ee2203-electronic devices and...

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EE2203 – ELECTRONIC DEVICES AND CIRCUITS

QUESTION BANK WITH ANSWER

2 MARK & 16 MARK

UN IVERSITY QUESTION WITH ANSWER • NOV/DEC 2009 • MAY/JUNE 2010 • NOV/DEC 2011

PREPARED BY

S.MALARKODI, AP/EEE

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Syllabus EE2203 ELECTRONIC DEVICES AND CIRCUITS 3 0 0 3 AIM To study the characteristics and applications of electronic devices. OBJECTIVES To acquaint the students with construction, theory and characteristics of the following electronic devices:

i) p-n junction diode ii) Bipolar transistor iii) Field effect transistor iv) LED, LCD and other photo electronic devices v) Power control / regulator devices

1. PN DIODE AND ITS APPLICATIONS 9 PH junction diode-VI characteristics – Rd, temperature effects – Drift ad diffusion currents – switching – Rectifiers: HWR, FWR, BR, filters-Zener diode – VI characteristics, Regulators (series and shunt), LED, LCD characteristics and applications. 2. BJT AND ITS APPLICATIONS 9 Junction transistor – Transistor construction – Input and output characteristics – CE, CB and CC configurations – hybrid model – Analytical expressions – switching – RF application – Power transistors – Opto couplers. 3. FET AND ITS APPLICATIONS 9 FET – VI characteristics, VP, JFET – small signal model – LF and HF equivalent circuits – CS and CD amplifiers –cascade and cascade – Darlington connection – MOSFET - Characteristics – enhancement and depletion 4. AMPLIFIERS AND OSCILLATORS 9 Differential amplifiers: CM and DM – condition for ofc-feedback amplifiers – stability – Voltage / current, series / shunt feedback – oscillators – LC, RC, crystal 5. PULSE CIRCUITS 9

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RC wave shaping circuits – Diode clampers and clippers – Multivibrators – Schmitt triggers – UJT based saw tooth oscillators. TOTAL : 45 PERIODS TEXT BOOK 1.Paynter, “Introductory Electronic devices and circuits, 2006, PHI 2.David Bell “Electronic Devices and Circuits” 2007, PHI REFERENCES 1.Theodre F.Boghert, “Electronic Devices & Circuits” Pearson Education, VI Edition, 2003 2. Rashid, “Microelectronic circuits” Thomson Publication, 1999 3. B.P.Singh & Rekha Sing, “Electronic Devices and Integrated Circuits” Pearson Education, 2006.

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UNIT – I PN DIODES AND ITS APPLICATIONS

(2 Mark Question & Answers)

1. Write down & explain junction diode equation. The equation which explains the forward and reverse characteristics of a semiconductor diode is known as diode equation. The diode current is given by

V/η. VT I = Io (e - 1)

Where, Io- reverse saturation current η- Constant; 1-for Germanium diodes, 2- for silicon diodes V- External voltage, is positive for forward bias and negative for reverse bias. VT – Volt equivalent of temperature. (VT value is T/11,600) T – Absolute temperature. At room temperature(i.e.300K) VT is equal to 26 mV) 2. Define static & dynamic resistance.

• Static resistance is defined as the ratio of the voltage to current in forward bias characteristics.

• Dyanamic resistance is defined as the reciprocal of the slope of the volt ampere characteristics.

3. What is transition & diffusion capacitance?

• The capacitance that occurs in reverse bias junction is called as transition capacitance & is denoted as CT.

• The capacitance that occurs in forward bias junction is called as diffusion capacitance & is denoted as CD.

4. A Germanium diode has a saturation current of 10µA at 300oK .Find the

saturation current at 400oK.

I300=10µA T1=300K T2=400K

I400=I300*10-6*210 =10.2 mA

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5. Define & explain peak inverse voltage (PIV)

Peak inverse voltage is the maximum reverse voltage that can be applied to the PN junction without damaging the junction. If the reverse voltage across the junction exceeds to its peak inverse voltage, the junction may be destroyed due to excessive heat.

6. Explain the terms knee voltage and breakdown voltage with respect to diodes. Knee voltage : It is the forward voltage of a PN diode at which the current through the junction starts increasing rapidly after overcoming the potential barrier It is approximately equal to the barrier potential of the diode. Break down Voltage - It is the reverse voltage of a PN junction diode at which the Junction breaks down with sudden rise in the reverse current. 7. What is forward bias and reverse bias in a PN junction? Forward bias :

When positive terminal of the external supply is connected to P region and negative terminal to N region ,the PN junction is said to be forward biased. under forward biased condition the PN region offers a very low resistance and a large amount of current flows through it. Reverse bias:

When positive terminal of the external supply is connected to N region and negative terminal to P region ,the PN junction is said to be reverse biased. under reverse biased condition the PN region offers a very high resistance and a very small amount of current (µA)flows through it.

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8. Differentiate Drift current & Diffusion current

Drift current Diffusion current Movement of charge carriers due to application of electric field Phenomenon found both in semiconductors & metals

Movement of charge carriers due to concentration gradient Only in semiconductors

9. What is barrier potential? The electric field formed in the depletion region acts as a barrier. External energy must be applied to get the electrons to move across the barrier of the electric field. The potential difference required to move the electrons through the electric field is called the barrier potential. Barrier potential of a PN junction depends on the type of semiconductor material, amount of doping and temperature. This is approximately 0.7V for silicon and 0.3V for germanium. (Because of the oppositely charged ions present on both sides of PN junction an electric potential is established across the junction even without any external voltage source which is termed as barrier potential.)

10. Write short notes on Zener Breakdown

Zener Breakdown: Breaking of covalent bonds is due to intense electric field across narrow depletion region .This generates large number of free electrons to breakdown. This occur for zener diode with Vz less than 6V.The temperature coefficient is negative.

11. Write short notes on Avalanche Breakdown Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents to flow within materials which are otherwise good insulators. It is a type of electron avalanche. 12. Write down the applications of Zener diode.

• As voltage regulator. • As peak clippers. • For reshaping waveforms. • For meter protection against damage from accidental application of

excessive voltage.

