GATE Electronics|Electrical

What are effects of negative feedback? Ans. It stabilizes gain. Increase BW. Changes the Ri and R0 Decreases voltage gain, Ad Decreases harmonic or non-linear distortion. Decreases effect of input offset voltage at the output Decreases effect of variation in temperature and supply voltage on the output of the output amplifier

Explain the application and limitations of Milliman's theorem. (IES-06) Ans. This theorem provides the equivalent circuits which are either Thevenin's or Norton Equivalent circuits. This theorem is applicable only their independent voltage sources with their internal series impedances connected directly in parallel, or independent current sources with their internal series admittances connected directly in series. Limitations: This theorem is not applicable to circuits where impedances or dependent sources are present between the independent sources. This theorem is not useful for circuits with less than two independent sources.

Mention some examples where the Thevenin's theorem cannot be applied? (IES-06) Ans. This theorem is inapplicable to loads which are magnetically coupled to other parts of the circuit. This theorem is inapplicable for non-linear and unilateral networks. To apply this theorem, the load should not contain any dependent source.

Mention some limitations of the superposition's theorem. Ans. This theorem is not valid for power relationship. This theorem is not applicable to circuits containing only dependent sources. With dependent sources, superposition can be used only when the controlling functions are external to the network-containing sources, so that the controls are unchanged when the sources act at a time.

Mention some examples where the reciprocity theorem is not applicable? Ans: This theorem is inapplicable to unilateral networks comprising of elector tubes or other control devices. This theorem is inapplicable to circuits with time-varying elements. This theorem is inapplicable to circuits with dependent sources. To apply this theorem, we have to consider only the zero-state response by taking all the initial conditions to be zero.

What is the different between direct and indirect band gap semiconductor? Ans. In direct band gap semiconductor, minimum of conduction band and maximum of valence band occurs for same k number while in indirect band gap semiconductor they occur for different k number. GaAs is direct band gap semiconductor while Si and Ge are indirect band gap semiconductors.

What do you mean by word ‘Transistor’? Ans. Transistor means “Transfer + Resistor”. It means transfer of signal from low resistance circuit (i.e. input) to high resistance circuit (i.e. output). What is the main advantage of FET over BJT? Ans.Advantages of FET over BJT are : Thermal runaway does not occur in FET. FET is less noisy than BJT since it is unipolar. FET fabrication takes much lesser area than BJT. What do you mean by term ‘Amplifier’? Is any device can act as amplifier? Ans. Term 'Amplifier' means a device that basically amplify the signal.Since energy can not be generated so no device can work as an amplifier in true sense. The term is itself misleading. All amplifying devices actually work as energy converter. They convert DC energy from supply into AC energy.

A flip-flop is which type of Multivibrator:  Astable, Monostable or Bistable. Ans. A flip-flop is Bistable multivibrator since it has both of its output states stable. Bistable multivibrator, in which the circuit is stable in either state. It can be flipped from one state to the other by an external trigger pulse. This circuit is also known as a flip-flop.  TR1 and TR2  are trigger to change the state.

What is an INHIBIT Gate? Ans. It is basically an AND gate with one of its input negated by an inverter as shown below.