VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur

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VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur 603 203.

ANBARASAN, AP(OG)/ECE EC 6202 ELECTRONIC DEVICES AND CIRCUITS UNIT-I: PN JUNCTION DEVICES PN junction diode structure, operation and V-I characteristics, diffusion and transient capacitance -

1 VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING QUESTION BANK SUBJECT : EC 6202 Electronic Devices and Circuits SEM / YEAR: III / II nd year EEE Prepared by: N. RAJESH, AP (OG)/ECE, A. ANBARASAN, AP(OG)/ECE EC 6202 ELECTRONIC DEVICES AND CIRCUITS UNIT-I: PN JUNCTION DEVICES PN junction diode structure, operation and V-I characteristics, diffusion and transient capacitance - Rectifiers Half Wave and Full Wave Rectifier, Display devices- LED, Laser diodes- Zener diode characteristics-zener Reverse characteristics Zener as regulator PART A Q.NO QUESTIONS BT LEVEL DOMAIN 1. Model diffusion capacitance in PN junction diode and explain? BTL 3 2. What is a rectifier? Name its types? 3. How to represent the symbol of the following PN diode, Zener diode, LED, UJT 4. Find the diffusion capacitance for a silicon diode with a 15 ma forward current, if the charge carrier transit time is 70ns. 5. With suitable expression what is transition capacitance and Diffusion capacitance? BTL 3 6. Construct the laser diode and give its applications. BTL 3 7. Define storage time. 8. List out the factors on which barrier potential depends? BTL 4 9. Discuss the effect of temperature on reverse saturation current of a diode? BTL6 10. Outline transformer utilization factor and state its value for HWR and FWR? 11. Compare and contrast between p-n junction diode and zener diode? BTL Explain the terms knee voltage and breakdown voltage?

2 13. Explain peak inverse voltage 14. Interpret the term diffusion capacitance or storage capacitance 15. Illustrate the LED symbol. 16. A silicon diode has a saturation current of 7.5 μa at room temperature to 300 K. Estimate the saturation current at 400 K BTL Distinguish between Zener Breakdown and Avalanche breakdown BTL What is meant by dynamic resistance of diode? 19. A Ge diode has a saturation current of 10μA at 300ᵒ K. Determine the saturation current at 400ᵒK. 20. Show the VI characteristics of Zener diode PART B 1. i) Describe the action of a full wave rectifier using diodes and give waveforms of input and output voltages (7) ii) Show the expression for a ripple factor in a full wave rectifier with resistive load. (6) 2. Briefly enumerate the following i) Laser diodes ii) Zener diode as a voltage regulator (7+6) BTL6 3. With neat sketch explain the construction, operation and its characteristics of PN junction diode. Also list its advantages, disadvantages and its applications. (13) BTL3 4. i) Outline the working of bridge rectifier. Give the expressions for RMS current, PIV, Ripple factor and efficiency (7) ii) Illustrate the construction of LCD (6) 5. i) With necessary diagrams, explain the forward and reverse characteristics of PN junction diode (6) ii) Show the circuit diagram of a half wave rectifier for producing a positive output voltage. Explain the circuit operation and sketch the waveforms. (7) i) Make use of a diagram, explain the energy band diagram of an open circuited PN junction and obtain the expression for E 0. (8) ii) Distinguish between Avalanche and Zener break downs (5) BTL2 BTL2 The diode current is 0.6 ma when the applied voltage is 400 mv and 20 ma when applied voltage is 500 mv. Determine efficiency. Assume kt/q= 25mA (13) BTL5 (i) Explain the construction and working principle of Light Emitting Diodes. (8) (ii) The reverse saturation of a silicon PN junction diode is 10μA. Calculate the diode current for the forward bias voltage of 0.6V at 25ᵒ (5)