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13. List the applications of LED?

i) Indicators and signs

ii) Lighting

iii) Energy consumption

iv) Economically sustainable

v) Light sources for machine vision systems

14. Draw the symbol and V-I characteristic curve for PN diode.

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15. How does the avalanche breakdown voltage vary with temperature? In lightly doped diode an increase in temperature increases the probability of collision of electrons and thus increases the depletion width. Thus the electrons and holes need a high voltage to cross the junction. Thus the avalanche voltage is increased with increased temperature 16. What are the advantages of full bridge rectifier? i) centre tapped transformer is not needed. ii) for the same secondary voltage, the output is doubled than that of the centre tap circuit 17. Draw the symbol and V-I characteristic curve for Zener diode. Symbol:

Characteristics curve:

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18. Differentiate full wave rectifier and full wave rectifier? i)The efficiency of full wave rectifier is double that of a half wave rectifier. ii)The ripple factor is large and frequency of voltage is low in a half wave rectifier,hence the waveform cannot be easily smoothes whereas in full wave rectifier ,the frequency is large therefore can be filtered easily with simple filtering circuits. 20. What are the two mechanisms of zener diode? i) Avalanche breakdown ii)Zener breakdown 21.Draw the half wave circuit with input and output waveforms.

22. What is rectifier and rectification? Rectifier: Rectifier is an electrical device which can change an a.c current to d.c current. Rectification: The process of changes ac to d.c is called rectification.

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23. Mention the applications of PN diode. i) Rectifiers in power supplies ii)switch in digital logic circuits used in computers iii )clamping network used as d.c restorer in TV receivers and voltage multipliers iv)Clipping circuits used aas wave shaping circuits used in computers,radars,radio and TV receivers v)demodulation (detector) circuits. 24. Define LCD? A thin film of LC fluid is sandwiched between two glass plates. The glass plates are coated with conductive transparent in the film formed of the desired alpha numeric image. LCD’s consume less power and have the shortest life. 25. What is half wave rectifier? In half wave rectification, either the positive or negative half of the AC wave is passed, while the other half is blocked. Because only one half of the input waveform reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be achieved with a single diode in a one-phase supply, or with three diodes in a three-phase supply.

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(16 Mark Questions))

1. i) Explain V-I characteristics of a PN junction diode and also explain the formation of potential barrier and depletion layer with no external voltage? (12)

i) Draw the V-I characteristics curve (2) ii) Brief explanation about operation held in forward and reverse bias (4)

iii)Explanation of PN junction(2) iv)Formation of the Depletion Region.(2) v) Barrier Potential(2)

(ii) Discuss about the temperature effects in PN diode (4) 2.i) Explain the operation of bridge rectifier with neat diagram and waveforms.(16)

• Draw the circuit diagram of bridge rectifier (2) • Draw & explain the input and output waveforms (2) • Average value of the output voltage, Vdc (2)

• Average value of the output current, Idc (2)

• Output dc power, Pdc (2)

• rms value of the output voltage, Vrms (2)

• Output ac power, Pac (2)

• Efficiency, η (2)

3. What is voltage regulator? Explain the working principle of any series regulator type with circuit diagram.(16)

i) Define voltage regulator (2) ii) Brief explanation about the working principle with circuit diagram(8) iii) Types and applications (6)

4. With neat circuit diagram explain the operation of a half wave rectifier with necessary waveforms? Also mention its applications.(16)

i) Draw the circuit diagram of full wave rectifier (4) ii) Brief explanation about the input and output waveforms (8) iii) Advantages over half wave rectifier (2)

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iv) Applications (2) 5. What is LED? How do they work? Explain briefly, mention some of its application.

a) symbol and its explanation(2) b)working principle (6) c) Application of LEDs fall into three major categories (8)

6. i) Explain the operation of zener diode with its characteristic curve.(8) i) Draw the symbol of zener diode (1) ii) Brief explanation about the operation held at first and third quadrant.(5) iii) reason for voltage regulator (2)

UNIT-II BJT AND ITS APPLICATIONS (2 Mark Question & Answers)

1. What are the types of BJT & give their symbolic representation? There are two types of BJTs namely, npn and pnp. Their symbolic representation is as follows. pnp transistor npn transistor E C E C B B 2. Why Base is lightly doped & width of the Collector large?

Base is lightly doped in order to have lesser recombination with holes for pnp transistor. Collector should have larger width to accommodate large number of holes, and to increase dissipation at collector junction.

3. What are the types of configuration ? The types of configuration are a) common base configuration b) common emitter configuration c) common collector configuration

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4. Define current gain β in CE configuration? Current gain of CE is defined as the ratio of change in collector current to change in base current. When collector -emitter voltage is kept constant.

β=(∆Ic/∆Ib) ; Vce Constant.

5. Among CE, CB and CC configurations which is most popular? Why? Among CB, CE and CC configurations the most popular type is CE configuration. The reasons are 1. high current gain(around 500) 2. Output to Input impedance ratio is moderate therefore easy coupling is possible between various transistor stages.

6. What is biasing?

To operate the transistor in the desired region it is necessary to provide sufficient voltages of correct polarity and magnitude to the two junctions of the transistor. This is known as biasing. 7. What do you understand by Q-point.? For proper operation of a transistor in any application, we set a fixed level of certain currents and voltages in a transistor. These values of currents and voltages define the point at which the transistor operates. This point is called operating point. It is also known as quiescent point or Q-point. Since the level of currents and voltages are fixed, therefore the operating point is also called d.c operating point.

8. Name the various types of biasing circuits for transistors?

• Fixed bias or base resistor method • Voltage Divider bias or Self bias • Biasing with feedback resistor.

9. What is the advantage of using emitter resistance in context of biasing? To improve the bias stability, emitter resistance is used in biasing circuits. 11. Define stability factor The stability factor may be defined as the rate of change of collector current with respect to the reverse saturation current keeping the common emitter current gain (β) and base current (IB) as constant.

