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A short class with Sarah and her students. The other ways are under More.
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Today, we'll explore the common emitter amplifier, a fundamental component in analog circuits. Can anyone explain why common emitter configurations are popular?
They're widely used because they provide good voltage gain.
Exactly! They amplify the input signal effectively. Remember, CEA stands for Common Emitter Amplifier, which you'll find easy to recall. Now, who can describe its basic structure?
It usually consists of a BJT transistor with the input signal applied at the base and the output taken from the collector.
Good job! This setup helps in achieving the desired voltage gain. Let's explore the advantages of using active loads with these amplifiers.
Now, let's discuss current mirrors. Can anyone tell me what a current mirror does?
It replicates a reference current in its output.
Correct! Current mirrors are vital for maintaining reliable biasing in amplifiers. Remember the acronym 'CM' for Current Mirror. Can you explain how they enhance amplifier performance?
By providing an active load, they reduce distortion and increase gain.
Exactly! Fantastic connections to performance improvement. Let's further dissect the small signal model of a current mirror.
In small signal analysis, we need to create a model that simplifies our circuit for AC analysis. Who can describe how we start modeling a current mirror?
We need to identify AC ground and replace power sources with short circuits, right?
Exactly! AC sources get shorted, and DC sources are eliminated. Furthermore, can someone relate this to BJTs and MOSFETs?
For BJTs, we consider r_o and g_m, while for MOSFETs, we use g_m and r_d.
Well put! These parameters are critical for accurate small signal representation. Let's summarize today's discussion before moving on.
Now, let's connect what we learned to active loads in common emitter amplifiers. Can anyone explain the benefit of replacing passive loads with active loads?
Using an active load offers higher output impedance and improved gain.
Precisely! It's all about maximizing performance. Remember, AL represents Active Load. Why is the matching of transistors critical here?
If they aren't matched, the performance can be unpredictable and less efficient.
Great insight! Consistency is key in such configurations. Let's move towards calculating voltage gain in these setups next.
Finally, how do we calculate the voltage gain of our setup?
We apply the small signal model and derive the relationship between output and input.
Exactly! The formula is Av = -g_m * (r_o1 || r_o4). Who can explain the implications of this?
It shows that gain depends on load resistance and transconductance.
Good observation! Understanding this relationship lays the groundwork for effective amplifier design. To summarize, today's discussions covered structure, current mirrors, small signal modeling, and voltage gain calculations.
Amplifier type that provides voltage gain.
Essential for biasing and improving amplifier performance.
Important for analyzing the circuit's behavior under small input variations.
Enhances performance by providing higher output impedance.
Derivable through small signal analysis.
In a common emitter, signals grow tall, with mirrors around them; they won't fall at all.
Imagine two friends, the Current and the Mirror, always watching each other; that's how a current mirror works, always reflecting the exact current to ensure stable performance.
C.E.C. – Common Emitter Circuit: Remember 'C.E.C.' to signify the important parts: Configuration, Current Mirror, and Voltage Gain.
AL – Active Load: Active Loads enhance performance, making them phenomenal for amplifiers.
Term
Current Mirror Function
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Term
Common Emitter Amplifier
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Term
Active Load Benefit
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A circuit that copies a current through one active device by controlling the current in another active device.
An amplifier configuration where the output is taken from the collector and the input is applied to the base.
A circuit that uses active components to improve the performance characteristics of an amplifier.
The ratio of output voltage to input voltage in an amplifier.
A linear approximation of the behavior of a non-linear circuit for small input signals.
The section discusses the implementation of common emitter amplifiers with active loads using current mirrors, emphasizing their operational principles and small signal models.
This section explores the use of current mirrors as active loads in common emitter amplifiers. It delves into the functionality and advantages of these configurations, highlighting small signal models for both BJTs and MOSFETs. Additionally, it addresses how these circuits work in practical scenarios and their significance in improving amplifier performance.
In this section, we delve into the concept of common emitter amplifiers employing active loads facilitated by current mirrors. The discussion begins with an overview of the operational principles of current mirrors and their role in ensuring higher gain in amplifiers while maintaining linearity. The small signal models for both BJT and MOSFET implementations are addressed, providing insights into how these transistors' characteristics affect amplifier performance. We then examine the construction of such amplifiers, focusing on biasing, functionality, and the application of current mirrors to create matched operating conditions. By analyzing the small signal equivalent circuits, students gain a comprehensive understanding of how active loads impact voltage gain and overall output dynamics in amplifiers.