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Feedback Connections in Voltage Amplifiers
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Today, we'll discuss how feedback connections in voltage amplifiers affect output resistance. Can anyone tell me what happens when we connect feedback to an amplifier?
I think it stabilizes the gain?
Exactly! It helps in stabilizing the gain. Now, in an ideal situation, the feedback network has infinite input resistance and zero output resistance. What do you think happens in non-ideal situations?
The resistances could lower the gain, right?
Correct! It modifies the output resistance, leading us to derive new expressions for our systems under various conditions. Let's remember the acronym 'FIRE' for Feedback Input Resistance Effects!
What does 'FIRE' stand for?
'FIRE' reminds us that feedback can change Input Resistance Effects! Remember, in practical circuits, we often deal with finite resistances.
Understanding Source Resistance (R_s)
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Letβs now focus on source resistance (R_s). Who can explain why we consider source resistance when calculating output resistance?
I guess it's because it affects how much voltage the load receives?
Precisely! The voltage division with source and feedback network resistances modifies the voltage at the input. How do we mathematically express this?
Using KCL and the voltage divider rule!
Well done! The voltage can be expressed as v_in = -Ξ²v_x. Now, when we introduce R_s into the expression, we also need to redefine our beta. Can anyone summarize how we do this?
We get a new beta, Ξ²' where it's affected by R_s.
Non-Ideal Feedback Circuit Analysis
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Now that we have established the base concepts, letβs look at a non-ideal circuit with an R_s. How does this influence our feedback configuration?
It changes our output resistance, right?
Correct! Output resistance (R_out) now becomes a function of R_s and the original expressions we derived. What about an example where both output and input resistance are finite?
That would involve adding them in a way that highlights how they influence each other!
Exactly! Remember, when dealing with series and parallel configurations, we must carefully analyze how they impact overall circuit performance.
Trans-Impedance Amplifier
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Letβs transition to trans-impedance amplifiers, where the signal flow and feedback differ significantly. What's special about this configuration?
The input is a current and the output is a voltage?
Yes! And this changes how feedback is applied. What can you tell me about the effect of feedback on output resistance in these circuits?
It still modifies the output resistance, but now we're calculating in terms of voltage gain as opposed to current!
Exactly! We often rewrite the output resistance formula as R_out = R_m (1 + Ξ²G). Remember 'M-G' for 'Mixing Gain Impact' when analyzing these effects!
Real-World Applications of Feedback
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Before we wrap up, letβs discuss real-world applications of these circuits. How does feedback apply in practical scenarios?
In audio amplifiers, feedback helps reduce noise and improve sound quality!
Great example! In applications like these, understanding the non-ideal factors becomes crucial. Can anyone think of a situation where neglecting source resistance could cause issues?
If we ignore it, the actual gain could be much lower than expected!
Exactly! Always remember to account for all resistances in your circuit designs for accurate performance.
Introduction & Overview
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Quick Overview
Standard
The content highlights how feedback connections in voltage amplifiers can alter output resistance, focusing on non-ideal situations involving source resistance and additional network resistances. Various configurations are analyzed to deduce practical output resistance expressions.
Detailed
Non-ideal Situations and Source Resistance
In electronic circuits, especially those involving feedback systems, it is critical to understand how non-ideal conditions affect performance. This section delves into various configurations of voltage amplifiers, primarily focusing on the impact of feedback connections on output resistance.
- Basic Configuration: Initially, an ideal feedback configuration is discussed, where input resistance is infinite, and output resistance is zero. As we introduce practical non-ideal factors, we see changes in these resistances. In voltage amplifiers, the feedback networkβs source resistance plays a pivotal role in defining the feedback circuit's output resistance.
- Non-Ideal Situations: The section explores how the introduction of a source resistance (R_s) alters the voltage at the input port (applying KCL principles). The proportion of voltage distributed across various impedances in the feedback network leads to a revised relationship involving new beta values (Ξ²') and resultant expressions for output resistance.
- Other Configurations: More configurations like that of trans-impedance amplifiers and current amplifiers are also addressed. Each case considers non-ideal components' impact on output resistance, ultimately leading to expressions that account for these resistances and their configurations. The effectiveness of these configurations in maintaining manageable output resistance while maintaining the desired gain is critical for engineers.
This topic is essential for understanding real-world applications of feedback in electronic circuits, particularly in designing amplifiers that need to maintain specific performances under varying loads.
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Introduction to Non-ideal Situations
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So, let us consider non ideal situations to start with let we consider that we do have a source resistance called R_s.
Detailed Explanation
In this chunk, we introduce the concept of non-ideal conditions that can affect the performance of electronic circuits. Specifically, we mention that there exists a source resistance (R_s), which could affect the output resistance of the circuit in various configurations. This is important because ideal scenarios assume no resistance, but real components will have some resistance that can alter circuit behavior.
