.

Introduction to Feedback in Amplifiers

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0:00
Teacher
Teacher

Today, we are focusing on the role of feedback circuits in common emitter amplifiers. Can anyone explain what feedback is?

Student 1
Student 1

Feedback is when you take part of the output and feed it back to the input.

Teacher
Teacher

Correct! Feedback helps stabilize the circuit. For common emitter amplifiers, we typically use negative feedback. Does anyone know why we prefer negative feedback?

Student 2
Student 2

It reduces the gain but improves stability.

Teacher
Teacher

Exactly! By reducing gain, we can enhance circuit performance. Remember the acronym 'POS' for Positive feedback is 'Over-Feedback', implying instability, while 'NEG' stands for 'Nice and Gainy' which represents the benefits of negative feedback. Let’s move on to configurations such as shunt-shunt.

Feedback Configurations

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Teacher
Teacher

We have different configurations: voltage-shunt and shunt-shunt. Can someone describe these?

Student 3
Student 3

In the voltage-shunt configuration, the output voltage is sampled and mixed with input current.

Teacher
Teacher

Good job! And what about shunt-shunt?

Student 4
Student 4

In shunt-shunt, the currents may drop but they still mix!

Teacher
Teacher

Correct! Using memory aids like 'Voltage Samples, Shunt and Drain – VS-SD' can help remember these configurations. Let’s discuss input and output resistances next.

Calculating Resistances

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Teacher
Teacher

To analyze our amplifier, we need to calculate input and output resistances. What is the significance of knowing these?

Student 1
Student 1

It helps us understand how the circuit will respond to inputs and loads!

Teacher
Teacher

Exactly! When calculating these, factors like load resistances and feedback setup are crucial. Can someone explain how we determine the feedback network's input resistance?

Student 2
Student 2

It involves using the values of the resistances connected to the feedback circuit.

Teacher
Teacher

Yes! Always consider how loading effects can skew these values. Remember, R should be much higher than other resistances to avoid loading effect. Let's summarize our approaches.

Practical Examples and Application

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Teacher
Teacher

Let's go through a practical example. We have given values for our resistances and circuit components. What will be our next steps?

Student 3
Student 3

We will calculate the current and voltages based on the resistances to see how they interact.

Teacher
Teacher

Exactly! This will help us refine our circuit design to ensure optimal performance. Can someone relate how feedback can affect these practical results?

Student 4
Student 4

Feedback will help stabilize our gain and ensure our output is consistent!

Teacher
Teacher

Perfect! Remember the ratios we discussed allow us to bounds values for R for effective amplification.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

This section introduces the concept of circuit parameters in common emitter amplifiers, focusing on feedback configurations and their impact on stabilizing trans-impedance.

Standard

The section discusses the role of feedback in common emitter amplifiers, detailing how negative feedback can stabilize trans-impedance and influence input and output resistances. It emphasizes the importance of proper feedback network design for optimizing amplifier performance.

Detailed

Circuit Parameters: Detailed Summary

In common emitter amplifiers, the circuit parameters, particularly the trans-impedance, are critical for effective amplification. This section highlights the importance of utilizing negative feedback to stabilize trans-impedance in amplifier circuits. The discussion begins with the definition of feedback configurations, particularly focusing on voltage-shunt or shunt-shunt configurations. These configurations facilitate the sampling of output voltage and mixing with input currents, ultimately affecting the amplifier's input and output resistance.

The theoretical foundations of feedback are explored, particularly the conditions required to ensure successful amplification without introducing significant loading effects. The section details how ideal situations where resistances are neglected or treated as ground can lead to simplified calculations. Furthermore, the relationship between circuit resistances is explained, along with applicable formulae for determining the input and output resistance in feedback networks. Practical examples and numerical analyses illustrate these principles, demonstrating how varying circuit parameters impact amplifier performance. To conclude, the necessity of maintaining specific ranges for circuit parameters (like R) is discussed, emphasizing these limits to maintain optimal amplifier functionality.

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Analog Electronic Circuits _ by Prof. Shanthi Pavan
Analog Electronic Circuits _ by Prof. Shanthi Pavan

Audio Book

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Feedback Configuration

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In this circuit, the input signal is current and the output signal is voltage. The forward amplifier's gain is denoted as Z_m, with a unit of Ω, while the feedback network's transfer function Ξ²_FB is measured in β„§. We need to determine the input resistance and output resistance for this circuit configuration.

