ece-1109 ECE-1109 Introduction to ECE
I. FUNDAMENTALS OF SOLID STATE & MATERIALS
I.A. Electron Theory & Conductivity
| Question Text | Years of Appearance |
| What are the main drawbacks of classical free electron theory? Explain the assumptions made in quantum theory to overcome the drawbacks. | 2016, 2018 |
| What are the main drawbacks of classical free electron theory? Illustrate why and how the resistivity varies with temperature and composition of metals. | 2015 |
| Explain the free electron theory of electrical conductivity in metals. Hence provesigma=fracne2taum, where the symbols have their usual meanings. | 2015, 2017, 2021 |
| Derive the expression for the electrical conductivity of metal from the microscopic point of view. | 2016 |
| Explain the electron scattering mechanism in metals. Explain also why and how the conductivity varies with temperature and composition. | 2015, 2016, 2017, 2020 |
| Conductors have a positive temperature coefficient whereas semiconductor materials have a negative temperature coefficient - why? Explain briefly. | 2016, 2018, 2021 |
| Explain the negative temperature co-efficient of semiconductor. Illustrate the junction temperature effect with proper diagram. | 2020, 2021 |
| State Matthiessen’s rule for the resistivity of metals. Show that the temperature dependence of resistivity of metal isrho=rho_T+alphaT. | 2018 |
| Write down Matthiessen’s rule. Show that resistivity of conductor is changed with temperature. | 2019 |
| What are the main sources of electrical resistance in metal? Discuss the effect of impurity, temperature and alloying on electrical resistivity of metal. | 2021 |
I.B. Band Structure, Fermi Level & Carriers
| Question Text | Years of Appearance |
| What is Electronic Band Structure? Draw the energy bands of Conductors, Semiconductors and Insulators. | 2018, 2019, 2021, 2024 |
| Briefly explain the formation of energy band in a solid. Classify the solids according to energy band structure. | 2023 |
| Briefly explain the formation of forming stable bond in solid and hence find out the expression of equilibrium spacing between atoms. | 2017 |
| What is the physical meaning of energy profile? How can you find potential diagram or bond diagram? Explain with an example. | 2015 |
| What is Fermi level? How the Fermi level is changed with the increase in temperature? Is it the same for intrinsic and extrinsic semiconductors? | 2019, 2021 |
| What is Fermi-Dirac function? Graphically show its variation with temperature. | 2020 |
| Show that the Fermi level in an n-type semiconductor is E_F=E_c−KTlnfracN_cN_D, where the symbols have usual meaning. | 2019 |
| What is meant by intrinsic and extrinsic semiconductors? Illustrate the variation of carrier concentration of a semiconductor with the change in temperature. | 2023 |
| Describe the temperature dependence of both gap energy and carrier concentration in case of both intrinsic and extrinsic semiconductor. | 2017 |
| Describe the temperature dependence of the electron concentration in an n-type semiconductor. | 2015 |
| Explain the current conduction mechanism in a semiconductor material. | 2017 |
| Briefly explain the electron hole flow mechanism within a semiconductor. | 2017 |
| Describe the effect of impurity on the energy of a semiconductor. | 2019 |
| What is thermally generated charge carriers? Write and explain ‘Wiedemann-Franz Law’. | 2019 |
| Define “Electron emission”. Explain secondary and field electron emissions with necessary diagrams. | 2019 |
| Define electron emission. Write down the process of thermionic emission with necessary diagrams. | 2021 |
| Define ‘work function’ and ‘surface-barrier’. Explain ‘Thermionic’ and ‘Photo-electric’ electron emissions. | 2018 |
| What is a crystalline solid? Why the semiconductor crystals are of natural choice for electronic devices? | 2015 |
| Justify the statement-”n-type or p-type semiconductor is electrically neutral.” | 2016, 2017, 2022 |