Examples & Analogies
Think of it like a water pipeβif the pipe is perfectly smooth, water flows freely (ideal situation). But if there are bumps or leaks (source resistance), the water flow will be reduced (non-ideal situation).
Effect of Source Resistance on Input Voltage
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In this condition; v_in, the input voltage at this port can be written in terms of Ξ²v_x. In fact, it is β Ξ²v, and then the voltage appearing here is a part of this voltage.
Detailed Explanation
This chunk explains how the input voltage (v_in) changes when a source resistance is present. The input voltage becomes a function of the feedback factor (Ξ²) and another voltage (v_x). This dependence shows that the presence of source resistance alters how we calculate input voltage in the circuit, which will ultimately influence the output.
Examples & Analogies
Imagine a car engine that needs fuel (voltage). If there's a filter (source resistance), less fuel reaches the engine, affecting its performance. The same goes for the voltageβless ideal conditions lead to lower input voltage.
Current Flow and Relationship with Resistance
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So, we can say that i = β Ξ²β²v, where Ξ²β² = Ξ² Γ R_y / (R_s + R_y).
Detailed Explanation
In this chunk, we relate the current (i) flowing through the circuit to the input voltage and the feedback factor after considering the source resistance. The relationship shows that the feedback factor Ξ² can also change due to the presence of resistances in the circuit, implying that output current is now dependent on both the input conditions and the resistances involved.
Examples & Analogies
Picture a crowded event where a limited number of entry points (electrical resistances) affects how quickly people (current) can enter. More entry points allow for smoother flow, while fewer make it harder. The current flow changes based on these resistances.
Finishing Touches with Series Resistance
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So, we need to put plus R_out_Ξ² and the corresponding Ξ² we can call it is Ξ²β²β².
Detailed Explanation
This chunk wraps up the discussion by indicating the adjustments made to account for output resistance in the feedback circuit. It notes that as resistance factors are introduced one by one, the cumulative effects are considered, allowing us to derive a new feedback parameter (Ξ²β²β²) that reflects these changes.
Examples & Analogies
Think of adjusting the pressure of water flowing through various pipes that lead into a sink. The more pipes you have (series resistance), the more you need to account for pressure loss based on how many exits there are (Ξ²). Each change in resistance alters the flow.
Final Thoughts on Non-ideal and Real Situations
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So, if I consider all the three non-ideal factors, then I will be getting the R_out = R_in_Ξ² + R_out_Ξ².
Detailed Explanation
This final chunk summarizes the overall impact of combining multiple non-ideal factors. It emphasizes that output resistance will depend on a sum of contributions from different parts of the circuit, showing how real-world scenarios complicate the ideal conditions that might have initially been assumed.
Examples & Analogies
Just like cookingβa recipe may work perfectly in isolation, but multiple ingredients (like spices, heat levels, and timing) influence the final dish. Similarly, in electronic circuits, various resistances impact performance, leading to a final output that may differ from the expectations set by ideal conditions.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Feedback: A method used in circuits to enhance stability and control gain.
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Output Resistance: Influenced significantly by feedback and source resistance, critical for circuit performance.
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Non-Ideal Conditions: Real circuits face resistance from components, which alters ideal calculations.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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In a voltage amplifier with a source resistance of 50 ohms, the output voltage diminishes due to voltage division between the source and feedback network.
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In a trans-impedance amplifier, when the input current is increased, the output voltage adapts based on the feedback constant multiplied with the gain of the amplifier.
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 thread, weaves circuits tight; Stabilizing gain, making things right.
π Fascinating Stories
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Imagine a city with traffic lights. The lights change (feedback) to control the flow of cars (gain) effectively. If the lights malfunction (non-ideal conditions), traffic chaos ensues!
π§ Other Memory Gems
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Use the acronym 'FIRE' to remember: Feedback Input Resistance Effects, signifying how feedback influences input resistance performance.
π― Super Acronyms
M-G = Mixing Gain Impact, reminds you that changing input/output parameters alters feedback effects.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Feedback
Definition:
A process where a portion of the output signal is fed back to the input to control the gain and stability of a system.
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Term: Voltage Amplifier
Definition:
An electronic amplifier that increases the voltage of an input signal while preserving its original form.
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Term: Output Resistance
Definition:
The resistance of a device or circuit measured from its output terminal.
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Term: Source Resistance (R_s)
Definition:
The intrinsic resistance seen at the input of an amplifier circuit, which can affect voltage division.
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Term: TransImpedance Amplifier
Definition:
An amplifier that converts an input current to an output voltage.