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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Common Mode Stimulus
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Today we're going to talk about common mode stimulus in differential amplifiers. Can anyone tell me what they think happens when we apply the same input signal to both terminals?
Does it mean the outputs will be the same?
Exactly! When we feed identical signals, the outputs end up being identical too. This leads us to calculate what we call the common mode gain. That's the measure we use to gauge how these setups behave under uniform input.
So, what is the formula for the common mode gain?
"Great question! The common mode gain, denoted as
Analyzing Common Mode Effects
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Let's analyze the effects of common mode stimulus further. What happens to the signal when we connect the resistors in the circuit?
Wouldn't the output signal stay close to our input signal?
That's correct! As we apply the input in phase, the output closely resembles the input even after connecting resistors. This stability is very interestingβit is a hallmark of common mode input signals.
And how is this different from differential mode?
A vital distinction! In differential mode, we deal with signals that are out of phase. That leads to very different output behavior. Here, we exploit true differences rather than similarities.
Can you share a recap?
Certainly! The application of identical signals produces outputs that remain aligned with the input levels, defining the conditions for stability and elucidating the differences found in dynamic differential mode situations.
Transition to Large Signal Analysis
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As we progress, we consider how large signals contrast against what we've learned about small signals. Why do you think it's important to analyze large signals too?
Is it because large signals can lead to saturation?
Exactly! Large signals can push transistors into saturation. We need to analyze their current states carefully to ensure proper operation and output quality.
What happens to the output when the transistors stop behaving linearly?
The output no longer corresponds directly to input, potentially resulting in clipping. This is why we need to establish a DC operating pointβa balance that allows for maximal signal swing without saturation.
Can we summarize this?
To conclude, we've transitioned to understanding the implications of large signal analysis in our differential amplifier. This helps us anticipate saturation and manage effective operating points.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
This section presents an examination of common mode stimulus in differential amplifiers, detailing how identical signals affect the outputs of the amplifier under various configurations and the concept of common mode gain. Additionally, it emphasizes the significance of analyzing both small and large signal behaviors for accurate performance assessments.
Detailed
Common Mode Stimulus: Detailed Summary
In this section, we explore the phenomenon known as common mode stimulus within the framework of differential amplifiers, focusing on small signal analysis. By applying identical signals (
v_in_c) to both inputs of the amplifier, we investigate the resulting output behavior and how this impacts the performance of the circuit.
The primary observations include:
1. Output Signals: When both inputs receive the same signal, the outputs are found to be equal, leading to the identification of a common mode gain
A_c. The common mode output
v_o_c can be derived as the average of the individual outputs. The main takeaway is that both outputs (
v_o1 and
v_o2) will remain unaffected when identical signals are applied, retaining their respective values.
2. Common Mode Gain: The common mode gain
A_c is characterized by the negative output in relation to input, underlining its negative correlation.
3. Large Signal Analysis: Transitioning from small signal to large signal analysis reveals how meaningful DC voltage levels influence the operation of the transistors, thereby affecting performance. Understanding this relationship is crucial for evaluating whether transistors remain in their active region of operation.
4. Pseudo Differential Stimulus: The section also delves into particular configurations like pseudo differential stimulus, where only one of the inputs is activated to observe the differential outputs. Here, even with significant common mode gain potential, the differential part is expected to dominate when configured properly.
These insights lay the groundwork for deeper understanding in subsequent sections where numerical examples are presented to illustrate practical applications in differential amplifiers.
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Introduction to Common Mode Stimulus
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Yeah. So, welcome back after the short break. So, we are talking about the common mode stimulus. And let us see what happens to the circuit, when we stimulate the circuit with identical signal at the 2 inputs.
Detailed Explanation
In this section, we introduce the concept of common mode stimulus. When we talk about stimuli in electronics, we refer to how we apply voltages or signals to circuit inputs to observe their responses. Here, we specifically examine what happens when identical inputs, or the same signal, are applied to both inputs of a differential amplifier. This is important because a common mode stimulus helps us understand how the amplifier behaves under conditions where both inputs are affected equally.
Examples & Analogies
Imagine two people speaking the same words at the same time in a room. Just as their voices together create a certain effect that can be understood together, applying the same voltage to both inputs results in the amplifier responding based on that combined effect.