| Why is silicon preferred to Germanium in manufacturing semiconductor devices? | 2023 |
I.C. Diffusion, Continuity & Hall Effect
| Question Text | Years of Appearance |
| Derive the continuity equation of charge in semiconductor. Also explain its physical significance. | 2016, 2019, 2021 |
| Write down the physical significance of continuity equation. Using this equation, show that the diffusion length for holes is L_p=sqrtD_ptau_p, where the symbols have their usual meanings. | 2017 |
| When the concentration of carriers are more than the equilibrium values, what happens? Derive the mathematical expression for the rate of change of electron concentration where the diffusion from the equilibrium values is small. | 2015 |
| Briefly describe the phenomena of Hall effect. Write down few applications of it. | 2016, 2017, 2021 |
| Describe Hall effect with necessary diagram. Write down the importance and application of Hall effect. | 2019 |
| What is skin effect? Write down the importance and applications of Hall effect. | 2018 |
I.D. Calculations (Materials)
| Question Text | Years of Appearance |
| For a particular semiconductor material, N_c=1.5times1018textcm−3**,** N_v=1.3times1019textcm−3 and E_g=1.43texteV at T=300^\\circ \\text{K}. (i) Determine the position of the intrinsic Fermi level… (ii) Find the intrinsic carrier concentration… | 2016, 2017, 2018, 2020 |
| For a silicon conductor, the diffusion constant is 13textcm2/textsec. For room temperature (30^\\circ \\text{C}), Find out the mobility of charge carriers. Also find out the mean scattering time ‘tau’ from that value. | 2018 |
| A conductor has diffusion constant of 13.7textcm2/textsec, for temperature at 31^\\circ \\text{C}, find out the mobility of the charge carriers. | 2019 |
| Find the resistance of a 1textcm3 pure silicon crystal… | 2015 |
| Calculate the mean scattering time of conduction electrons in copper… | 2019 |
| An electric field of 2.3times105textVm−1 is applied to a copper wire… Calculate (i) Resistivity and mobility of the conductor. (ii) The current through the conductor. (iii) What is the length of the wire? | 2018 |
| A uniform silver wire has a resistivity of 1.54times10−8Omegacdottextm at room temperature… calculate the average drift velocity of electron… Also calculate the mobility. | 2021 |
| A tungsten filament consists of a cylindrical cathode… find the emission current. | 2019 |
| What is the critical electric field that will impose a drift velocity equal to 0.1 of mean speed… Determine the current density and current through a copper wire… | 2020 |
II. P-N JUNCTION DIODES
II.A. Formation, Width, and Potential
| Question Text | Years of Appearance |
| Explain the formation of depletion layer in p-n junction. How the width of the depletion layer is changed with doping level? | 2015, 2016, 2018, 2019, 2020, 2021, 2022 |
| Show that contact potential of p-n junction is V_0=KTlnfracN_DN_An_i2**, where the symbols have their usual meanings.** | 2015, 2016, 2018, 2020 |
| Show that the width of the space charge region at a p-n junction is W=sqrtfrac2epsilonV_0q(frac1N_d+frac1N_a), where the symbols have their usual meanings. | 2017, 2018, 2021 |
| When a p-n junction is at equilibrium, there is a contact potential. Explain how the contact potential is needed to maintain the equilibrium condition. What is the origin of the contact potential? | 2024 |
| What is barrier potential? How can it be overcome in p-n junction? Explain with necessary diagrams. | 2019 |
II.B. Characteristics and Operation
| Question Text | Years of Appearance |
| Draw a schematic diagram showing the energy band of a p-n junction when it is forward biased. Show clearly the positions of the Fermi levels on two sides of the junction. Explain how the carrier and current flow is affected by a forward-biased voltage. | 2016, 2017, 2022, 2024 |
| Establish the relation I=I_0(eV/etaV_T−1) for a p-n junction diode, where the symbols have their usual meanings. | 2015, 2016 |