3 9 i)explain the effect of temperature of a diode (5) ii) Derive the expression for transition and diffusion capacitance (8) 10 A germanium diode has a contact potential of.2volt while the concentration of accepted impurity atoms is 3x10^20/m^3. Calculate for a reverse bias of.1 volt, the width of the depletion region. If the reverse bias is increased to 10volt, calculate the new width of the depletion region. Assuming cross sectional area of the junction as 1mm^2, Calculate the transition capacitance values for both the cases. Assume Ɛr=16 for germanium (13) 11 i)examine the construction and working of Zener diode with a neat sketch ii) Compare HWR with FWR (7+6) 12 i)draw the expression for drift current density (5) ii)estimate the ideal reverse saturation current density in a silicon PN junction at T=300K, Consider the following parameters in the silicon pn junction. N d =N a = 10^16cm^-3, n i = ^10 cm^-3, D n =25 cm 2 /s, T p0 = T n0 =5 10^-7 s, D p =10cm 2 /s, Ɛ r =11.7.Comment on the result. (8) 13 i) In an N type semiconductor, the Fermi level lies 0.3 ev below the conduction band at 27ᵒC. If the temperature is increased to 55ᵒC, find the new position of the Fermi level. (7) ii) A PN junction diode has at a temperature of 125ᵒC, a reverse saturation current of 30μA. Find the dynamic resistance for 0.2V bias in forward and reverse direction. (6) 14 Illustrate the circuit diagram and explain the operation of full wave rectifier using center tap transformer and using bridge rectifier without center tap transformer. Obtain the expression for peak inverse voltage. (13) PART C 1. An AC supply of 220V, 50 Hz is applied to a HWR through a transformer of turn ratio 10:1. Deterrmine (i) Maximum RMS load Voltage (ii) Maximum RMS load current (iii) Power delivered to the load (iv) AC power input (v) Efficiency and ripple factor (vi) PIV, ripple frequency, ripple voltage and ripple current. (15) 2. A 230 V,50 Hz voltage is applied to the primary of a 5:1 stepdown centertapped transformer used in a FWR having a load of 900Ω. If the diode resistance and the secondary coil resistance together has a resistance of 100Ω determine, (i) DC voltage across the load (ii) DC current flowing through the load (iii) DC power delivered to the load (iv) PIV across each diode (v) Ripple voltage and its frequency (15) BTL2 BTL6 BTL2 UNIT II- TRANSISTORS BJT, JFET, MOSFET- structure, operation, characteristics and Biasing UJT, Thyristor and IGBT - Structure and characteristics. PART A

4 Q.No Questions BT Level Domain 1. What is base width modulation? 2. Name the two types of thyrister? 3. Solve I c and I E for a transistor that has α dc = 0.99and I B = 150μA. Determine the BTL 3 value of β dc for the transistor. 4. Show how an SCR can be triggered on by the application of a pulse to gate terminal 5. Inspect why it is necessary to stabilize the operating point of transistor. BTL 4 6. Compare BJT and FET. 7. Make use of the values of transistor has β=150, find the collector and base BTL 3 current if I E = 10mA 8. Identify some applications of JFET. BTL 3 9. How does a transistor act as a switch? 10. Examine thermal runaway in transistors? BTL Why FET is more temperature stable compared to BJT? 12. Formulate the relation between α dc and β dc? BTL what is meant by biasing a transistor? 14. Contrast BJT and JFET 15. Discuss the advantages of FET over BJT BTL Define amplification factor of JFET 17. Explain the intrinsic standoff ratio of a UJT? 18. Distinguish the latching current & holding current? BTL A BJT has a base current of 200μA. Determine the collector current and β. 20. In a n channel JFET I DSS =20 ma and V P = -6V. Estimate the drain current when V GS = -3V. PART B 1. With the help of suitable diagram, explain the working of enhancement MOSFET (13) 2. Describe the construction and working of UJT with it s equivalent circuit and VI characteristics. (13) 3. Elaborate the construction and operation of NPN transistor with neat sketch. Also comment on the characteristics of NPN transistor (13) BTL 3 BTL 6 4. With neat sketch, illustrate the construction, operation and characteristics of