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CO

C

dI

dIs =

12. What are the factors affecting stability of Q-point? The factors affecting the stability of Q- point are

• Inherent variations of transistor parameters (ICO, IB, β dc) • Variation in parameter values of transistors of same type

13. What do you mean by thermal runaway? The collector current for CE configuration is given by

CBOBC

III )1( ++= ββ

The flow of current in the circuit produces heat at the junctions. This heat increases the temperature at the junctions. The increase in collector current increases the power dissipated at the collector junction. This in turn increases the temperature of the junction and hence increases the collector current. The excess heat produced at the collector base junction may even burn and destroy the transistor. This situation is called thermal runaway.

14. Why do we choose q point at the center of the load line? The operating point of a transistor is kept fixed usually at the center of the

active region in order that the input signal is well amplified. If the point is fixed in the saturation region or the cut off region the positive and negative half cycle gets clipped off respectively. 15. When does a transistor act as a switch? The transistor acts as a switch when it is operated at either cutoff region or saturation region. 16. What is d.c load line? The d.c load line is defined as a line on the output characteristics of the transistor which gives the value of Ic & Vce corresponding to zero signal condition. 17. In a transistor operating in the active region although the collector junction is reverse biased, the collector current is quite large. Explain. Forward biasing the input side and reverse biasing the output side are the requirements of a transistor in the active region. The collector current is experimentally equal to the emitter current .Therefore the collector current will be large as emitter current is large on the other hand in CE operation Ib is multiplied by β hence we get large collector current.

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18. Why is the transistor called a current controlled device? The output characteristics of transistor depend on the input current. So the transistor is called a current controlled device. 19. List the advantages of transistor hybrid model. i) h-parameters are real numbers upto radio frequencies ii) they are easily to measure 20. What are applications of BJT? i) transistor bust the signal ii) transistor amplify the current or voltage iii) transistor use of switching purposes 21. Why are power transistor provided with heat sinks? A thermal heat sink is usually used to draw heat from the device via thermal conductor which expels the heat into the ambient air via thermal convection and heat radiation. 22. What is the early effect in CB configuration and give its consequences? An increase in magnitude of collector voltage increases the space charge width at the output junction. Due to this the effective base width (w) decreases and this phenomenon is known as early effect. Consequences the charge gradient is increased within the base and consequently the current due to minority charge carriers injected across the emitter junction increases. 23. Why we use h-parameters to describe a transistor? H-parameters (hybrid) are real numbers at audio frequencies, are easy to measure, can also be obtained from the transistor static characteristic curves and are convenient to use in circuit analysis and design. H-parameters are used to obtain transistor linear model. 24.Comparision of transistor connection. S.no Characteristics Commom base Common emitter Common

collector 1 Voltage gain About 150 About 500 Less than 1 2 Input resistance Low(about 75Ω) Low(about 750Ω) Very

high(about

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750KΩ) 3 Output

resistance Very high(about 450KΩ)

high(about 45KΩ) Low about 45Ω

4 Applications For high frequency applications

For audio frequency applications

For impedance matching

25. What are the biasing conditions to operate transistor in active region? Emitter-base junction has to be forward biased and collector-base junction to be reverse biased.

(16 MARKS) 1. Draw the circuit diagram of an NPN junction transistor CE configuration and

describe the static input and output characteristics.(16) i)circuit diagram (3) ii)Explanation of input and output characteristics curve (10) iii) advantages and disadvantages (3)

2. With necessary circuit and waveform. Explain the switching characteristics of a

transistor in detail.(16) i)Draw the circuit and waveform(6) ii)explanation about the switching characteristics (10)

3. Derive the expressions of input impedance ,output impedance , voltage and current gain in CE configuration using hybrid model.(16)

i) Input impedance(4) ii )output impedance(4) iii) voltage gain and current gain(6) iv) advantages and disadvantages (2)

4.(a) Explain in detail about power transistor and its characteristics.(12) i)Draw the symbol and characteristic curve(4) ii) explanation about the construction and working principle(8) (b) Write short notes on opto couplers.(4) 5.(a)Explain the construction of NPN and PNP transistor(6)

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(b) Explain CB transistor configuration with input and output characteristics.(10) i) Draw the input & output characteristics of CB configuration(5) ii) explain the working principle(5) 6. Using the hybrid equivalent model, analyses and deduce the expression for the parameters using the circuit sketch. What is the significance of this approach? (16)

i) Draw the hybrid equivalent model(4) ii) Deduction of parameters(12)

UNIT–III FET AND ITS APPLICATIONS (2 Mark Question & Answers)

1.Why the input impedance of FET is more than that of BJT FET will be reverse biased at input (GS) side hence the input impedance will be high where as the for the BJT input(EB) will be forward biased. 2. How a FET is used as Voltage Variable Resistor? By controlling the gate to source voltage the drain current will be controlled in the ohmic region. Hence a FET can be used as a Voltage Variable Resistor. 3. Why FET is called voltage controlled devices?

FET is called voltage controlled devices i.e, the output current (Id) is controlled by input voltage VGS.

4. Define Pinch off voltage in FET . Pinch off voltage is minimum drain to source voltage where the drain current approach constant value (saturation value) Beyond the Pinch off voltage the channel width can not be reduced. 5. What are the advantages of MOSFET over FET. 1. Very high input impedance 2. Small size and well suited for integrated circuit.

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6. What is instrinsic stand off ratio of a UJT . The ratio of V 1 (voltage between emitter and base 1) to V BB is called instrinsic stand off ratio η = RB1 / RB1+RB2 The value of η lies between 0.51 and 0.82 7. Mention a few applications of FET. As a low noise amplifier. As a buffer amplifier. In phase shift oscillator. 8. What is Inversion layer. In the construction of E-MOSFET, there are two layers of conductor which is sandwiched by SiO2 layer, which acts as a capacitor. When the gate is positive, it induces negative charge in the substitute which will form a part of drain current. This is called Inversion layer. 9. Write down the applications of MOSFET. i) As input amplifiers in oscilloscope, electronic voltmeters. ii) In computer memories. iii) In logic circuits. iv) In phase shift oscillators. v) In FM and TV receivers. 10. What is Holding current & Latching current? Holding current : It is that value of current below which the SCR switches from the conducting state to the forward blocking state Latching current : This is the minimum current flowing from anode to cathode when SCR goes from OFF to ON state and remain in ON state even after gate bias is removed. 11. Mention a few applications of SCR.