| Show that the dynamic resistance of a diode is r=fracetaV_TI, where the symbols have their usual meanings. | 2023 |
| Draw the V/I characteristic curve of a p-n junction and show the procedure to calculate the forward ac resistance. | 2024 |
| With the help of suitable diagram, illustrate the current components in a p-n diode. | 2016, 2022 |
| Prove that the current passing through a diode in forward bias condition is a summation of majority and minority carriers flow. | 2019 |
| Explain the operation of a semiconductor diode for the given conditions - (i) No bias, (ii) forward bias, and (iii) reverse bias. Also, draw the characteristics curve of a silicon diode. | 2023 |
| Draw and explain the diode equivalent circuits and characteristic curve for: (i) Piecewise-linear model (ii) Simplified model (iii) Ideal device. | 2017 |
| With a neat sketch, explain the load line and the Q-point for a diode circuit. | 2015, 2021 |
| Draw and explain the application of diode circuit for logical AND operation. | 2022 |
| Draw and explain the application of diode circuit for logical OR operation. | 2024 |
| Explain that an ideal diode acts as a switch. | 2022 |
| How can a junction diode be called as a switch? | 2017 |
| How can a junction diode be used as a protection element for LED? | 2018, 2023 |
| What is leakage current? Write down the applications of liquid crystals. | 2019 |
II.C. Breakdown and Switching
| Question Text | Years of Appearance |
| Briefly describe the process of ‘Avalanche’ and ‘Zener’ breakdowns. | 2015, 2017, 2018, 2021, 2024 |
| What do you mean by breakdown of a p-n junction? Briefly describe the avalanche and zener breakdown mechanism. | 2022 |
| What is minority carrier storage time of a diode? How does it limit the performance of a switching diode? Explain. | 2015, 2016, 2017 (Q3c & Q4a), 2023 |
| What is minority carrier storage time of a diode? How does it limit the performance of a switching diode? Explain in brief. | 2016 |
| How does transition capacitance form in a p-n junction. Explain with necessary diagrams. | 2021 |
| Write short notes on “Transition capacitance” and “Diffusion capacitance”. | 2019 |
| How does capacitance formed in a p-n junction? Find an expression for the diffusion capacitance of an ideal p-n junction diode in which the doping concentration of the p-side is very high than that on n-side. | 2015, 2016 |
II.D. Diode Calculations & Analysis
| Question Text | Years of Appearance |
| A Si p-n junction with cross-sectional area A=0.001textcm2… Calculate: i. Contact potential V_0. ii. Current with a forward bias of 0.5textV… iii. Current at reverse bias of −0.5textV. | 2015 |
| A Si p-n junction with cross sectional area A=10−2textcm2… Calculate: (i) Contact potential V_0. (ii) Current with forward bias of 0.5textV… (iii) Current at reverse bias of −0.5textV. | 2017 |
| A Si p-n junction with cross sectional area A=10−2textcm2… Calculate: (i) Contact potential V_0. (ii) Current with forward bias of 0.4textV… (iii) Current at reverse bias of −0.5textV. | 2020 |
| Consider a silicon p-n junction at room temperature doped at N_A=1014textcm−3 in the p-region and N_D=1017textcm−3 in the n-region… Calculate the contact potential of the p-n junction. | 2021 |
| A surge bias is applied to the germanium p-n junction diode… What will be the current at room temperature when the forward bias is 0.15textV. | 2021 |
| The resistivity of the two sides of an abrupt germanium diode are 2.0Omegacdottextcm (p side) and 10Omegacdottextcm (n side) at 300^\\circ \\text{K}. Calculate the height E_0 of the potential energy barrier. | 2016 |
| Determine V_0 and I_0 for the configuration of Figure 5(c). | 2015, 2019 |
| Determine V_0 and I_0 for the configuration of figure 6(a). | 2016 |
| Determine V_0 and I_0 for the configuration of Fig. 6(c). | 2020 |
| Determine the currents I_1 and I_2 for the network of Figure 1(d)… | 2022 |
| Calculate the current through 1textKOmega resistor(s) and draw the voltage V_0 with proper labeling for the following circuit. | 2017, 2020, 2024 |
