OBJECTIVE QUESTIONS IN ANALOG ELECTRONICS

Transcription

1 1. The early effect in a bipolar junction transistor is caused by (a) fast turn-on (c) large collector-base reverse bias (b)fast turn-off (d) large emitter-base forward bias 2. MOSFET can be used as a (a) current controlled capacitor (c) current controlled inductor (b) voltage controlled capacitor (d) voltage controlled inductors 3. Thermal runaway is not possible in FET because as the temperature of FET increases (a) the mobility decreases (c) the drain current increases (b) the transconductance increases (d) none of the above 4. A source follower using an FET usually has a voltage gain which is (a) greater than +100 (b) slightly less than unity but positive (c) exactly unity but negative (d) about A differential amplifier has a differential gain of 20,000. CMRR=80 db. The common mode gain is given by (a) 2 (b) 1 (c) 1/2 (d) 0 6. The approximate input impedance of the OPAMP circuit which has Ri=10k,Rf=100k,RL=10k (a) (b)120k (c)110k (d)10k 7. An OPAMP has a slew rate of 5 V/µ S.The largest sine wave O/P voltage possible at a frequency of 1MHZ is (a) 10 volts (b) 5 volts (c) 5/ volts (d)5/2 volts 8. A change in the value of the emitter resistance Re in a differential amplifier (a) affects the difference mode gain Ad (c)affects both Ad and Ac (b) affects the common mode gain Ac (d) does not effect either Ad and Ac 1

2 9. A differential amplifier is invariably used in the i/p stage of all OP-AMPs.This is dome basically to provide the OP-AMPs with a very high (a)cmrr (b)bandwidth (c) slew rate (d)open-loop gain 10. The effective channel length of a MOSFET in a saturation decreases with increase in (a) gate voltage (b)drain voltage (c)source voltage (d)body voltage 11. Which of the following is not associated with a p-n junction (a) junction capacitance (c)depletion capacitance (b)charge storage capacitance (d)channel length modulation 12. In a p-n junction diode under reverse bias, the magnitude of electric field is maximum at (a) the edge of the depletion region on the p-side (b) the edge of the depletion region on the n-side (c) the p-n junction (d) the center of the depletion region on the n-side 13. An n- channel JFET has IDSS=2mA,and Vp=-4v.Its transconductance gm=(in ma/v)for an applied gate to source voltage VGS=-2v is (a)0.25 (b)0.5 (c)0.75 (d)1 14. In a common emitter, unbypassed resister provides (a)voltage shunt feedback (c)negative voltage feedback (b)current series feedback (d)positive current feedback 15. A constant current signal across a parallel RLC circuits gives an o/p of 1.4v at the signal frequency of 3.89KHZ and 4.1KHZ.At the frequency of 4KHZ,the o/p voltage will be (a)1 v (b) 2v (c)1.4v (d)2.8v 16. Class AB operation is often used in power (large signal) amplifiers in order to (a) get maximum efficiency (c) overcome a crossover distortion (b)remove even harmonics (d)reducing collector dissipation 2

3 17. The bandwidth of an RF tuned amplifier is dependent on (a) Q factor of the tuned o/p circuit (b) Q factor of the tuned i/p circuit (c) (d) Quiescent operating point Q-factor of the o/p and i/p circuits as well as quiescent operating point 18. If =0.98,Ico=6µA and Iβ=100µA for a transistor,then the value of Ic will be (a)2.3ma (b)3.2ma (c)4.6 ma (d)5.2ma 19.The MOSFET switch in its on-state may be considered equivalent to (a)resistor (b)inductor (c)capacitor (d)battery 20. Most of the linear ICs are based on the two-transistor differential amplifier because of its (a) input voltage dependent linear transfer characteristic (b) high voltage gain (c) high input resistance (d) high CMRR 21. Negative feedback in an amplifier a) Reduces gain b) Increase frequency &phase distortion c) Reduces bandwidth d) Increases noise 22. A dc power supply has no-load voltage of 30v,and a full-load voltage of 25v at full-load current of 1A.Its output resistance & load regulation,respectively are a) 5 Ω & 20 % b) 25 Ω & 20 % c) 5 Ω & 16.7 % d) 25 Ω & 16.7 % 23. The current gain of a bipolar transistor drops at high frequencies because of a) Transistor capacitances b) High current effects in the base c) Parasitic inductive elements d) The early effect 3