Relay control, phase control, static switches, regulated power supplies, heater controls, inverters, converters and motor control supply.

12. Name the factors which make the JFET superior to BJT? and also list the JFET parameters. High input impedance, low output impedance and low noise level. JFET parameters: Tran conductance (gm),drain resistance (rd) and amplification factor(µ) µ =gm.rd

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13. Mention the methods used for biasing circuits in FET. i) Self bias ii) Potential divider bias. 14. Explain the depletion mode of operation in MOSFET. When the gate is negative bias, the thickness of the depletion layer further increases of the induced positive charge. Thus the drain current decreases, as the gate is made more negative. This is called depletion of mode of operation. 15. Compare SCR with TRIAC. S.no SCR TRIAC

1 unidirectional current bidirectional current 2 triggered by positive pulse

at gate

triggered by pulse of positive or negative at gate

3 fast turn off time Longer turn off time 4 large current ratings lower current ratings

16. Differentiate BJT and UJT. S.no BJT UJT

1 It has two PN junctions It has only one PN junctions 2 three terminals present are emitter,

base,collector

three terminals present are emitter base1,base2

3 basically a amplifying device basically a switching device

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17.Write advantages of JFET. i) Input impedance of JFET is very high. This allows high degree of isolation between the input and output circuit. ii) Current carriers are not crossing the junction hence noise is reduced drastically. 18. Comparision of N-channel with P-channel FETS. i)In an N-channel JFET the current carriers are electrons, where the current carriers are holes in a P-channel JFET. ii)Mobility of electrons is large in N-Channel JFET ,mobility of holes is poor is P- channel JFET. 19. What are the applications of JFET transistor? - High Input Impedance Amplifier - Low-Noise Amplifier - Differential Amplifier - Constant Current Source - Analogue Switch or Gate - Voltage Controlled Resistor 20. What are the types of FET?

21. list the difference between JFET and BJT 1 Control

element Current controlled device. Input current Ib controls output current Ic

Voltage controlled device.Input Voltage VGS controls drain current Io

2 Device type Current flows due to both, majority and minority carriers and hence bipolar device

Current flows due to both, majority carriers and hence unipolar device

3 Types npn and pnp n-channel and p-channel

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4 Symbols

5 Configurations CB,CC,CE CD,CG,CS 6 Input

resistance Less compare to JFET High compare to BJT

7 Size Bigger than JFET Smaller in construction than BJT, thus making them useful in integrated circuits

8 Sensitivity Higher sensitivity to changes in the applied signals

Less sensitivity to changes in the applied voltage

9 Thermal stability

less more

22. Define amplification factor.

23.Why MOSFETs are never connected or disconnected in the circuit when power is ON? If a MOSFETs is connected or disconnected in the circuit when power is ON, the transient voltages caused by inductive kickback and other effects may exceed Vgs(max) and thus wipe out the MOSFET. 24. What is MOSFET? What are the types of MOSFET? MOSFET: Metal oxide semiconductor field effect transistor It is a second category of field effect transistor. Types: * Depletion MOSFET (D-MOSFET) * Enhancement MOSFET (E-MQSFET)

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25. Define pinch-off voltage and give expression? The ohmic relationship between VDS (drain to source voltage) and ID (Drain current) continues till VDS reaches a certain critical value called pinch-off voltage (Vp) when ID becomes constant at its maximum value called IDSS where e = 1.6 x10-19 c ε = dielectric constant of channel material; ND = no. of donor atoms (electrons/cm3)

16MARKS

1)a) Compare JFET and MOSFET.(any five) (5) b) Give a detailed description of construction and operation of JFET (11) i) Construction of P channel JFET and N-channel JFET(4) ii) explanation of JFET with VGG and VDD applied (5) iii) Show the voltage drop across the channel due to VDD(2) 2) a)Explain the operation of UJT hence draw its VI characteristics b) Draw the equivalent circuit of UJT and define the intrinsic stand off ratio. 3) Explain the operation of enhancement mode MOSFET with neat diagram and compare it with JFET.(16) i) Structure and physical operation (6) ii) Volt-amphere characteristics curve (5) iii) Explain the ohmic region, saturation region (3) iv) Advantages and disadvantages (2) 4) Explain the construction, working and operating characteristics of N-channel JFET’s with relevant diagrams. Give the applications of JFET’s. i) Structure and physical operation (6) ii) brief explanation of operation (4) iii)drain characteristics and transfer characteristics(4) iv) advantages and disadvantages (2) 5) Write the construction, operation and characteristics behavior of JFET under various

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biasing conditions. Give necessary figures (16) i)Construction ii) Characteristics curve iii)Biasing conditions

6) (i) Draw and explain the small signal low frequency model of JFET? (16)

UNIT – IV

AMPLIFIERS AND OSCILLATORS (2 Mark Question & Answers)

1. Why CE amplifier is most widely used?

The common emitter amplifier is used in 95% of the applications because of the following reasons:

a. High current gain. b. High voltage gain and power gain. c. Moderate output to input impedance ratio.

2. What are the advantages of RC coupling?

i) It requires cheap components like resistors and capacitors. ii) It gives uniform voltage amplification over a wide frequency range . iii) No transformer is used so minimum nonlinear distortion and no electromagnetic interference.

iv) Overall amplification is higher. 3. What are the disadvantages of RC coupling? a) Due to large voltage drop across collector load resistors, the collectors work at

relatively small voltages unless higher supply voltage is used to overcome this voltage drop.

b) It is noisy in humid weather.

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c) The impedance matching is poor as the output impedance of the RC coupled amplifier is several hundred ohms while that of a speaker is only a few ohms. hence amount of power transferred to the speaker is reduced.

4. What are the differences in performance of an RC coupled amplifier over the

single stage? a) Its overall amplification is higher. b) Its nonlinear distortion is less. c) It has better fidelity over a wide frequency range. d) Its frequency response is much better over the audio frequency range.