| Sketch the output V_0 and determine the dc level of the output for the network of figure 6(d). (ii) Repeat part (i) if the ideal diode is replaced by a silicon diode. | 2016 |
| Find out the operating point and calculate the voltage across the load from figure 5(d). | 2016, 2018 |
III. TRANSISTORS (BJT & FET)
III.A. BJT Fundamentals and Equations
| Question Text | Years of Appearance |
| Prove that the expression for collector current of common base connection is I_c=fracalpha1−alphaI_B+fracI_CB01−alpha**, where the symbols have their usual meanings.** | 2015, 2016, 2017, 2018, 2022, 2023 |
| Find the relationship betweenalpha andbeta of BJT, where the symbols have their usual meaning. | 2021, 2024 |
| Write down the advantages of transistor over vacuum diode. “Emitter of a transistor is doped heavily but base is lightly doped” - why it is so? | 2019 |
| Show that the common emitter configuration, collector current is not zero, even if the base current is zero. | 2019, 2021 |
| Explain the amplification action of a transistor with proper example. | 2017, 2019 |
| Explain the input and output characteristics of common emitter configuration with appropriate figure. Write the comparison among common emitter, base collector configuration. | 2021, 2024 |
| Explain the output characteristics of common emitter configuration with appropriate figure. | 2022 |
III.B. BJT vs FET and JFET
| Question Text | Years of Appearance |
| What are the differences between BJT and FET? Mention the advantages of FET over BJT. | 2015, 2018, 2022, 2024 |
| What are the differences between BJT and FET? | 2017 |
| Write down the difference between BJT and FET with proper symbols. | 2019 |
| Define the following terms: (i) Pinch off voltage (V_P), and (ii) Gate-Source cut off voltage (V_GS(off)). | 2015, 2021, 2024 |
| Define Pinch off voltage? Explain the working principle and output characteristics and symbols of P-channel JFET. | 2024 |
| For N-Channel JFET, why the depletion region is wider near the top of the p-type materials. Explain briefly. | 2015, 2016 |
| How can you use JFET as a constant current source? Briefly explain with necessary diagram. | 2015, 2016, 2017 |
| Define channel formation and explain the output characteristics of n-channel JFET. Derive the relationship between I_D and V_GS. | 2022 |
| Explain the working principle and output characteristics of p-channel JFET. Derive the relationship between I_D and V_GS. | 2023 |
| Explain the transfer characteristics of JFET. Describe the operation of p-channel enhancement type MOSFET with appropriate figure. | 2019 |
III.C. MOSFET
| Question Text | Years of Appearance |
| What is the primary difference between D-MOSFET and E-MOSFET? Explain the basic operation and characteristics of D-MOSFET. | 2015, 2016, 2018, 2022 |
| What is the primary difference between D-MOSFET and E-MOSFET? Describe the operation of p-channel depletion type MOSFET with appropriate figure. | 2024 |
| Explain the basic operation and characteristics of E-MOSFET with necessary sketch. | 2017 |
| Describe the operation of p-channel enhancement type MOSFET with appropriate figure. | 2020 |
| What is meant by channel enhancement in E-MOSFET? Explain the construction, basic operation, and characteristic of p-channel E-MOSFET. | 2023 |
| Write down the differences between BJT and JFET. Describe the operation of p-channel depletion type MOSFET with appropriate figure. | 2021 |
| Sketch the transfer characteristics for an n-channel depletion-type MOSFET with I_DSS=10textmA and V_P=−4textV. | 2022 |
III.D. Transistor Calculations & Analysis
| Question Text | Years of Appearance |
| Calculate the voltage gain A_v of Figure 8(d)… Assume amplification factoralpha_ac=1. | 2015, 2018, 2020 |
| Determinealpha_dc if I_c=2.8textmA and I_e=2.9textmA. | 2018 |
| A JFET has a drain current of 5textmA. If I_DSS=10textmA and V_GS(off)=−6textV, find the value of (i) V_GS and (ii) V_P. | 2019, 2021 |
