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Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Common Emitter Amplifier
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Today, we're focusing on the common emitter amplifier, particularly its use of a current mirror for biasing. Can anyone explain what we mean by 'current mirror' in this context?
I think a current mirror is a circuit that makes current through one branch follow the current in another branch.
Exactly! We use this in amplifiers to ensure that the current through different transistors remains constant. This stability is crucial for efficient operation. Let's remember: C for 'Current' and M for 'Mirror' β think of it as 'Consistent Matching.'
What happens if the transistors aren't matched?
Great question! Mismatches can lead to discrepancies in current flow, affecting the output voltage. This emphasizes the importance of identical transistors in the mirror. Let's move to how we calculate the output resistance next.
Calculating Output Resistance
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Now, how do we determine the output resistance of our common emitter amplifier?
We can use the small-signal parameters of the transistors, right?
That's correct! For our transistors in active mode, the output resistance can be calculated by combining the resistances of the transistors involved. What values did we find for this configuration?
We found 50kβ¦ for each transistor, leading to a total output resistance of 25kβ¦.
Well done! Remember, R = r1 || r2 gives us this combined resistance, which is essential for calculating voltage gain. Let's discuss how to find that next.
Understanding Voltage Gain
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Who can tell me how we derive the voltage gain for this amplifier?
The voltage gain is calculated by multiplying the transconductance with the output resistance.
Correct! We express voltage gain as A_v = -g_m * R_out. So if g_m is calculated as 1/(26 mV) times the current, what voltage gain did we determine?
It came out to be around 1923!
Excellent recall! This is a notably high gain, emphasizing the effectiveness of our current mirror biasing in amplifiers.
Impact of Early Voltage
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What role does early voltage play in the operation of our common emitter amplifier?
It affects the output voltage, right? If the early voltages for the transistors differ, it can impact the collector current as well.
Exactly! Early voltage helps to stabilize the bias point and affects current reflectivity. A higher early voltage generally provides better performance. Therefore, what's the DC output voltage we've derived here?
We calculated it to be 11.4 V under ideal conditions.
Very good! This aligns with our assumptions, but we must consider real-world factors that can lead to variations.
Mismatches and Evaluations
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What adjustments might we need to make if beta values of our adoptive transistors are not equal?
We would have to recalculate the output current and the resulting output voltage due to potential mismatches.
Exactly! And how would we assess the output performance in such cases?
I suppose we would need to look at the current mirrors more critically, considering their imperfections.
Spot on! Keeping track of even small mismatches is crucial as they can have a big impact. In the end, consistent performance stems from a detailed understanding of these interactions.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, the operation of a common emitter amplifier with a current mirror is analyzed, focusing on how the output resistance and voltage gain are derived. The calculations lead to an understanding of how biasing impacts current flows and the resultant gains.
Detailed
In this section, we explore the use of a common emitter amplifier employing a current mirror as an active load to efficiently bias the amplifier. The current mirror configuration ensures that identical transistors maintain balanced collector currents, which is crucial for maintaining stability in output voltage. The section meticulously calculates the output resistance and voltage gain of the amplifier, considering parameters like transistor betas, early voltage, and biasing resistances. Specifically, the section shows that the output resistance is determined by the small-signal model of the transistors in the active region, yielding values indicative of high performance. Ultimately, it concludes that the expected voltage gain of the amplifier is significantly high, confirming the advantageous use of current mirrors in amplification circuits.
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Introduction to Output Resistance and Voltage Gain
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Now, with this information let us try to find the small signal output resistance and voltage gain of the amplifier. So, we are assuming both the devices are in active region. So, the output resistance R = r β«½ r. Whereas, this r, r = =. So, that is giving us 50 kβ¦. So, same thing we can get for transistor-4, r = 50 kβ¦ and that gives us 25 kβ¦. So, the output resistance it is 25 kβ¦.
Detailed Explanation
In this section, we aim to find the output resistance and voltage gain of the amplifier. To compute the output resistance, we consider both transistors operating in their active region. The relationship for output resistance is that it equals the indicative resistance of the output devices, leading us to the calculated value of 25 k⦠for the circuit under consideration. This output resistance is critical for understanding how the amplifier behaves under load conditions.
Examples & Analogies
Think of the output resistance like the width of a pipe β if the pipe (output resistance) is narrow, it restricts the flow of water (current), making it harder for appliances to work efficiently. A higher output resistance indicates more restriction, which in the context of amplifiers means the circuit can control the output voltage better.