Identical Input Signals in the Circuit
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Here we do have the small signal equivalent circuit and here, we like to feed the signal small signal. So, v = v_in_c. Same signal we are feeding here at the other input.
Detailed Explanation
We represent the circuit with a small signal equivalent model. In this model, we define 'v_in_c' as the input voltage applied to both inputs equally. This means that both inputs of the differential amplifier receive the same signal, which helps in analyzing how the circuit functions under these conditions. The circuitβs response can be predicted based on this setup.
Examples & Analogies
Think of a seesaw with two children sitting at either end. If both children weigh the same and push down at the same time, the seesaw remains balanced. Similarly, applying the same signal at both inputs keeps the circuit response balanced.
Effects on the Output Signal
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If we are keeping this is disconnected and if you refer to the circuit here, at the transistor level, this is common source amplifier with degenerator, source degenerator. So, this is the source degenerator and we know its consequence namely the signal coming at its output.
Detailed Explanation
When the circuit inputs receive identical signals, we expect certain effects on the output. Here, the circuit is analyzed closer to its transistor-level implementation, indicating that when a common voltage is applied, the output behaves predictably, affected by the amplification characteristics of the common source amplifier. This means the output will reflect the common mode signals differently compared to differential signals.
Examples & Analogies
It's like a group of friends all saying 'cheese' for a photo at once; their unified expression creates a pleasant outcome in a photograph. Similarly, common mode signals create a coherent effect in an output signal, depending on how the circuit is designed.
Common Mode Gain Definition
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So, I should say that the common mode output if I say, if I take average of v_o2 and this v_o1. So, that gives us the common mode output v_o_c. So, that is remaining same as individual one namely v_in_c Γ A_c.
Detailed Explanation
The common mode output is derived by averaging the outputs from both sides of the amplifier when identical signals are applied. This average determines the common mode output voltage, denoted here as 'v_o_c', which is influenced by the input voltage 'v_in_c' multiplied by the common mode gain 'A_c'. The common mode gain is critical to understanding how the circuit amplifies signals that are the same across both inputs.
Examples & Analogies
Consider someone blending two identical smoothies. The resulting drink will have the same flavor and quality as expected, analogous to how the common mode gain preserves the nature of the input signals when they are the same.
Pseudo Differential Mode Operation
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In case you have say both the signals coming together namely if v_in_c and the differential part namely + and β. If they are coming together, then what happens?
Detailed Explanation
This section discusses a situation where both common mode and differential signals are applied simultaneously to the amplifier. Here, we explore how the outputs are affected by these combined inputs. It emphasizes how even with the common voltage applied, the circuit still responds to differences between the two signals, maintaining the amplifier's functionality.
Examples & Analogies
Think of a sports team playing a game where both teams are trying to win (the differential signals) while the referee keeps ensuring the game rules are followed (the common mode signals). The team strategies play out while still adhering to the common rules.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Common Mode: Signals applied equally to both inputs.
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Common Mode Gain: The output ratio of a common mode stimulus.
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Differential Mode: Signals applied with opposite phases to the inputs.
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 typical differential amplifier setup, if both inputs receive a voltage of 2V, the output will reflect that same input value given the conditions of the circuit.
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When using a common emitter configuration, applying a common signal input leads to an output that closely mimics the input rather than distinguishing the difference.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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For common modes that stay the same, the outputs wonβt have any shame!
π Fascinating Stories
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Imagine two friends throwing the same ball at a wall. They watch as both balls hit and bounce back, they always end matching returns. This reflects how identical inputs yield similar outputs in electronics.
π§ Other Memory Gems
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COMet: Common Output, matching; Mode Equals Two identical inputs.
π― Super Acronyms
CCG - Common Mode Gain, understands that Common is not unique!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Common Mode Gain
Definition:
The gain of a differential amplifier when identical input signals are applied to both inputs.
-
Term: Pseudo Differential Stimulus
Definition:
A technique in which one terminal of a differential amplifier is driven with a signal while the other is grounded, used to analyze differential performance.
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Term: Differential Mode
Definition:
The operation of an amplifier when two different signals are applied to its inputs, leading to the difference in outputs.