5. What are the types of amplifier based on frequency response? a) Audio frequency amplifiers(20 Hz to 20KHz) b) Radio frequency amplifiers(a few KHz to 100 MHz) c) Ultra-high frequency amplifiers(100 or 1000 MHz)

6. State the various methods of cascading transistor amplifiers.

• Direct coupling

• Resistance capacitance coupling

• Transformer coupling.

7. What do you mean by a multistage amplifier? The voltage gain obtained from a single stage small signal amplifier is limited.

Moreover it is not sufficient for all practical applications. In order to achieve greater voltage and power gain we have to use more than one stage of amplification. Such an amplifier is called a multistage amplifier.

8. What are the distortions in amplifiers?

a) Non linear distortion. b) Frequency distortion. c) Delay distortion.

9. State Barkhausen criterion of oscillation. The essential conditions for maintaining oscillations are:

• ,1=βA i.e. the magnitude of loop gain must be unity.

The total phase shift around the closed loop is zero or 360 degrees

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10. What do you understand by feedback in amplifiers?

A part of output is sampled and fed back to the input of the amplifier is called

feedback.

11. Define negative and positive feedback. If the feedback signal (voltage or current) is applied in such a way that it is in phase

with the input signal and thus increases it, then it is called a positive feedback. It is also known as regenerative feedback or direct feedback. If the feedback signal (voltage or current) is applied in such a way that it is out of phase with the input signal and thus decreases it, then it is called a negative feedback. It is also known as degenerative feedback or inverse feedback.

12. List out four different ways of connecting the feedback amplifier.

• Voltage –series feedback. • Voltage –shunt feedback. • Current –series feedback. • Current - shunt feedback.

13. Give the expression for gain of an amplifier without feedback and with

negative feedback.

i

o

vV

VA = (Gain without feedback)

s

o

vfV

VA = (Gain with feedback)

14. What are the advantages of using negative feedback amplifiers?

• Increased stability. • Less frequency and phase distortion • Increased bandwidth • Increases input impedance and decreases output impedance.

15. What is an oscillator?

An oscillator is an amplifier which uses a positive feedback and without any external input signal, generates an output waveform at a desired frequency.

16. What are the factors which affect the frequency stability of an oscillator? • Due to change in temperature, the values of the frequency – determining

components, viz., resistor, inductor and capacitor, will change. • Due to variation in the power supply, unstable transistor parameters,

change in climatic conditions and aging.

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• The effective resistance of the tank circuit is changed when the load is connected.

• Due to variation in biasing conditions and loading conditions. 17. What type of oscillations produced if phase shift around a loop is 360o and

βA >1.

When the total phase shift around a loop is 0o or 360o and βA >1, then the

output oscillates but the oscillations are of growing type. The amplitude of oscillations goes on increasing.

20. State the frequency of oscillations for the RC phase shift oscillator.

RCf

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1

π=

18. Compare RC phase shift and wien bridge oscillator. S.No RC Phase Shift Oscillator Wien Bridge oscillator 1. The feedback network is RC

network with three RC sections The feedback network is lead- lag network which is called Wien bridge circuit

2. The amplifier introduces 180o phase shift and the feedback network introduces 180o phase shift.

The amplifier and the feedback circuit does not introduce any phase shift.

3. The frequency variation is difficult

By mounting the two capacitors on common shaft and varying the values, frequency can be varied.

4. Amplifier gain condition is A ≥29

Amplifier gain condition is A ≥3

19. What is the advantageous feature of a crystal oscillator? The advantage of the crystal is its very high Q as a resonant circuit, which results in good frequency stability for the oscillator.

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20. Enumerate the effects of negative feedback on the various characteristics of the amplifier.

Type of Feedback Characteristic Current -series

Voltage-series

Voltage-shunt

Current-shunt

Voltage gain Decreases Decreases Decreases Decreases Bandwidth Increases Increases Increases Increases Harmonic distortion

Decreases Decreases Decreases Decreases

Noise Decreases Decreases Decreases Decreases Input resistance

Increases Increases Decreases Decreases

Output resistance

Increases Decreases Decreases Increases

21. In a Wien - bridge oscillator, if the value of R is 100KΩ, and frequency of oscillation is 10 KHz, find the value of capacitor C. The operating frequency of a Wien- bridge oscillator is given by

RC

fr

π2

1=

rRf

Cπ2

1=∴ = 159pF.

22. What are the types of feedback oscillators?

* RC- Oscillator RC Phase shift oscillator Wien bridge oscillator. * LC-Oscillators

Hartley Oscillator Colpitts Oscillator Clapp Oscillator 23.Define CMMR. The common mode rejection ratio(CMMR) of a differential amplifier is defined as the ratio of the differential mode gain to common mode gain.

24. Define frequency stability in oscillator?

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The measure of ability of an oscillator to maintain the desired frequency as precisely as possible for as long a time as possible is called as frequency stability of an oscillator. 25.Write the disadvantages of phase shift oscillator and LC oscillator. Disadvantages of phase shift oscillator: i)It is necessary to change the C or R in all the three RC networks simultaneously for changing the frequency of oscillations.This is practically difficult. ii) it is not practical for high frequencies. Disadvantages of LC oscillator

i) The frequency stability is not very good.

ii) They are too bulky and expensive and cannot be used to generate low frequencies.

16 MARKS

1. Discuss the different voltage/ current – series /shunt feedback connections with

expression for gain , input resistance and output resistance of differential amplifier.

i) gain(5)

ii) input resistance(5)

iii)output resistance(6)

2. with a neat diagram explain the working principle of a wein bridge oscillator and derive

the expression for its frequency of oscillation.

i) circuit diagram (5)

ii) brief explanation about operation (5)

iii) condition should be proved(6)

3. Explain the working of Colpitt’s oscillator and derive an expression for frequency of

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oscillation for Colpitt’s oscillator.




4. With a neat sketch explain the working of an RC phase shift oscillator and derive an

expression for frequency of oscillation for an RC phase shift oscillator.




5.a) Explain in detail about the different feedback topologies.

b) Write notes on Wien bridge oscillator.