| For the JFET in Fig. 6(b), V_GS(off)=−3textV and I_DSS=10textmA. Determine the minimum value of V_DD required to put the device in the constant current region of operation. | 2021 |
| Determine the state of the transistor (operating region) in the circuit shown in Fig. 4(d). | 2024 |
| Calculate the base, collector and emitter currents and the CE voltage for a common emitter circuit… | 2022 |
| In a common base configuration,alpha=0.96. The voltage drop across 2textKOmega resistance… Find (i) voltage drop across resistance 5textKOmega, (ii) base current, and (iii) base current configuration. | 2019 |
| Determine the value of drain current for the circuit shown in Fig. 8(d). | 2024 |
IV. SPECIALIZED DIODES & COMPONENTS
IV.A. Zener Diodes (Theory & Applications)
| Question Text | Years of Appearance |
| A zener diode is operated in the reverse breakdown region but it does not burn, why? | 2015, 2016, 2020, 2023 |
| What is Zener region? Explain the p-n junction for reverse bias condition. | 2019, 2022, 2024 |
| Determine the following relations for a zener diode with fixed V_i and variable R_L, where the symbols have their usual meanings. | 2016 |
| Determine the following relations for a zener diode with fixed V_i and variable R_L: (i) R_Lmin=fracRV_i−V_zV_z, (ii) R_Lmax=fracRV_zV_i−V_z(min). | 2017 |
IV.B. Specialized Diodes (Other)
| Question Text | Years of Appearance |
| Write short note on (i) Tunnel diode, (ii) Varactor diode. | 2016, 2017, 2022 |
| Write short notes on the following diodes: i. Tunnel diode, ii. LED. | 2015 |
| Write short notes on (i) Tunnel diode (ii) Photo Diode. | 2018 |
| What is tunneling effect? Explain the negative resistance region of a tunnel diode with appropriate application. | 2021, 2024 |
| What is varactor diode? Describe the operation of a voltage controlled tuning with varactor diode. | 2019, 2020, 2023 |
| What is varactor diode? Explain the voltage control tuning principle of varactor diode. | 2020 |
IV.C. Zener Calculations
| Question Text | Years of Appearance |
| Design a voltage regulator using a Zener diode that will remain an output voltage ofpm50textV**… find the maximum and minimum values of zener diode current.** | 2018 |
| A zener diode used in a voltage regulator remains an output voltage ofpm50textV**… then find out the range of input voltage that can be varied.** | 2019, 2021 |
| Design a voltage regulator using a Zener diode… Determine the maximum power rating of the Zener diode required to design the circuit. | 2015, 2023 |
| Determine the range values of V_i that will maintain the Zener diode of Figure 7(d) in ‘on’ state. | 2015, 2018 |
| The circuit of Figure 6(b1) is an inexpensive voltage regulator. All the diodes are ideal. Find the regulation of V_0… | 2017 |
| A zener diode has the specifications V_z=5.2textV and P_zmax=260textmW… Find the maximum allowable current I_L when the zener diode is acting as a regulator. | 2017 |
| Design a Zener diode voltage regulator using the circuit in Figure 3(d)… | 2022 |
| For the network of figure below, determine the range of V_i that will maintain V_L at 8textV and not exceed the maximum power rating of the Zener diode. | 2024 |
| For the Figure 6(a) [Zener regulator circuit], find the (i) voltage at point ‘a’, (ii) voltage across resistor R_r, (iii) voltage drop across resistor R, (iv) the current through zener diode… | 2019 |
| The circuit of Figure 6(d) uses two zener diodes… determine (i). the regulated output voltage, (ii) maximum load current, and (iii) minimum load current. | 2019 |
| In the circuit shown in Fig. 5(a), the Knee current of the zener diode is 10textmA… find the minimum value of R_L inOmega and the minimum power rating of the zener diode intextmW. | 2020 |
V. RECTIFIERS AND POWER SUPPLIES
V.A. Rectification and Efficiency
| Question Text | Years of Appearance |
| Show that in half-wave rectification, a maximum of 40.6% of ac power is converted into dc power. | 2016, 2018, 2020 |
| Show that the PIV for each diode is double in a full wave rectifier using center tapped transformer than that of a bridge rectifier. | 2016, 2018, 2021 |