5 SCR. (13) 5. i) Enumerate the selection of Q point for transistor bias circuit and discuss the limitations on the output voltage swing (8) ii) Show the cross section diagram of an N type enhancement mode MOSFET. Briefly explain its operation (5) 6. i) Demonstrate the basic construction and equivalent circuit of a UJT. Briefly explain the device operation (7) ii) Show the four layer construction of SCR and two transistor equivalent circuit. Explain the device operation (6) 7. Explain the following and derive the stability factor for each case. a. Fixed bias b. Collector to base bias c. Voltage divider bias. (4+4+5) 8. i) The reverse leakage current of the transistor when connected in CB configuration is 0.2 ma and it is 18 μa when the same transistor is connected in CE configuration. Determine α dc &β dc of the transistor. Assume I B =30mA. (8) ii) Distinguish between h-parameter and hybrid π model. (5) 9. Outline the construction of N channel JFET and also explain the drain and transfer characteristics of the same (13) 10. i) Recall the comparisons between CE, CB and CC configurations. (5) ii) What are the different compensation techniques used in BJT (8) BTL i) What is early effect describe with relevant expressions and figure (6) ii) Explain the construction and working of Ebers Moll transistor model (7) 12. i) Explain the structure and operation of Insulated Gate Bipoar Transistor. (8) ii) Distinguish MOSFET and IGBT (5) 13. i) Examine the various current components in a transistor. (8) ii) Explain the performance of FET as a voltage regulator.. (8) 14. Take part in discussion of the two transistor model of a thyristor in detail.(13)

PART C 1. Draw d.c load line for the following transistor configuration. Obtain the Quiescent point (15) BTL5 2. For the circuit shown below calculate V G, I D, V GS and V DS.

6 PART C 1. Draw d.c load line for the following transistor configuration. Obtain the Quiescent point (15) BTL5 2. For the circuit shown below calculate V G, I D, V GS and V DS. (15) BTL6 UNIT-III: AMPLIFIERS BJT small signal model Analysis of CE, CB, CC amplifiers- Gain and frequency response MOSFET small signal model Analysis of CS and Source follower Gain and frequency response-high frequency analysis PART A Q.No Questions BT Level Domain 1. Show the hybrid model of BJT in CE configuration 2. What are amplifiers? Write it s uses?

7 3. Model the small signal equivalent circuit of a CS JFET BTL 3 4. Justify the need of coupling capacitors in amplifier design? BTL5 5. Explain the four h-parameters BTL 4 6. For an amplifier, midband gain =100 and lower cut-off frequency is 1 khz. BTL 6 Estimate the gain of an amplifier at frequency of 20Hz. 7. Explain the significance of coupling and bypass capacitor on BW of amplifiers 8. Explain the term bandwidth and gain bandwidth product. BTL5 9. How can a DC equivalent circuit of an amplifier be obtained? 10. List out the different analysis available to analyze a transistor?. 11. Point out why CE configuration is preferred over CB configuration. BTL Outline the procedure to draw the a.c. equivalent of a network 13. Identify the reason for fall in gain at low and high frequencies BTL When transistor acts as a switch, in which regions of output characteristics it is operated. 15. Discuss about thermal runaway and how it could be avoided. BTL Develop the expression for pinch off voltage with respect to JFET. BTL When V GS of the FEET changes from -3.1V to 3V the drain voltage changes BTL 4 from 1 ma to 1.3mA Calculate the value of transconductance. 18. Define desensitivity. 19. Show the frequency response curve of an amplifier and what is 3 db frequency. 20. Compare the performance of CE,CB,CC amplifier configurations PART B 1. Illustrate the h-parameter model of a BJT-CE amplifier and derive the equations for voltage gain, current gain, input impedance and output impedance (13) 2. Describe about small signal MOSFET amplifiers (NMOS) and obtain the expression for it s trans conductance. (13) 3. Develop the h parameter equivalent circuit for a typical common emitter amplifier and derive the expression for Ai, Ri, Av and Ro. (13) BTL3 4. i)derive the expression for the voltage gain of CS amplifier (5) ii)for CS amplifier, the operating point is defined by V GSQ =-2.5V,V p = -6V and I dq =2.5mA with I DSS =8mA. Also R G =1MΩ, R S =1 KΩ, R D =2.2KΩ and VDD=15V.Calculate gm, rd, Zi, Zo and Av (8) 5. i)discuss the factors involved in Ic, Rc and Re for a single stage common emitter BJT amplifier circuit, using voltage divider bias (5) ii) A CC amplifier shown in below figure has V CC =15 V, R B =75kΩ and BTL3 BTL6