6. a) Differentiate oscillator with amplifier. (4)

b) Draw the circuit of a Hartley oscillator and derive the condition for the frequency of

oscillation. (12)

i) draw the circuit diagram (5)

ii)condition for the frequency(7)

30

UNIT – V PULSE CIRCUITS

(2 Mark Question & Answers)

1. What is meant by linear wave shaping? The process by which the shape of a non sinusoidal signal is changed by passing the

signal through the network consisting of linear elements is called linear wave shaping. 2. What are the types of non sinusoidal waveform?

• Step waveform • Pulse waveform • Square waveform • Ramp waveform

3. What is a ramp or sweep waveform?

A waveform which is zero for all t<0 and then increases linearly with time for t>0 is called a ramp or sweep waveform.

4. What is the function of capacitor in high pass RC circuit?

At very high frequency, the capacitor almost acts as a short circuit and all the input appears at the output. At zero frequency i.e. for D.C. input, the reactance becomes infinite and hence offers open ciruit.Thus the capacitor totally blocks D.C., not allowing it to reach output. Hence the capacitor is called blocking capacitor.

5. When the capacitor is called a blocking capacitor in a high pass RC circuit?

At zero frequency i.e. for D.C. input, the reactance becomes infinite and hence offers open ciruit.Thus the capacitor totally blocks D.C., not allowing it to reach output. Hence the capacitor is called blocking capacitor.

6. What is a clipper or limiter or slicer? The circuits which are used to clip off unwanted portion of the waveform, without

distorting the remaining part of the waveform are called clippers

7. What are a serial clipper and parallel clipper? Serial clipper: The serial clipper is a circuit in which diode is connected in series with the load.

Parallel clipper: The parallel clipper is a circuit in which diode is connected parallel to the load.

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8. What are a negative clipper circuit and positive clipper circuit? Negative clipper circuit:

Negative clipper is one which clips off negative half cycle of the input. Positive clipper circuit: Positive clipper is one which clips off positive half cycle of the input.

9. What is a negative clamper? A negative clamper which adds a negative level to the a.c. output.

10. What is a multivibrator? The electronic circuits which are used to generate nonsinusoidal waveforms are

called multivibrators. 11. What is a bistable multivibrator? A bistable multivibrator is a circuit with both stable states. it has no unstable states.

12. What is a monostable multivibrator? The monostable multivibrator is a circuit which has only one stable state and other

state is an unstable referred as quasi stable state.

13. What is astable multivbrator? The astable multivibrator has both the states as quasi stable states. None of the

states is stable state.

14. What are the applications of bistable multivibrator? • Used for the performance of many digital operations like counting and

storing of digital information. • Used as a memory element in shift registers, counters etc. • Used in processing pulse type waveforms. • Used to generate the symmetrical square wave. • Used as a frequency divider.

15. What are applications of monostable multivibrator?

• Used to produce rectangular waveform and hence used as a gating circuit.

• Used to introduce time delays as gate width is adjustable. • Used to generate uniform width pulses from a variable width input pulse

train.

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16. What are the applications of astable multivibrator? • Used as a square wave generator, voltage to frequency converter etc. • Used as a clock for binary logic signals. • Used in digital voltmeter and switched mode power supplies. • Used as an oscillator to generate wide range of audio and radio

frequencies. 17. What is an unsymmetrical triggering? In unsymmetrical triggering, two trigger inputs are used, one to set the circuit in

one particular stable state and other to reset the circuit to the opposite state.

18. What is a symmetrical triggering? The symmetrical triggering uses only one trigger input to the input of any one

transistor.

19. What is a Schmitt trigger? It is a wave shaping circuit which is used to generate square wave from a sine wave

input.

20. What are the applications of Schmitt trigger? • Amplitude comparator. • Squaring circuit.

21. What is an UJT relaxation oscillator?

The pulse signal required to drive the digital circuits can be obtained from a single stage oscillator circuits using a particular device like UJT.such an oscillator which uses UJT is called UJT relaxation oscillator.

22. What is a stable state of a bistable multivibrator? The stable state of bistable multivibrator is one in which the currents and voltages

satisfy Kirchhoff’s laws and are consistent with the device characteristics and it satisfies the condition that its loop gain is less than unity.

23. What is called as clipper circuits? The circuits which are used to clip off unwanted portion of the waveform, without disturbing the remaining part of the waveform are called clipper circuits or clippers. 24. What is the difference between the output from a clipper and a clamper?

The output of the clipper appears as if portions of the input signal were clipped off, but clamper simply shifts the input to a different DC level.

33

25.Define high pass filter. At very high frequencies the capacitior acts as a virtual short circuit and the output falls to zero.Hence this circuit passes the low frequencies of the input and attenuates the high frequency is called low pass filter.

16 MARKS

1. (a) Describe the operation of UJT and its emitter characteristics. (8) i)Brief explanation about UJT operation

b) Describe the working of a Schmitt trigger circuit with the help of necessary waveforms. (8) 2. (a) Sketch the response of RC high pass filter for the following inputs and explain. (1) Ramp (2) Pulse. (8) b) Explain the operation of a bistable multi-vibrator circuit with neat sketch. (8) (i)circuit diagram (3) ii)brief explanation of operation(5) 3. a)With the help of circuit diagram, describe the operation of a clipper that can clip at two independent levels.

i) circuit diagram (4) ii) brief explanation about two level clipping(4)

b) With a neat sketch, explain the working of an astable multivibrator. 4. What do you understand by clamping circuits? Discuss with the help of waveforms, the operation of a clamping circuit to clamp a sine wave input positively at 0 V.

i)circuit diagram (4) ii)brief explanation about sine wave input(12)

5.i). Explain the working of UJT based saw tooth oscillators. ii) With a neat sketch, explain the working of an Monostable multivibrator.

i) circuit diagram (4) ii) brief explanation about working principle(4)

6.What do you understand by clamping circuits? Discuss with the help of waveforms, the operation of a clamping circuit to clamp a sine wave input positively at 0 V.(16)

34

UNIVERSITY QUESTIONS WITH ANSWERS(Q.P-1)

B.E./B.Tech. DEGREE EXAMINATION, NOVEMBER/DECEMBER 2009 Third Semester

Electrical and Electronics Engineering EE 2203 — ELECTRONIC DEVICES AND CIRCUITS

(Regulation 2008) Time : Three hours Maximum : 100 Marks

Answer ALL Questions PART A — (10 × 2 = 20 Marks)

1. What is diffusion current in PN Junction diode? A concentration gradient exists, if the number of either electrons or holes is greater in one region of a semiconductor as compared to the rest of the region. The holes and electron tend to move from region of higher concentration to the region of lower concentration. This process in called diffusion and the current produced due this movement is diffusion current.

