Electronic Devices and Circuits : Important interview Questions Part 2

1. 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).

2.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.

3. 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.

4. Why current waveform of capacitor does not start from zero when voltage V_c = 0?

Ans. In the beginning the capacitor acts as short-circuit which indicates maximum current I_c and zero voltage across it, and tghe value of current i s decided by applying KVL at t=0+ condition.

5. 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.

6. In a heavily doped diode which breakdown will occur first?

Ans. Zener breakdown will occur first in the diode since it is related to heavily doped diode. Avalanche breakdown occurs in lightly doped diode.

7. Which transistor configuration is also known as constant current source?

Ans. CB configuration is also known as constant current source since here current gain is approximately 1 so it finds application as a constant current source.

8. What is different between sensor and transducer?

Ans. In transducer the input is some physical quantity like temperature, water level etc and output is either some electrical signal or may be some other physical quantity while in sensor the input may be a physical quantity or electrical signal while output is always electrical quantity.

9. Give two methods to achieve low switching times in a fast recovery diode.

Ans. (a) By Gold diffusion (b) By making the n-region narrow.

10. As the applied forward bias to a p-n junction is increase, the thickness of the depletion region decreases. Does it ever become zero?

Ans. When the forward bias voltage is increased. The width of depletion layer decrease. The depletion layer eventually because thin enough (and not zero) that the electric field cannot counteract charge carrier motion across p-n junction, as a consequence reducing electrical resistance.

11. Emitter follower employs which type of feedback?

Ans. Voltage series feedback, since the output is taken from emitter terminal and emitter resistor acts as feedback resistor.

12. Give three examples of Trivalent and Pentavalent impurities.

Ans. Trivalent impurities are Boron, Aluminium and Gallium while Pentavalent Important are Phosphors, Arsenic and Antimony.

13. What  are the important parameters for high speed OP-Amps?

Ans. High bandwidth, slew rate, differential gain Low settling time and distortion.

14. How many types of resistor are there in diode?

Ans. Two, one is when diode is forward biased while another is when diode is reverse biased.

15. Why input impedance of OP-AMP is very high?

Ans. The first stage of OP-AMP is dual input balanced output whose input impedance is very high that is why input impedance of OP-AMP is very high.

16. In voltage shunt feedback amplifier which parameter is stabilized?

Ans. In voltage shunt feedback amplifier, voltage is sampled and added in shunt to the input so the parameter that is stablized is transresistance.

17. Cross-over modulation is prominent in which type of amplifier and what is the remedy?

Ans. Cross-over modulation is prominent in class B power amplifier. By making current to flow for more than 180˚, This type of distortion can be eliminated, if a class AB amplifier is used through application of constant voltage between base and emitter of each transistor.

18. What is base spreading resistance?

Ans. Large area bipolar transistor can have a very non uniform current distribution due to the resistances of base layer. Since base current is applied through the thin base layer there can be significant series resistance. This resistance is called base-spreading resistance which causes voltage variation across the base.

19. What are the frequency range of Hartley and Collpitt’s oscillators?

Ans. Range of Hartley oscillator- 30 kHz to 30 MHz

       Range of Colpitt oscillator- 20 kHz to 300 MHz

20. Why the negative feedback is used in amplifier?

Ans. Negative feedback is used in amplifier to increase the bandwidth of negative operation so that wider range of frequencies can be amplified.

21. Which type of feedback is found in common collector amplifier?

Ans. Voltage series feedback is used in common collector amplifier.

22. What is the advantage of differential amplifier?

Ans. It helps to reject common mode input i.e. high CMRR. It provides a larger output voltage swing and are less susceptible to common mode noise.

23. What is difference between photo diode and photo voltaic cell?

Ans. Photodiode is illuminated pn-junction diode. It is used to maximum the photo current minimize dark current, and it is sufficiently fast to work as a good photo sensor, while for photovoltaic cell, it is optimized to have the maximum conversion efficiency of incident light to electrical energy.

24. What is small signal analysis (ac analysis)?

Ans. Small signal analysis is performed when signal is of very small amplitude such that operation of non-liner device can be approximated to be linear.

25. What are digital ICs?

Ans. Digital ICs are complete functioning logic network that are equivalents of basis transistor logic circuit. It is complete pre-designed package, it usually requires nothing more than a power supply, input and output.

26. What are examples of DICs(Digital integrated circuits)?

Ans. Gates, counters, multiplexers, demultiplexers, shift registers.

27. What are examples of AICs(Analog Integrated circuits) ?

Ans.   Examples of Analog Integrated circuits are : OP-AMP, amplifiers, filters, frequency multipliers and modulators.

Note : * 741/351 is widely used general purpose OP-AMP.

          *LM380 → special purpose OP-AMPs used only for a audio power applications.

28. What is Monolithic IC?

Ans. Monolithic means ‘One stone’. In monolithic ICs, all component (active and passive) are fabrication on a single piece of semiconductor material, usually silicon. These ICs exhibit good thermal stability because all the component are integrated on the same chip very close to each other.

29. What are Hybrid ICs?

Ans. In hybrid ICs, passive component (such as resistors and capacitors) and the inter connection between them are formed on an insulating substrate. Active components such as transistors diodes, as well as monolithic integrate circuit are then connected to form a complete circuit.

30. What is thin-film and thick hybrid IC?

Ans. When a suitable material is evaporated on a substrate in forming resistors, capacitors and interconnection, a thin-film hybrid IC the resistors capacitors, and interconnection are etched on the substrate by silk screening.

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