Detailed Explanation

This chunk discusses the basic parameters of the amplifier circuit, specifically the characteristics of the feedback configuration. The amplifier is taking a current input and producing a voltage output. Here, Z_m represents the gain of the amplifier, while Ξ²_FB expresses how feedback interacts with the amplifier. Essentially, feedback is a technique used to stabilize amplifier performance by controlling the output based on the input. We need to assess the input and output resistances, which are critical for understanding how the amplifier will interact with other components in a circuit.

Examples & Analogies

Think of an amplifier like a water pump. The current input is like the water being pumped into the system, and the output voltage is the pressure generated by the pump. The feedback configuration is similar to adjusting the flow rate to ensure consistent water pressure, allowing for smooth and stable operation.

Resistance Connections

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We need to establish a connection from the output voltage to the input, possibly using a bridging element. This connection will sense the output voltage and convert it into a manageable current for the input port.

Detailed Explanation

This chunk highlights the need to create a connection between the output of the amplifier and its input to facilitate feedback. This connection can often involve bridging elements that help to couple the output voltage with the input current, ensuring signals are transmitted effectively for feedback purposes. By directly linking the output and input, the feedback circuit can stabilize performance and enhance the amplifier's overall response.

Examples & Analogies

Imagine adjusting the thermostat in your home. The thermostat detects the temperature (output) and sends a signal to the heater (input) to adjust the warmth. This feedback loop keeps your home's temperature stable, just like the output and input connections maintain the amplifier's stability.

Resistance Values and Feedback

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Input resistance is represented as r_Ο€, and output resistance is r_o, which experiences loading with resistance R_C, where typically R_C << r_o.

Detailed Explanation

Here, we are assessing the input and output resistance values of the amplifier circuit. The input resistance r_Ο€ determines how much incoming signal can be properly processed by the amplifier, while the output resistance r_o indicates how effectively the output can drive a load. The fact that R_C (the load) is much smaller in comparison to r_o suggests the amplifier will operate with good efficiency and won't be severely affected by the load it drives.

Examples & Analogies

Consider a water hose. The wider the hose (higher resistance), the more water (signal) it can carry without restriction. The load (R_C) is akin to the amount of water you can pour through the hose. If the load is small compared to the hose diameter, water flow remains smooth, just as the amplifier performs well without being overloaded.

Evaluating Feedback Effects

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With the feedback network effectively in place, we can calculate the resulting changes to the input and output resistances and the forward amplifier's gain. This involves examining how the feedback affects the stability and performance of the amplifier circuit.

Detailed Explanation

This chunk focuses on analyzing the impacts of feedback on the circuit parameters. It discusses how feedback helps to stabilize the input and output resistances, which subsequently affects the gain of the amplifier. Evaluating changes helps in ensuring the operational efficiency of the amplifier in different configurations, aiding in achieving desired performance metrics.

Examples & Analogies

Think of an orchestra conductor who adjusts the volume of each instrument to create harmony. The feedback in the circuit serves a similar roleβ€”regulating the performance of various circuit components to ensure they work together smoothly while responding to changes in input.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Feedback Configurations: Various amplifier designs that allow output to be fed back to the input to stabilize or control gain.

  • Input and Output Resistance: Measures of how the circuit behaves when interfaced with others, essential for ensuring compatibility.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • In a shunt-shunt configuration, the output voltage affects the input current, which in turn stabilizes the trans-impedance of the amplifier.

  • A practical example using components such as resistors and capacitors shows how varying feedback alters output parameters in an amplifier.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎡 Rhymes Time

  • Feedback's the key, you see, to gain stability, A shunt or a voltage's the mixed utility.

πŸ“– Fascinating Stories

  • Imagine a band, where the drummer adjusts the volume based on the last song played. This is like our feedback adjusting amplifier performance.

🧠 Other Memory Gems

  • Use 'V-S-Input' to remember voltage shunt configurations. V for Voltage, S for Shunt.

🎯 Super Acronyms

In feedback, remember 'NICE'

  • Negative increases circuit efficiency!

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: TransImpedance (Z)

    Definition:

    The ratio of output voltage to input current in an amplifier circuit.

  • Term: Negative Feedback

    Definition:

    A control mechanism where part of the output is inverted and fed back to the input.

  • Term: Input Resistance (R_in)

    Definition:

    The resistance seen by the signal at the input terminal of the circuit.

  • Term: Output Resistance (R_out)

    Definition:

    The resistance seen by the load at the output terminal of the circuit.

  • Term: Feedback Network

    Definition:

    Components that adjust the feedback provided to the system, which can influence the circuit's characteristics.