GATE Electronics|Electrical

What are characteristics of cascode (CE-CB) amplifier? Ans.  characteristics of cascode (CE-CB) amplifier: Same input characteristics as CE Same output characteristics as CB High output resistance High voltage gain Input Miller capacitance effect is at a minimum because Av of CE configuration is very low. No high frequency input occurs from output back to the input. Medium input impedance High current gain More stable Suitable for high frequency applications The amplifier requires large number of resister and capacitor to provide bias

What is current mirror? Ans. The circuit in which output is forced to equal the input current is said to be current mirror. The current mirror is a special case of constant current bias so it can be used to set up constant emitter currents in differential amplifier stages.

Why only h-parameter model is taken for a BJT application as an amplifier? Ans. H-parameter of a transistor are real numbers at audio frequency. Therefore, the reactive part of parameters are absent in h-parameter representation and thus it is computationally simple.

Why input impedance of a JFET is very high? Ans. In JEET, the gate channel junction is always reverse biased so the input impedance is very high. What is the application of a MOSFET in IC technology? Ans. MOSFETs have become one of the principle elements in IC technology today. Their performance has enabled power consumptions in ICs to be reduce. This has reduced. This has reduced amount of heat being dissipated.

What is the difference between controller and compensator? Ans. Both controller and compensator has the function of improving the stability and response of the system. But controller is incorporated in the system during its  manufacturing while compensator is incorporated when system fails to work according to specifications i.e.during its operation.

*What are the time domain methods of determining stability of a system? Ans. Routh stability criterion and root locus are time domain methods for determining the stability of a system.. *What are frequency domain methods to determine the stability of a system? Ans. Polar plot,Nyquist Plot, Bode Plot, Nichlos Chart and Constant M-N circle are frequency domain methods to determine the stability of a system. *Which method is best suitable for showing the change in behavior of a system when a pole is added or removed from system? Ans. Root Locus is best method.

If an unbounded input is applied to system and results in unbounded output then state whether system will be stable or not? Ans. Since input is unbounded so we cannot comment about the stability of system. It may be stable and may be unstable ,for stability bounded input produces bounded output

Explain difference between Photodiode and Solar Cell. A photodiode is made to detect light quickly, a solar cell is made to collect energy from light. They are both typically silicon diodes, but modified to meet their different requirements. A photodiode has to be fast, which means low capacitance, which means small area of silicon. Therefore, it is not very sensitive, and cannot generate much power from light. A solar cell has as large an area as you can afford to buy, getting watts per square inch. There are other differences in the way they are made, and how the PN junction is grown, but they all relate to this difference in purpose.

What is impedance matching and why it is done? Ans.   Impedance matching is the technique the input impedance of an electrical load is made equal to the output impedance of its corresponding signal source to maximize the power transfer from source to load and minimize signal reflection from the load.

What are the uses of Reactive power? Ans.   Reactive power (VARs) is required to maintain the voltage to deliver active power (watts) through transmission lines from the generator. Reactive powers are a must for the flow of active power.  Physical Significance : Reactive power is the power consumed in an ac circuit because of the expansion and collapse of magnetic (inductive) and electrostatic (capacitive) fields. Unlike true power reactive power is not a useful power because it is stored in the circuit itself. This power is stored by inductors, because they expand and collapse, their magnetic fields in an attempt to keep the current constant, and by capacitors because they charge and discharge in an attempt to keep the voltage constant. Circuit inductance and capacitance consume and giveback reactive power. Reactive power is a function of a system's amperage. The power delivered to the inductance is stored in the magnetic field when the field is expanding and returned to the source when the field collapses. The power delivered to the capacitance is stored in the electrostatic field wen the capacitor is charging and returned to the source when the capacitor discharges. None of the power delivered to the circuit by the source is consumed; all is returned to the source. The true power, which is the power consumed, is thus zero. We know that alternating current constantly changes; thus, the cycle of expansion and collapse of the magnetic and electrostatic fields constantly occurs. Therefore, we conclude that reactive power is the rate of energy flow between the source and the reactive components of the load (i.e., inductances and capacitance.) It represents a lossless interchange between the load and the source.