4 24. The ideal OP-AMP has the following characteristics. a) R i =,A=,R 0 =0 b) R i =0,A=,R 0 =0 c) R i =,A=,R 0 = d) R i =0,A=,R 0 = 25. An npn BJT has g m =38mA/v, c µ =10 14 F, c π =10 13 F and DC current gain β 0 =90.For this transistor f T & f β are a) f T =1.64 x 10 8 Hz & f β = 1.47 x Hz. b) f T =1.47 x Hz & f β = 1.64 x 10 8 Hz c) f T =1.33 x Hz & f β = 1.47 x Hz d) f T =1.47 x Hz & f β = 1.33 x Hz 26. A 741-type OP-AMP has a gain-bandwidth product of 1MHz.A non-inverting amplifier using this opamp & having a voltage gain of 20db will exhibit -3db bandwidth of a) 50 KHz b) 100KHz c) 1000/17 KHz d) 1000/7.07 KHz 27.An amplifier using an opamp with slew rate SR=1v/µsec has a gain of 40db.if this amplifier has to faithfully amplify sinusoidal signals from dc to 20 KHz without introducing any slew-rate induced distortion, then the input signal level must not exceed a) 795mV b) 395mV c) 795 mv d) 39.5mV 28. In the differential voltage gain & the common mode voltage gain of a differential amplifier are 48db &2db respectively, then its common mode rejection ratio is a)23db b)25db c) 46dB d) 50dB 29. Generally, the gain of a transistor amplifier falls at high frequencies due to the a) Internal Capacitance of the device b) Coupling capacitor at the input c) Skin effect d) Coupling capacitor at the output 30. An amplifier without feedback has a voltage gain of 50,input resistance os 1 KΩ & Output resistance of 2.5KΩ.The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedbacik factor of 0.2 is a) 1/11KΩ b) 1/5KΩ c) 5KΩ d) 11KΩ 4

5 31. The action of JFET in its equivalent circuit can best be represented as a a) Current controlled Current source b) Current controlled voltage source c) Voltage controlled voltage source d) voltage controlled current source 32. Three identical amplifiers with each one having a voltage gain of 50,input resistance of 1KΩ & output resistance of 250,are cascaded.the open circuit voltage gain of combined amplifier is a) 49dB b) 51dB c) 98dB d) 102dB 33. An ideal OP-AMP is an ideal a) Current controlled Current source b) Current controlled voltage source c) Voltage controlled voltage source d) voltage controlled current source 34. In a full-wave rectifier using two ideal diodes,v dc & V m are the dc & peak values of the voltage respectively across a resistive load. If PIV is the peak inverse voltage of the diode, then the appropriate relationships for this rectifier is. a) V dc = V m /π, PIV=2V m b) V dc = 2V m /π, PIV=2v m c) V dc = 2V m /π, PIV=V m d) V dc = V m /π, PIV=V m 35. The cascade amplifier is a multistage configuration of a) CC-CB.b) CE-CB c) CB-CC d) CE-CC 36. The current gain of a BJT is a) g m r 0 b) g m / r 0 c) g m r π d) g m /r π 37. The most commonly used amplifier in sample & hold circuits is a) A unity gain non-inverting amplifier b) A unity gain inverting amplifier c) An inverting amplifier with a gain of 10 d) An inverting amplifiers with a gain of 100 5

6 38. Assume that the op-amp of the fig. is ideal. If V i is a triangular wave,then V 0 will be C R V - V 0 a) square wave b) Triangular Wave C) Parabolic Wave d) Sine Wave 39. Introducing a resistor in the emitter of a common amplifier stabilizes the dc operating point against variations in a) Only the temperature b) only the β of the transistor c) Both Temperature & β d) None of the above 40. Voltage Series feedback (also called series-shunt feedback) results in a) Increase in both input & output impedances b) Decreases in both input & output impedances c) Increase in input impedance & decreases in output impedance d) Decrease in input impedance & increase in output impedance Ans:- 1. (c), 2. (b), 3. (a), 4. (a), 5. (a), 6. (d), 7. (d), 8. (b), 9. (a), 10. (b), 11. (d), 12. (c), 13. (b), 14. (c), 15. (b), 16. (c), 17. (a), 18. (d), 19. (c), 20. (d), 21. (a), 22. (b), 23. (a), 24. (a), 25. (b), 26. (b), 27. (c), 28. (c), 29. (a), 30. (a), 31. (d), 32. (c), 33. (b), 34. (b), 35. (b), 36. (c), 37. (b), 38. (c), 39. (c), 40. (c) 6