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Understanding Output Resistance in Voltage Amplifiers
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Today, we're discussing how feedback connections impact the output resistance of voltage amplifiers. Can anyone tell me what happens to output resistance in an ideal situation?
I think it becomes zero because feedback takes over?
Great! In an ideal feedback setup, yes, the output resistance is theoretically zero. Now, if we consider real-world applications, how do finite resistances affect the output resistance?
They would increase the output resistance, right?
Exactly! This concept is crucial for understanding how we can design circuits to maintain desirable output characteristics. Remember, output resistance affects how well the circuit can drive loads, so keep this in mind. Let's move on to derive the output resistance formula.
Values of Gain and Gain Factor Adjustments
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Now that we know how to calculate output resistance, can anyone explain how feedback changes voltage gain?
Does feedback reduce the gain?
Exactly! A feedback factor, denoted as Ξ², modifies the gain, often reducing it to improve linearity and bandwidth. Knowing how to adjust these factors is essential in circuit design.
So, if Ξ² increases, the voltage gain will decrease more?
That's correct! This relationship helps engineers create more stable circuits. Who can summarize the key points we just discussed?
Impact of Non-Ideal Feedback on Circuit Performance
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Let's delve into how non-ideal feedback affects circuit performance. What complications can arise with finite input and output resistances?
It could cause signal loss, making the amplifier less effective?
Exactly, signal loss increases as resistances affect current and voltage levels. This is why we often require ideal conditions in theory but must account for real-world elements.
Are there equations to calculate these factors?
Yes! The output resistance expressions can be derived under various conditions, and it helps us understand the limitations of our designs.
Trans-Impedance and Trans-Conductance Configuration
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Moving on, let's compare trans-impedance and trans-conductance amplifiers. Can someone explain the basic difference between these types?
I think trans-impedance amplifiers convert current to voltage while trans-conductance does the opposite.
Exactly! It's crucial to understand how feedback influences each type's output resistance. Feedback can enhance performance and stability across configurations.
Are the feedback effects similar in both configurations?
Yes, while the signals may differ, the principles of feedback apply similarly. Let's summarize the different configurations and their output effects.
Applications of Feedback in Practical Circuits
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So, why is feedback important in real-world circuits?
It helps stabilize the gain and improve bandwidth?
Exactly! It also reduces distortion and increases linearity. Understanding feedback's role is vital for any electronics engineer!
What kind of feedback do we often apply in practical amplifiers?
Typically, negative feedback is used to achieve stable and predictable performance. Let's conclude our session by reviewing the formulas derived and their applications in circuit design.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, we delve into how feedback connections influence the output resistance of different amplifier configurations, such as voltage amplifiers and current amplifiers. By examining both ideal and non-ideal conditions, we outline the expressions for output resistance, discussing the roles of input and feedback resistances with a focus on voltage-series and current-shunt feedback systems.
Detailed
Feedback System (Part-D)
This section focuses on understanding the impact of feedback connections on output resistance in both voltage and current amplifier configurations. The first part evaluates an ideal voltage amplifier using a shunt series feedback setup. The analysis begins with an ideal feedback network where input resistance is infinite, and output resistance is zero. The output resistance expression is derived by applying Kirchoff's current law, leading to insights into how input and feedback resistances affect the circuit.
We examine various scenarios such as non-ideal cases where source and feedback resistances are finite, discussing their combined effects through adjustments to the gain factors. The principles apply to both trans-impedance and current feedback amplifiers, emphasizing the importance of feedback in modifying amplifier characteristics. By analyzing various configurations, we establish significant formulas that explain output resistance changes and the mechanics of feedback systems.
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Introduction to Output Resistance Changes
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So, yeah dear students, so welcome back after the short break and before the break we are talking about the change of input resistance of the different configuration. And whereas, we are going to talk about change in output resistance to start with let we consider it is a voltage amplifier and we want to see the change due to feedback connection.
Detailed Explanation
In this introduction, we are shifting focus from input resistance to output resistance in feedback systems. The output resistance is vital for understanding how different amplifier configurations react to feedback. We will begin by examining a voltage amplifier's behavior under feedback.
Examples & Analogies
Think of an amplifier as a water faucet. When you turn the faucet (the amplifier) on, it allows water flow (signal) to come out. The output resistance can be compared to how much pressure is lost in the pipes when water is flowing out β we want to see how feedback changes that.
Configuration of Voltage Amplifier with Feedback
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And since it is a voltage amplifier as we have discussed, the circuit is given here. The configuration here it is referred to as shunt series feedback or voltage series Feedback circuit.
Detailed Explanation
This chunk describes the setup of a voltage amplifier. The shunt series feedback configuration indicates how feedback is applied: a shunt connection at the input and a series connection at the output. This configuration affects the input and output resistances of the amplifier.
Examples & Analogies
Imagine a classroom where the teacher (the amplifier) listens and responds to studentsβ questions (feedback). If there are many students (high input resistance), itβs easier for one student to be heard (lower output resistance).
Deriving Output Resistance with Ideal Feedback
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To start with let we consider the feedback network it is ideal namely its input resistance, it is infinite and the output resistance as it is producing voltage, output resistance it is 0.
Detailed Explanation
In an ideal feedback scenario, the input resistance is considered infinite (meaning it does not affect the circuit) and the output resistance is zero (the output can provide unlimited current). These assumptions simplify calculations for output resistance.
