16.1. Analog Electronic Circuits

So, dear students welcome back to this Analog Electronics Circuit. Myself Pradip Mandal from IIT Kharagpur, I am associated with E and ECE Department of the institute. So, we are going through the second module and so, it is continuation of that namely we are going through Analysis of non-linear simple non-linear circuit containing BJT and MOSFET. In the previous sub-module we have seen that the circuit containing BJT how to analyze it and today we will be going to similar kind of analysis, but containing MOSFET, and we will also see what will be the difference.

In this introductory section, the speaker welcomes students back to the course on Analog Electronic Circuits and introduces himself. He mentions that the focus will be on the analysis of circuits containing MOSFETs, contrasting it with the previous discussions on BJTs (Bipolar Junction Transistors). The purpose of this session is to build upon prior knowledge while expanding to new content, specifically how to analyze non-linear circuits with MOSFETs.

Think of learning to drive a car. In the first lesson, you may learn how to drive a manual transmission car (analogous to BJTs), and now, you might be transitioning to learning how to drive an automatic car (analogous to MOSFETs). Both have their mechanics, but the principles of driving remain fundamentally similar.

So, let us see the basic circuit configuration. So, here we do have the example circuit, we called example circuit-1 and you see where we do have supply voltage. Main DC supply voltage V which is giving supply to the drain of the transistor through resistor R DD normally referred as load and at the gate we are applying V G.

This chunk focuses on outlining the basic circuit configuration used for analyzing MOSFET circuits. The main components described include a DC supply voltage connected to the drain of the transistor through a load resistor (R DD) and a voltage (V G) applied at the gate. Understanding this configuration sets the stage for analyzing how the MOSFET operates within the circuit and how it can affect current and voltage.

Imagine this circuit as a water system. The voltage supply is like a water tank (which provides water pressure) connected to a pipe (the load resistor) that allows water to flow through. The gate voltage is like a tap that you can open or close to control how much water flows from the tank through the pipe.

And, we are assuming that the device it is in saturation region which is equivalent to active region of operation of BJT; namely, in the channel if you see the drain end the channel pinch off it is happening.

This section explains the assumption that the MOSFET operates in the saturation region, a critical condition for amplifying signals. In saturation, the channel is pinched off at the drain end, meaning that the MOSFET can operate effectively to control current flow. This is comparable to BJTs operating in their active region, where they can amplify signals.

Consider a water flow scenario where a hose gets pinched. If the flow through the hose meets just the right pressure at the pinch point, water can continue flowing efficiently; this represents saturation. If you pinch too hard, it stops the water (cutting off), just as a MOSFET stops conducting outside its operating region.

And, then the expression of the current I DS of the device can be given by this formula where ( ) it is having important role and in this circuit this V incidentally that is also the same as V GS.

This section delves into how to express the current I_DS flowing through the MOSFET. The equation provided shows that the current is significantly influenced by the voltage at the gate (V_GS), establishing a direct relationship between gate voltage and the resulting drain-source current. This concept is crucial for understanding the behavior of MOSFETs in circuits.

Imagine how the height of a water column affects water pressure. In a similar way, the gate voltage influences the drain-source current (I_DS) in a MOSFET. A higher gate voltage applies more 'pressure' to allow more current to flow.

Now, if you compare the common emitter amplifier circuit which is similar to on this circuit common source amplifier, it is and the circuit just for your reference which it has been discussed previous class; I am also showing the circuit.

This chunk highlights the comparison between MOSFET and BJT circuits. It describes the analogous configurations, such as comparing the common emitter amplifier (BJT) with the common source amplifier (MOSFET). Understanding these comparisons helps students grasp how different transistors impact circuit behavior despite similarities in the type of analysis required.

It's like comparing two similar types of vehicles: a gasoline car and an electric car. Both serve the same purpose (transportation), but they operate differently under the hood. Once you understand how to drive one type (BJT), learning to drive the other (MOSFET) becomes easier.

So, here we have written that this is the; this is the equivalent circuit. So, this is the at this point we do have the V DS and we also assume that this part it is very small.

In this section, the speaker reviews a generalized method for calculating current and voltage in the circuit. It outlines steps to find the drain current (I_DS), analyze voltage drops across resistors, and ultimately arrive at the output voltage (V_DS). This method can help understand many MOSFET configurations and their performance under different conditions.

Think of a recipe where you follow steps to make a dish: first, you gather ingredients (current), then you apply heat (voltage drops over components), and finally, you have a finished dish (output voltage). Falling each step leads to the successful completion of the circuit's expected behavior.

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