8 R E =910Ω The β of the silicon transistor is 100 and the load resistor is 600Ω. Estimate rin and Av (8) 6. The MOSFET shown in below figure has the following parameters. VT=2V, β= , rd=75kω. It is biased at ID=1.93 ma. Determine the impedance and voltage gain (8) With neat circuit diagram, evaluate the ac analysis for common source using equivalent circuit NMOSFET amplifier (5) Take part in the discussion on CB amplifier and derive the expression for h 7 parameters of the same. Also derive the expression for gain, input impedance and output impedance of CB amplifier. (13) 7. Explain about CS amplifier and derive the expression for gain, input impedance and output impedance and also draw its small signal equivalent circuit (13) 8. The hybrid parameters of a transistor used as an amplifier in the CE configuration arehie = 800Ω, hfe = 46, hoe = 80 x 10-6 and hre = 5.4x If R L = 5K and R s =500Ω. Find Ai, Ri, Av, Pi. (13) 9. Inspect the high frequency response of FET and derive the expression for lower cut off frequency and upper cut off frequency (13) 10 Demonstrate the low frequency analysis of BJT and also determine the effect of Cs, Cc & Cc on the low frequency response of BJT (13) 11 Explain about CC amplifier and derive the expression for h parameters of the same. Also derive the expression for gain, input impedance and output impedance of CC amplifier. (13) EC 6202 Electronic Devices And Circuits ( ) Odd semester.

(5) 13 i)show the low frequency h-equivalent model of a transistor amplifier operating in CE mode ii) Why is this circuit not valid for high frequencies iii) Define the trans conductance of BJT in

9 12 What are the factors affect the bias stability of a transistor? (8) Define the stability factors with respect to the changes in ICO,VBE and β. Why is the stability with respect to VCE not considered? (5) 13 i)show the low frequency h-equivalent model of a transistor amplifier operating in CE mode ii) Why is this circuit not valid for high frequencies iii) Define the trans conductance of BJT in the CE mode. How it is related to h parameters. (13) PART C 1. Acommon collector circuit has the following components; R 1 =21KΩ. R 2 = 27KΩ, R E =5.6 KΩ, R L =47KΩ, R S =600Ω. The transistors parameters are h ie =1KΩ, h fe =85 and h oe =2µA/V, Calculate A i, R i, A v, R o, A vs and A i =I O /I S (15) BTL5 2. A common base amplifier as shown in figure has the following components; R S =600, R C =5.6K, R E =5.6K, RL=K. The transistor parameters are h ie =1K, h fe =85 and h oe =2µA/V, Calculate A i, R i, A v, R o, A vs and A i. (15) BTL6

10 UNIT-IV: MULTISTAGE AMPLIFIERS AND DIFFERENTIAL AMPLIFIER BIMOS cascade amplifier, Differential amplifier Common mode and Difference mode analysis FET input stages Single tuned amplifiers Gain and frequency response Neutralization methods, power amplifiers Types (Qualitative analysis). PART A Q.No Questions BT Level Domain 1. What are cascaded amplifiers? 2. Model the ideal tuned circuits and write the expression for it s resonant BTL 3 frequency. 3. Explain how the differential amplifier can be used as an emitter coupled phase BTL 4 inverter 4. Elaborate the need for neutralization? BTL 6 5. Identify the need for cascading the amplifiers BTL 3 6. What is CMRR? Examine various methods of improving CMRR. BTL 4 7. Recall the applications of differential amplifier? 8. Why neutralization is important? And give its types. 9. Construct a Differential amplifier and what is the ideal value of CMRR? BTL Distinguish common mode and difference mode? BTL Summarize the Advantages and performance of class-c amplifier 12. Explainthe term cross over distortion? BTL Illustrate the ideal tuned circuit and write the expression for it s resonant frequency? 14. State Miller s theorem 15. Explain the bootstrapping technique? BTL5 16. Compare the performance of various power amplifier types. 17. Discuss need of Complementary symmetry amplifiers? BTL Tell the advantages of Push pull amplifier 19. Enumerate the advantages of single tuned amplifiers. 20. Outline the need for constant current source for difference amplifier. PART B