Examples & Analogies
Think of an ideal feedback network as a magical wall that doesn't absorb energy, allowing all that gets input through it to flow freely and without resistance, similar to water flowing out of a valve into an open pipe.
Determining Output Resistance from Current and Voltage Relationships
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However, for the forward amplifier we are considering finite input resistance and finite output resistance. We do have the voltage dependent voltage source A_v, v it is appearing at the input of v_in in the forward amplifier.
Detailed Explanation
In reality, amplifiers have finite resistances. We introduce the dependent voltage source, which represents how the output voltage (Av) is influenced by the input voltage (vin). This relationship is essential for calculating actual output resistance.
Examples & Analogies
It's like a special type of water pump that increases its output depending on how much you push the handle (input). The stronger your push (input voltage), the more water (output voltage) comes out.
Stimulation to Measure Output Resistance
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Now, to know the output resistance what we can do? We can stimulate this output port by say voltage source v and then we observe the corresponding current say i and then the port impedance or port resistance it is defined by R_out.
Detailed Explanation
To find output resistance, we connect a voltage source at the output and measure how much current flows in response. The ratio of voltage (v) to current (i) gives the output resistance (R_out).
Examples & Analogies
Imagine you connect a hose to your faucet and measure how much water flows when you apply different pressures. The speed at which water flows gives you an idea of the output resistance of the faucet.
Short-Circuiting the Input Port for Measurement
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So, while we are doing this exercise we have to keep the input port appropriate. So, that it will support the feedback connection, namely we in this case the signal here it is voltage and so, we do have the ideal signal voltage source connected. However, we have to keep its magnitude, signal magnitude should be 0.
Detailed Explanation
For accurate measurement, we must ensure that the input signal is effectively shorted (set to 0). This allows us to isolate the feedback effects without introducing additional variables during output resistance calculations.
Examples & Analogies
Think of testing the resistance of a hose by clamping its end while measuring how much water pressure is applied. This ensures that the pressure reading truly reflects the hose's characteristics, without creating added complications.
Expression of Output Resistance With Feedback Variables
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Now, that is the condition and let we derive the expression of this R_out_f in terms of R_out and probably A and Ξ².
Detailed Explanation
The derivation to express output resistance involves variables such as the original output resistance (R_out) and feedback factors like A (gain) and Ξ² (feedback factor), which determine how feedback influences the output resistance.
Examples & Analogies
It's like tweaking a recipe based on feedback. If everyone says itβs too salty (high A), you might decide to adjust the salt level (Ξ² adjustment) to improve the final dish (output resistance).
Inclusion of Non-Ideal Elements in Output Resistance
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So let me clear yeah. So, if you see if I consider this is short, then if I consider KCL in this mixer what we are getting it is v, input voltage of the amplifier it is β v. But then v it is same as Ξ²v...
Detailed Explanation
When we account for non-ideal elements, like finite source resistance, we realize that each component affects the overall output resistance. This complicates calculations because now we need to consider how much feedback is actually influencing the output.
Examples & Analogies
Imagine adjusting the water flow through multiple taps (resistances) in different rooms. Each adjustment changes how strong the pressure is at the end of each tap (output resistance).
Conclusion and Transition to Non-Ideal Situations
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In that case, we will get the output resistance under this condition, in presence of this R_s, where Ξ²β² it is given...
Detailed Explanation
Here we wrap up the findings for ideal conditions and transition into considering more complex, realistic situations where not all components behave optimally. This signals a shift in focus to analyzing how these non-ideal conditions impact output resistance.
Examples & Analogies
This is like preparing for an emergency by considering possible failures β how does each room (component) react when one tap (part) is not functioning as expected?
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Output Resistance: The impedance presented by the output of an amplifier which influences the load's behavior.
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Feedback Factor (Ξ²): The ratio of the feedback signal to the output signal, critical for gain control.
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Voltage-Series Feedback: A configuration where voltage feedback is applied with a series connection.
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Trans-impedance and Trans-conductance: Different amplifier types that serve specific functions in signal processing.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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An ideal voltage amplifier has an output resistance of 0 Ohms under feedback conditions, allowing it to drive heavy loads effectively.
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In non-ideal conditions, such as with a source resistance of 100 Ohms, the output resistance increases, affecting the gain and performance 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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When feedback flows, resistances drop; volts soar high, signals never stop!
π Fascinating Stories
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Imagine two friends adjusting the volume on a radio; one keeps shouting to the other how loud it is, representing feedback. The radio's output doesnt fall to nothing but stays consistent when they talkβand together, they achieve clarity!
π§ Other Memory Gems
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Feedback factors can be imagined with the acronym VOT: Voltage output feedback adjusts Timing (amplitude) effectively.
π― Super Acronyms
R-F for 'Resistance-Factor' helps remember how feedback impacts the overall resistance in circuits.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Output Resistance
Definition:
The resistance seen by a load connected to the output of an amplifier, influencing the current delivery.
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Term: Feedback Factor (Ξ²)
Definition:
A measure of the fraction of the output signal fed back into the input, used to control gain.
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Term: Voltage Amplifier
Definition:
An amplifier designed to increase the voltage of a signal.
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Term: Transimpedance Amplifier
Definition:
An amplifier that converts input current into a proportional output voltage.
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Term: Transconductance Amplifier
Definition:
An amplifier that converts input voltage into a proportional output current.