47.1. Analog Electronic Circuits

So today, we are going to continue the discussion on Common Collector and Common Drain Amplifiers.

So, the outline of today’s presentation, it is given in the next slide. What we are going to do today it is primarily, we will be focusing on numerical examples and design guidelines of common collector and common drain amplifiers.

In this introduction, the focus is set on continuing the discussion about Common Collector and Common Drain amplifiers, two important configurations in analog electronics. The aim is to present numerical examples and design guidelines related to these amplifiers, building on the knowledge gained from previous discussions.

Think of these amplifiers as different types of engines in vehicles. Just like how different engines are suitable for different types of vehicles, Common Collector and Common Drain amplifiers are suited for specific applications in electronic circuits, and understanding their designs helps optimize their performance.

In fact, I should say that V BB is making a bias at the base terminal and then we do have the DC supply of 10 V. So, V BB is given here, it is 6 V. And then we assume that the thermal equivalent voltage it is 26 mV; then, we are also considering that load capacitance connected at the output node; C L and its value it is say 100 pF.

This part discusses the biasing setup for the amplifier. 'V BB' represents the voltage applied to provide the necessary bias at the base terminal of the transistor. A DC supply of 10 V is connected to the circuit with V BB set to 6 V. The thermal equivalent voltage is a constant value used in calculations, and a load capacitance of 100 pF is included to study how it affects circuit behavior.

Imagine you are trying to start a car engine. The voltage supplied by the battery is like the DC supply for the amplifier. Just as you need a good start to keep the engine running smoothly, biasing the amplifier helps it function correctly in the desired operating range.

So, if I analyze this circuit and if I consider bias current it is, 0.5 mA it is given to us. So, we can say that the collector current, it is also approximately equal to the emitter current. So, that is 0.5 mA,... So, from this one we can see that the transistor, it is in active region of operation.

To find the operating point of the transistor, we consider the bias current, which is given as 0.5 mA. This current flows through the transistor, and because of the nature of bipolar junction transistors, the collector current is nearly equal to the emitter current. By analyzing the voltage drops across the circuit components, we can confirm that the transistor is in its active region, which is necessary for proper amplification.

Consider a train that needs to be on the right track (active region) to function correctly – if it's not in the right place, it won't go anywhere. Similarly, ensuring the transistor is in the active region allows it to amplify signals effectively.

So, let me start going to the operating point first...let us start with g m and you may recall its expression in terms of the quotient current, it is collector current divided by thermal equivalent voltage.

Analyzing small-signal parameters is an important step in amplifier design. The transconductance 'g m' relates the change in output current to the change in input voltage and is calculated using the collector current divided by the thermal voltage. This small-signal model helps design the circuit for desired characteristics like gain and bandwidth.

Think of driving a car where you need precise control of the accelerator (input voltage) to adjust the speed (output current). Just like in driving, understanding and calculating small signal parameters enables you to manage how the amplifier responds to input signals.

Let me clear the space and then again. Let me start with the voltage gain, small signal voltage gain A = v o / v in. So, we may see that this is connected to AC ground.

The voltage gain of the amplifier, denoted as A, is calculated by the ratio of output voltage to input voltage. The setup assumes one terminal is connected to AC ground. Understanding how the gain is derived from small signal parameters helps assess how effectively the amplifier can strengthen signals.

Imagine using a microphone to amplify your voice. The small amount of sound (input) gets transformed into a loud sound (output) that is proportional to your voice. The voltage gain acts similarly, quantifying how much the input signal is magnified.

So, we can say that the upper cutoff frequency now... let me use a different color should see R o / C L.

The upper cutoff frequency is a critical concept in amplifier design, indicating the maximum frequency at which the amplifier can operate effectively without significant loss of gain. This frequency is calculated using the output resistance and load capacitance. Understanding this aspect ensures that the amplifier can handle the frequency of the signals it is meant to process.

Consider a water pipe that can only allow a certain amount of water flow before it gets blocked (loses efficiency). Similarly, knowing the upper cutoff frequency helps in understanding how fast or slow the amplified signals can flow through the amplifier.

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