Analog Circuits: An Uphill Battle for Electrical Engineers
It is a very important topic for Gate exam. You first have to study the basics of Diode and its current-voltage equation. If you practice problems based on Open Circuit and Short Circuit test problems well then you can easily determine the state of various diodes in a multi-diode circuit. Then you can proceed to applications of diodes such as Clippers, Clampers, Rectifiers. The basic knowledge of rectifiers will help you in Power Electronics as well. You can practice various Diode circuits from Kanodia book and any reference book. Thermal effect on Diode can be left as it is an unimportant topic.
Bipolar Junction Transistor (BJT)
The basics about working of BJT should be studied in brief and not in much detail and you should focus more on finding the Q-point of DC analysis of the BJT. You should focus more on Common Emitter configuration and the biasing methods that you should study are Fixed Bias, Self Bias, and Voltage Divider Bias. After learning biasing, the concept of the amplifier is important. There are many models to solve amplifier problems. But remodel is simple to learn. In GATE exam they ask the question only from this model. Also, you may be asked about different components in the small signal model like Trans-conductance, etc and these parameters can be directly from the DC Analysis. By practicing some question you can master it. BJT amplifier is more important than MOSFET.
For Electrical GATE paper you need not worry about this topic and it can be left out. This has now been removed from ECE GATE syllabus as well and is only asked in ESE now.
In MOSFET, you can learn about the basics of working of the device and then you can move onto the biasing techniques. The same biasing techniques as BJT are used here such as Fixed Bias, Self Bias, and Voltage Divider Bias. The topic about MOSFET amplifier is not needed for GATE electrical and so if you get command on problems based on Biasing then it will be sufficient.
In GATE exam, detailed questions are not asked in this topic. But you should be aware of various topology and its effect on output and input impedance, gain, noise, distortion. Also, you must be able to identify the type of feedback by looking at the circuit which may be a BJT amplifier or an Op-Amp amplifier.
The concept of Operational Amplifier starts with the differential amplifier and its various definition like CMRR, slew rate input biasing current, etc. Out of these CMRR and slew rate is important. Most of the questions are asked from basic op-amp topology. You can solve them by just applying network theory and mostly centered around the concept of Virtual Ground. These are simple and mostly asked in gate exam. You should also be aware of various Filter Designs as well as they can be asked in Control Systems or Network Theory. Also, you should be clear with analysis of Schmitt Trigger as that is one of the most important topics in GATE.
Oscillators and 555 Timer
The various oscillators such as Hartley Oscillator, Colpitt Oscillator and the various Multi-vibrators using 555 Timer are not important from GATE perspective for EE syllabus.