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# Analog Electronics for GATE ECE

Hi Guys,

As per the request from many ECE guys for a post regarding Analog Electronics important topics, I am writing this post for them. Analog Electronics is one of the most important subjects for ECE and also since it is a core subject so it becomes much more important that this subject is covered in detail. But many GATE Aspirants are often confused as to what specifically we need to study from this subject as this subject is very vast in itself. This subject accounts for 10-12 marks in GATE exam and is very important if someone wants to pursue higher studies in Electronics domain. So, to reduce the effort we need to target the topics that are specific to GATE.

Diode Circuits

ECE guys will be very much aware of working of Diode in detail since they would have studied the same in Electronic Devices so they do not need to bother much about it. You can directly start from the current-voltage equation of diode and then proceed to Open Circuit and Short Circuit tests on a diode in order to determine the state of a diode. You can practice around 10-20 problems based on these tests in order to get acquainted with solving multi-diode circuits.

Then you can move onto standard applications of Diodes such as Clippers, Clampers, Rectifiers. You have to cover three categories of rectifiers i.e. Half Wave, Full Wave Center Tapped and Full wave Bridge Rectifiers. In each of these circuits, you must be aware of computing Ripple Frequency, Ripple Factor, PIV, Rectification Efficiency, TUF, etc.  Also, you have to study about rectifiers with the capacitive filter but other filters are not required for GATE.
Then one of the most important concepts in Diodes is the design of Voltage Regulators using Zener Diodes. You can study about various cases such as when Input Voltage is variable when Load is variable etc. Then, at last, you can study the application of clampers i.e Voltage Multipliers.
Prepare for GATE (ECE) Exam from the scratch.
Bipolar Junction Transistors (BJT)

Again because of basic knowledge about Electronic Devices you do not need to study about working of BJT in detail and you can directly come to different configurations of BJT which are Common Emitter, Common Base, and Common Collector and about the various operating modes of BJT which are cut-off, Active and Saturation. Then you can study about biasing techniques in BJT which are Fixed Bias, Self Bias, and Voltage Divider Bias and in each of these configurations you need to understand how to compute the stability factor. By calculating Stability Factor you can determine the relative stability of each configuration. To improve the thermal stability you can also study about Compensation Techniques such as Diode Compensation, Thermistor, and Sensistor Compensation.

Based on this knowledge you can study about DC applications of BJT such as Voltage Regulator by the use of the combination of BJT and Zener Diode. Also the concept of Current Mirror and Current Steering Circuits.

After this, you can start with BJT amplifiers in which you have to study about a small-signal model of BJT and there are three models which are remodel, Hybrid Parameter Model and  Hybrid-pi Model. The first two models are most important and identical because both can be obtained from each other by Source Transformation. You can then determine various parameters of the three configurations of BJT which are Voltage Gain, Input resistance and Output Resistance of the amplifier.

Then you have to study about Frequency Response of the amplifier in which there are two sections which are Low-Frequency Response and High-Frequency Response. In High-Frequency Response you have to study about the concept of Miller Effect and in both the frequency response you need to be clear about determining Cut-off Frequency and Unity Gain Frequency as that can be directly asked in GATE.

Beyond this, you also need to prepare the concept of Multistage Amplifiers such as Cascaded Configuration and Cascode Configuration. In cascade configuration, you need to study about the effect of cascading identical or non-identical stages on cut-off frequency and gain of the amplifier.
MOSFET

If you are clear about the analysis of BJT then understanding MOSFET should be a cakewalk. You have to start from the same point where you started BJT from that is the basics of the device and the current-voltage equation. Then based on characteristics of the device you have to understand the different operating regions of MOSFET which are cut-off, Linear and Saturation. Then you can move onto the biasing techniques of MOSFET which are identical to BJT but the main difference is that Gate current is zero due to insulator between gate and device.

After the biasing you can study about the small-signal model of the device and the best part is that there is only one model that you have to study which is the Hybrid-pi model and you have to understand the amplifier analysis using this model. Also, you must know how to derive certain parameters like Trans-conductance and Output Resistance using DC Analysis. Again you will derive the same parameters as in BJT which are Voltage Gain, Input resistance and Output Resistance for various configurations such as Common Source Amplifier with and without bypass capacitor, Common Drain, and Common Gate Amplifier. Again you have to study about the frequency response of the amplifier and derive the cut-off frequency but once you understand the basic method this won’t be a problem for you if you are able to draw the small-signal model. Then the last part involves multi-stage amplifier i.e. Cascade and Cascode Amplifier.

Feedback Amplifier

In this topic, you have too first study about the basic 4 configurations of amplifiers which are Voltage Amplifier, Current Amplifier, Trans-conductance amplifier, and Trans-resistance Amplifier. Then we have to study different feedback configurations in each of the amplifiers which are Shunt-Series Feedback, Shunt-Shunt Feedback, Series-Shunt Feedback, and Series-Series Feedback. You have to focus on deriving the effect of different feedback on input and output impedance as well as identifying the feedback topology from the circuit realized using BJT or Op-Amp.

Oscillators
This topic begins with the understanding of Barkhausen Criteria and then different types of oscillators such as RC Phase Shift Oscillator, and Wein Bridge Oscillator which are also called as Audio Frequency Amplifier. Then we have to study about the Radio Frequency Oscillator such as Hartley Oscillator, Colpitt Oscillator, Clapp Oscillator, and Clapp Oscillator. You also have to study the stability of Oscillator and Figure of Merit.
Op-Amp
This chapter begins with the study of Differential Amplifiers and then the basic characteristics of Op-Amp such as Offset Voltage and Current, Bias Current, Slew Rate, CMRR, SVRR, etc. Then you have to study about the differences between Ideal and Practical Op-amp. Also, study the model of the practical op-amp which includes Input Resistance and Output Resistance also.
Then comes the most important concept in Op-Amp which is the concept of Virtual Ground. Based on this concept you have to understand the concept of Inverting Amplifier, Non-Inverting Amplifier, Inverting Summer, Non-Inverting Summer, Differentiator, Integrator, Current to Voltage Converter, Voltage Follower, etc. You should be able to solve any random circuit including Op-Amp using this concept.
Then you have to study the non-linear applications of Op-Amp such as Precision Diode, Half Wave Rectifier, Full Wave Rectifier, Log Amplifier, and Anti-log amplifier. Then using this knowledge we can study the concept of Active Filters in which you have to understand the concept of deriving 3-dB frequency and also the nature of filter by comparing the response at 0 and infinite frequency.
Then comes one of the most important concepts that are positive feedback applications of Op-Amp in the form of Schmitt Trigger and then application of Schmitt Trigger to derive Astable Multivibrator, Mono-stable Multivibrator, and Triangle Wave Generator.
555 Timer
In this topic, you have to study the working of 555 Timer IC and the role of various terminals. After getting a basic idea of working you can understand how to realize the Mos-stable and Astable Multivibrator using 555 Timer IC. You have to learn about the time period and duty cycle of these multivibrators.
If you can follow this post and study the topics mentioned in detail then I don’t think there will be any question in Analog Electronics that will trouble you. But make sure to change the mindset and approach this subject from Network Analysis point of view rather than Electronic Devices.