11 1. Illustrate the circuit of emitter coupled BJT differential amplifier, and derive expressions for differential gain, common mode gain and CMRR. (13) 2 What is Neutralization? Explain any one method in brief? (13) 3. With neat sketch explain two stage cascaded amplifier and derive its overall Av, AI,RI and Ro (13) 4. Show the differential amplifier and its ac equivalent circuit. Derive for Ad and Ac. (13) 5. With neat sketch, explain the BJT differential amplifier with active load and derive Ad, Ac and CMRR. How CMRR can be improved (13) 6. Explain the different types of neutralization technique used in tuning amplifier (13) 7. Develop the equation for differential mode gain and common mode gain of a differential amplifier. (7+6) 8. The differential amplifier has the following values RC = 50 K, Re = 100K and Rs = 10K. The transistor parameters are rπ = 50K= h ie, h fe = Vo = 2 x10^3, r o = 400K.Determine Ad, Ac and CMRR in db. (13) 9. i)discuss the complementary symmetry class B amplifier and obtain its efficiency (7) ii) Elaborate the operation of class AB amplifier to avoid cross over distortion (6) 10. The dual input balanced output differential amplifier having R s =100Ω, R C =4.7KΩ, R E =6.8KΩ,h fe =100,VCC=+15V, VEE=-15V. Find operating point values, differential &common mode gain, CMRR and outputif V s1 =70mV(pp)at 1 khz and V s2 =40mV(p-p) (13) 11. A Class C amplifier with VCC=25V has RL=680Ω,Cp=4300pF,Lp=20μH and Rw=0.06Ω.The transistor has VCE(sat)=0.6V.Calculate the appropriate signal frequency, the output power and circuit efficiency. (13) BTL 3 BTL 3 BTL 6 BTL i) Draw a circuit diagram to show how the current in the output transistors of a power amplifier can be limited to a desired maximum level. Examine the circuit BTL 4 operation. (8) ii) Compare MOSFET to power BJT (5) 13. Classify the power amplifiers and calculate the efficiency each types? (13) 14. Explain about Class A transformer coupled amplifier and derive the expression for efficiency of the same. (13) BTL 4

5mA (iv) Efficiency if the current drain is 0.4mA and the output voltage is 30V PP. (v) Bandwidth of amplifier if Q=125 (vi) Worst case transistor power dissipation.

12 PART C 1. Figure shows dual input, balanced output differential amplifier configuration. Assuming silicon transistors with h ie =2.5KΩ. (15) BTL 6 2. For the circuit shown below, calculate (i) Output power if the output voltage is 50 V PP (ii) Maximum ac output power (iii) DC input power if current drain is 0.5mA (iv) Efficiency if the current drain is 0.4mA and the output voltage is 30V PP. (v) Bandwidth of amplifier if Q=125 (vi) Worst case transistor power dissipation. (15) UNIT-V: FEEDBACK AMPLIFIERS AND OSCILLATORS Advantages of negative feedback voltage / current, series, Shunt feedback positive feedback Condition for oscillations, phase shift Wien bridge, Hartley, Colpitts and Crystal oscillators. PART A