2. What is LED? Which material is used for LED? The PN junction diode can emit light through a process known as electroluminescence . When a diode is forward biased, majority of the carriers or both side of the junction will cross the junction potential barrier .This recombination emission is responsible for the diode emitting light. The following materials are used as i) Gallium Arsenic Zinc Antimony ii) Gallium Phosphorous iii) GA AS Ps iv) Ga PN

3. Why Base is lightly doped & width of the Collector large?


4. What do you understand by Q-point? For proper operation of a transistor in any application, we set a fixed level of certain currents and voltages in a transistor. These values of currents and voltages define the point at which the transistor operates. This point is called operating point. It is also known as quiescent point or Q-point. Since the level of currents and voltages are fixed, therefore the operating point is also called d.c operating point.

35

5.What are the special features of FET? Construction of the conducting channel is accomplished using the field effect a voltage between the gate and source is applied to reverse bias the gate-source pn-junction, thereby widening the depletion layer of this junction (see top figure), encroaching upon the conducting channel and restricting its cross-sectional area. The depletion layer is so-called because it is depleted of mobile carriers and so is electrically non-conducting for practical purposes 6. Define : (a) Pinch off voltage

Pinch off voltage is minimum drain to source voltage where the drain current approach constant value (saturation value) Beyond the Pinch off voltage the channel width can not be reduced.

(b) Amplification factor in JFET.

7. What is meant by Common mode Rejection Ratio? The common mode rejection ratio(CMMR) of a differential amplifier is defined as the ratio of the differential mode gain to common mode gain.

8. Give the Barkhausen’s criterion for oscillators. The essential conditions for maintaining oscillations are:

• ,1=βA i.e. the magnitude of loop gain must be unity.

.The total phase shift around the closed loop is zero or 360 degrees 9. Mention some applications of UJT. i). It is used in timing circuits ii). It is used in switching circuits iii) It is used in phase control circuits iv). It can be used as trigger device for SCR and triac. v) It is used in saw tooth generator. vi) It is used for pulse generation.

36

10. What is a multivibrator? The astable multivibrator has both the states as quasi stable states. None of the states is stable state. The types are i)bistable multivibrator ii)Monostable multivibrator iii)astable multivibrator

PART B — (5 × 16 = 80 Marks) 11. (a) (i) Draw and Explain the VI characteristics of a PN Junction diode. (6)

* Draw the V-I characteristics curve (2) * Brief explanation about operation held in forward and reverse bias (4)

(ii) Explain the operation of a Full wave Rectifier and derive its Ripple factor. (10)

• Circuit digram(2) • Working principle of operation(4) • Ripple factor(4)

Or (b) (i) Explain the working of a Zener diode as a Regulator. (8) *Diodesymbol & circuit diagram(4) * explain the reverse bias operation(4) (ii) Discuss the working principle, characteristics and applications of LED in detail. (8)

*symbol and its explanation(2) *working principle (6) * Application of LEDs fall into three major categories (8)

12. (a) (i) Draw and explain the Input and Output characteristics of a BJT in CE configuration. (12)

*circuit diagram (3) *Explanation of input and output characteristics curve 6) * advantages and disadvantages (3)

(ii) Write a note on optocouplers. (4) Or

37

(b) (i) Draw the Hybrid model of CE configuration and also derive the expressions for its Input and Output Impedances, current and voltage gain. (12)

*Draw the hybrid equivalent model(4) *Deduction of parameters(8)

(ii) Explain the switching characteristics of a transistor. (4) 13. (a) Explain in detail the construction and working principle of Depletion MOSFET. Also explain how Depletion MOSFET acts both in enhancement and depletion mode.(16) * circuit diagram for construction(5) * characteristics curve for both types(6) * MOSFET explanation(5) Or (b)(i) With a neat circuit diagram explain the operation of a common source amplifier. (6) *circuit diagram (2) *explain characteristics curve & current flow direction(4) (ii) From the low frequency model, determine the input and output impedances and the voltage gain of a JFET. (10) 14. (a) (i) Discuss the various topologies of feed back amplifier. (8) *shunt-series(2) *series-shunt(2) *shunt-shunt(2) *series-series(2) (ii) Discuss the operation of a colpitts oscillator in detail. (8) *circuit diagram (2)

* brief explanation about operation (3)

* condition should be proved(3)

Or (b) (i) Explain the effects of negative feedback in amplifiers. (8) (ii) Describe the operation of a typical voltage shunt feedback amplifier.(8) *circuit diagram(4) *operation(4)

38

15. (a) (i) What is a clipper and clamper? Explain the concept of a positive clipper and a clamper. (12) *definition for clipper & clamper(4) *differentiate positive & negative clipper(8) (ii) Distinguish between Astable and Bistable multivibrators. Mention some applications. (4) * compare the number of stable states *Applications Or (b) (i) What is a Schmitt Trigger? Discuss any two applications of Schmitt Trigger. (8) *Definition(2) *applications(6) (ii) Explain the application of UJT as a Sawtooth oscillator. (8) *draw the symbol & circuit diagram (2) *UJT operation(3) * explain with example(3) ANNA UNIVERSITY OF TECHNOLOGY OF TECHNOLOGY , COIMBATORE(Q.P-2)

B.E/B.TECH. DEGREE EXAMINATIONS ;NOV/DEC2011 REGULATIONS:2008 THIRD SENESTER :EEE

080280018- ELECTRONIC DEVICES AND CIRCUITS Time :3 hours Max.marks:100

Part –A (10*2=20 marks)

1. Name some donar and acceptor impurities

donars : Boron, Indium, Gallium, Aluminium. acceptors : Phosporous, Arsenic, Antimony .