| Write down the operation of a center-tap full wave rectifier. Show that for center tap rectifier, PIV=2V_m. | 2019 |
| Write down the advantages and disadvantages of center-tapped full wave rectifier. How can you eliminate those disadvantages? | 2016 |
| In the center tap circuit shown in figure 2(d)… Find (i) DC output voltage, (ii) Peak Inverse voltage (PIV), and (iii) Rectification efficiency. | 2015, 2023 |
| Figure (6c) shows the bridge type circuit… Find the dc voltage and PIV for dc output. Assume the diodes to be ideal. | 2018 |
| The bridge circuit shown in Figure 2(d) type circuit… Find (i) DC output voltage, (ii) Peak Inverse voltage, and (iii) Rectification efficiency. | 2022 |
| Can the transformer and load be interchanged in a bridge rectifier? Explain. | 2024 |
| A crystal diode having internal resistance r_f=10Omega is used for full wave bridge rectification… Find… | 2021, 2024 |
| A full wave bridge rectifier is used to supply 50textV dc… Calculate (i) ac voltage required at primary coil of a transformer, (ii) Efficiency of a transformer in terms of power, and (iii) Ripple factor in terms of current. Use the simplified model for diode. | 2020 |
V.B. Filters and Regulated Supplies
| Question Text | Years of Appearance |
| What is meant by regulated power supply? Design a regulated power supply for your mobile phone (+5V dc) from 220V ac mains. Mention the input and output wave shapes at every stages with proper labeling. | 2015, 2016, 2017, 2018, 2021 |
| Why are the filter circuits necessary in DC power supply? Mention different filters with their circuit diagrams. | 2017, 2024 |
| Why are the filter circuits necessary in DC power supply? Explain the operation ofpi-filter with suitable diagram. | 2015 |
| What do you mean by filter circuits? Explain the operation of api filter with appropriate diagram. | 2018, 2019 |
| Why are the filter circuits necessary in DC power supply? Show that the ripple voltage for an RC filter connected with full wave rectifier can be given by V_r=fracI_dc2fC… | 2022, 2023 |
| Design a “pi”-filter with appropriate biasing. How you can tune the degree filtering using this filter? | 2021 |
VII. GENERAL & COMMUNICATION/DIGITAL FUNDAMENTALS
| Question Text | Years of Appearance |
| What do you mean by Electronics? Write down the applications of Electronics. | 2018 |
| What are the differences between solid state and non-solid state components? Why do we need to study solid state physics? | 2018 |
| What are the differences between electronics devices and integrated circuit. | 2022 |
| Explain the evolution of integrated circuit (IC). List the applications of electronics in communication areas. | 2024 |
| What do you mean by dark current and dark resistance? | 2016 |
| All the signals need to be carried in electronic communication systems… [General Communication System components/theory] | 2023 |
| Draw and explain the construction of co-axial cable. Write the transmission characteristics of co-axial cable. | 2023 |
| Classify bandwidth. Explain the bandwidth requirements for different modulation schemes… | 2023 |
| What is optical fiber? Classify it according to the transmission characteristics. | 2023, 2024 |
| Explain exclusive AND De Morgan’s theorems of Boolean algebra. Design the exclusive-NOR gate using NAND as a universal gate. | 2023 |
| What are universal gates? Design an X-OR gate using NAND as a universal gate. | 2024 |
| Write short notes on - (i) CCITT, (ii) ITU-T, (iii) ITU-R, and (iv) ITU-D. | 2024 |
| Give the block diagram representation of a typical digital communication system. Also mention the advantages and disadvantages of digital communication over analog counterpart. | 2024 |
| Draw and explain the working principle of carbon microphone. List the disadvantages of carbon microphone. | 2023, 2024 |
| Assuming that the computer uses 8 bit 2’s complement arithmetic, show how it would compute (25−46)_10. | 2024 |