Calculating the Voltage Gain
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Now we like to get what will be the gain of this amplifier. So, the gain of the amplifier of course, the voltage gain of this amplifier it is g R with a β sign. So, what is the value of the g? So, that is, that is the V given there. So, this = β§. So, the voltage gain so, the voltage gain it is, it is close to 2000 rather yeah. So, the gain it is coming 1923.
Detailed Explanation
The voltage gain of an amplifier is quantified by the relationship between the output voltage and the input voltage. Here, we calculate the voltage gain (denoted as 'g') using the formula involving output resistance. With our calculations, we find that the voltage gain of the amplifier is approximately 1923, indicating a significant amplification of the input signal. Such a high gain is typically expected when using an active load, such as a current mirror.
Examples & Analogies
Imagine a microphone amplifying your voice. If your voice is the input signal and the loudspeaker in a concert is the output, high voltage gain means that even a whisper can fill a large hall. This is similar to an amplifier that takes a small electrical signal and makes it significantly larger.
Relationship Between Output Resistance and Gain
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So, as it is expected that since we do have active load. So, the gain it is expected to be very high and the output resistance is also high.
Detailed Explanation
The relationship between output resistance and gain in an amplifier emphasizes that when an active load is used, both output resistance and gain are typically high. This combination ensures the circuit can provide a robust performance under varying load conditions while maintaining fidelity in amplifying the input signal. High output resistance supports the ability of the amplifier to manage voltage levels effectively.
Examples & Analogies
Consider an athlete using specialized shoes designed for optimal performance. Just as these shoes allow for better speed and stability, a high output resistance coupled with high gain ensures that our amplifier can manage signals efficiently and perform well regardless of external changes.
Impact of Early Voltage on Output Voltage
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Now, next part of this question it is to find DC output voltage we need to consider this V, the early voltage very carefully.
Detailed Explanation
In this portion, we stress the importance of Early voltage in determining the DC output voltage in transistor amplifiers. Early voltage impacts the characteristics of the transistor operation; thus, ignoring it may lead to inaccuracies in our calculations of DC output voltage. It plays a crucial role when analyzing the static properties of amplifiers, particularly concerning their ability to maintain stability across varying conditions.
Examples & Analogies
Consider a constant temperature environment for an electronic device β if the environment fluctuates, it can lead to unexpected performance changes. Here, the Early voltage is like that constant temperature; itβs a factor that keeps everything in balance and predictable within an electrical circuit, ensuring stable operations even when other parameters shift.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Common Emitter Amplifier: A configuration utilizing transistors to amplify signals.
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Current Mirror: A technique to maintain constant current through mirroring in amplifiers.
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Output Resistance: This reflects how output voltage responds to load changes.
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Voltage Gain: It indicates how much the amplifier can increase input signal amplitudes.
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Early Voltage: Important for assessing current stability in transistor operation.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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An example of a common emitter amplifier might involve using it for audio signal amplification in a radio transmitter.
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Calculating the output voltage gain of an amplifier configured with a current mirror for biasing could be tested through simulations and real-world measurements.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
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In a circuit with a mirror so bright, current stays true, making gains tight.
π Fascinating Stories
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Once in a circuit, the Current Twins mirrored each other, ensuring the flow was strong; together they forged high gains, unseen but felt in every song.
π§ Other Memory Gems
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Remember C-M for Current Mirror; consistency is key in every circuit's cheer.
π― Super Acronyms
G.C.R. for Gain, Current, Resistance helps you recall amplifier performance essentials.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Common Emitter Amplifier
Definition:
A type of amplifier that uses a single transistor with the output taken from the collector.
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Term: Current Mirror
Definition:
A circuit configuration that replicates current flowing in one branch of a circuit to another, maintaining constant current.
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Term: Transconductance (g_m)
Definition:
The measure of a transistor's ability to convert variations in input voltage to output current.
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Term: Output Resistance (R_out)
Definition:
The resistance offered by the output of an amplifier circuit.
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Term: Early Voltage
Definition:
A parameter that indicates how much the output current of a transistor changes with changes in collector-emitter voltage.
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Term: Voltage Gain
Definition:
The ratio of the output voltage to the input voltage in an amplifier.
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Term: Beta (Ξ²)
Definition:
The current gain factor in a transistor, representing the ratio of collector current to base current.