13 Q.No Questions BT Level Competence 1. Tell the disadvantages of negative feedback in amplifiers and how it can be overcome? 2. Show the expression for the frequency of oscillations of a wein bridge oscillator? 3. Summarize the advantages of negative feedback circuits. 4. What is the advantage of a Colpitts oscillator compared to a phase shift oscillator? 5. Which is the most commonly used feedback arrangement in cascaded amplifier and why? 6. Recall the Barkhausan criterion for an oscillator. 7. Identify the difference between an oscillator and amplifier? BTL 3 8. Name two high frequency oscillators. 9. Outline the advantages of crystal oscillator? 10. Discuss about Nyquest s stability criteria for feedback amplifiers BTL Develop the oscillator model uses both positive and negative feedback? Why? BTL Determine the operating frequency of transistor Hartley oscillator if L1=50μH, BTL5 L2=1mH, and mutual inductance between the coils M=10 μh and C=10pF. 13. List the five characteristics of an amplifier which are modified by negative feedback. 14. Elaborate on Piezo electric effect. BTL List out the advantages of crystal oscillator? 16. Examine the effects on bandwidth and output impedance due to various types of feedback. 17. Illustrate the expression for frequency of oscillation of a Wein bridge oscillator 18. Distinguish the negative and positive feedback? 19. Identify the limitations of LC and RC oscillators BTL3 20. A wein bridge oscillator is used for operate at f o =10KHz. If the value of R is 100Ω. Estimate the value of capacitor. PART-B 1. Illustrate the circuit of CE amplifier with current series feedback and obtain the expression for feedback ratio, voltage gain, input and output resistances. (13) 2 Explain the operation of Colpitts Oscillator with neat circuit diagram. Also derive the expressions for the frequency of oscillation and the condition for maintenance of oscillation. (13) 3. Calculate Rif, Rof, Av and Avf for the following (i) Voltage hunt feedback amplifier (ii) Current series feedback amplifier (7+6) BTL 4

14 4. Outline the following with neat diagram. (i) RC phase shift oscillator. (ii) Hartley oscillator. (7+6) 5 Make use of a circuit diagram explain the operation of the following oscillators. (i) Wein bridge oscillator (5) (ii) Design a Wein bridge oscillator circuit to oscillate at a frequency of 20 khz. (4) (iii) Crystal oscillator. (5) BTL 3 6 Sketch a circuit diagram of a two stage capacitor coupled BJT amplifier that uses series voltage negative feedback. Describe how the feedback operates. (13) 7 Show the circuit diagram explain the operation of an RC phase shift oscillator and derive the condition for oscillation and resonant frequency with BJT. (13) 8 Take part in the discussion of the four types of topology for feedback of an amplifier. Derive the expression for gain with feedback. Mention the advantages of negative feedback amplifier. (13) 9 Design a Colpitts oscillator with C 1 = 100pf and C 2 = 7500pf. The inductance is variable. Determine the range of inductance values, if the frequency of oscillation is to vary between 950 KHz and 2050 KHz. (13) 10 A Hartley oscillator is designed with L1 = 2mH, L2 = 20μH and a variable capacitance. Find the range of capacitance value if the frequency of oscillation is varied between 950 to 2050 KHZ (13) 11 Explain the general characteristics of a negative feedback amplifier. Represent voltage series, voltage shunt, current series and current shunt. (13) 12 What is the condition for oscillation of a Hartley oscillator. Briefly explain the operation and derive the equation for f r and h fe. (13) 13 Two identical amplifier stages, each with voltage gain of 20dB and B.W of 25kHz are cascaded. To improve gain stability the cascade is provided with negative feedback to the extent of 10%. Estimate the effective gain and bandwidth. (13) 14 With a neat circuit diagram, describe the working of a Wien bridge oscillator. Derive an expression for the resonant frequency. Give its advantages and disadvantages? (13) BTL 4 BTL6 BTL 4 BTL 3 PART C 1. An amplifier has a mid frequency gain of 100 and a bandwidth of 200 khz. a) What will be the new bandwidth and gain if 5% negative feedback is introduced.

15 (b) What should be the amount of feedback, if the bandwidth is restricted to 1 MHz. 2. The frequency of oscillation of a Colpitts oscillator is given by F 0 = ( ) Where L,C 1 and C 2 are the frequency determining components. Such a circuit operates at 450kHz with C 1 = C 2.What will be the oscillation frequency if the value of C2 is doubled. BTL 6

VALLIAMMAI ENGINEERING COLLEGE

VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur 603 203 DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING QUESTION BANK III SEMESTER EC6202 - Electronic Devices and Circuits Regulation 2013