2. Name the materials are used to construct an LED

i) Gallium Arsenic Zinc Antimony

ii) Gallium Phosphorous

iii) GA As Ps

iv) Ga PN

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3. When a transistor is used as a switch . in which regions of output characteristics it is operated.

The transistor acts as a switch when it is operated at either cutoff region or saturation region.The output characteristics operated at active region

4. In a bipolar transistor ,which region is wider and which is thinner.


5. Mention the applications MOSFET?

• As input amplifiers in oscilloscope, electronic voltmeters. • In computer memories. • In logic circuits. • In phase shift oscillators. • In FM and TV receivers.

6. Sketch the ohmic region in a drain characteristics of JFET

7. List the advantages of negative feedback?

• Increased stability.

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• Less frequency and phase distortion • Increased bandwidth • Increases input impedance and decreases output impedance.

8. Name the various types of oscillator .

* RC- Oscillator RC Phase shift oscillator Wien bridge oscillator. * LC-Oscillators Hartley Oscillator Colpitts Oscillator Clapp Oscillator

9. What are clipper and clamper

Clipper: • Negative clipper is one which clips off negative half cycle of the input. • Positive clipper is one which clips off positive half cycle of the input.

Clamper: The circuits which are used to add D.C. level as per the requirements to the a.c.

output signal are called clamper circuits.

10. Give any two application of multi vibrators.

a. Used for the performance of many digital operations like counting and storing of digital information.

b. Used to generate uniform width pulses from a variable width input pulse train.

c. Used as an oscillator to generate wide range of audio and radio frequencies.

PART B (5*16=80 marks)

11. (a) With neat circuit diagram explain the operation of a full – wave rectifier with

41

necessary waveforms ? also mention its application.(16)

• Circuit diagram(2) • Oeration on both positive and negative half cycle(10) • Applications(4)

Or

(b) what is voltage regulator ? explain the working principle of any series regulator type with circuit diagram .(16)

• Definition(2) • Types(2) • Brief explanation of oeration(8) • Circuit diagram(4)

12. (a) with necessary circuit and waveform. Explain the switching characteristics of a

transistor in detail. (16) • Circuit diagram(5) • Switching characteristics curve(5) • Brief explanation about working principle(6)

Or

(b) Draw and explain the input and output characteristics of CE configuration. Justify with CE Configuration is preferred over other transistor configuration.(16)

• Working principle(4) • Characteristics curve(4) • Comparison of CB,CE,CC(8)

13. (a) Explain the performance of FET as a voltage variable resistor also mention its advantages and applications.(16)

• Construction(4)

• Operation (6)

• Advantages(3)

• Applications(3)

Or

(b) Explain the construction, working principle and characteristics of p- channel enhancement MOSFET.(16)

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• Construction(4)

• Working principle of operation(4)

• Characteristic curve explanation(8)

14.(a) Discuss the different voltage/ current – series /shunt feeback connections With expression for gain , input resistance and output resistance of differential amplifier. (16)

• Definition for feedback(2) • Types(2) • Series-shunt connections(4) • Input & output resistance(8)

Or (b) with a neat diagram explain the working principle of a wein bridge oscillator and derive the expression for its frequency of oscillation .(16)

• Circuit diagram(4) • Working principle(4) • Frequency of oscillation(8)

15.(a) explain the operation of Schmitt trigger .also define the following in a Schmitt trigger operation I) upper trigger point II)lower trigger point III) hysteresis and regeneration(16) Or (b). Draw the circuit diagram of an astable multi vibrator .(16)

• Circuit diagram(4) • Waveforms(4) • Operation (8)

43

B.E./B.Tech. DEGREE EXAMINATION, APRIL/MAY 2010

Third Semester Electrical and Electronics Engineering

EE2203 — ELECTRONIC DEVICES AND CIRCUITS(Q.P-3) (Regulation 2008)

Time: Three hours Maximum: 100 Marks Answer ALL Questions

PART A — (10 × 2 = 20 Marks) 1. What is meant by diffusion current in a semi conductor? There may exist an additional current due to the transport of charge in a Semi conductor. Such an additional current is due o the phenomenon called diffusion. The current due to the diffusion is called diffusion current. 2. A silicon diode has a saturation current of 7.5 µA at room temperature 300°K. Calculate the saturation current at 400°K. Formula:

I300=10µA T1=300K T2=400K

I400=I300*7.5-6*210 =150mA

Ans: 150mA 3. Draw the input and output characteristics of a transistor in CE configuration and mark the cutoff, saturation and active regions.

Input characteristics

Output characteristics

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4. State the advantages of optocoupler. (Write any four).

• Economical • Solid state reiiability • Medium to high speed signal transmission • DC & low frequency transmission • High voltage isolation • High isolation impedance • Small size DIP Package • No contact bounce • Low power operation

5. Compare JFET with BJT.

S.no BJT JFET 1 Current controlled device voltage controlled device 2 Input resistance is less compared to JFET High compared to BJT 3 Size is better than JFET smaller than BJT 4 Current flows to both majority and minority

carriers and hence bipolar device Current flows only due to majority carriers and hence uniipolar device

45

6. Define amplification factor in JFET.

7. Define CMRR and write its significance in differential amplifiers. The common mode rejection ratio(CMMR) of a differential amplifier is defined as the ratio of the differential mode gain to common mode gain.

Significance:High CMRR produce more accuracy 8. List the advantages of negative feedback amplifiers.

• Increased stability. • Less frequency and phase distortion • Increased bandwidth • Increases input impedance and decreases output impedance.

9. Sketch the idealized characteristics for the filter types. (a) Low pass (b) High pass (c) Band pass (d) Band reject filters. 10. Define intrinsic stand off ratio of UJT and draw its equivalent circuit. The ratio of V 1 (voltage between emitter and base 1) to V BB is called instrinsic stand off ratio η = RB1 / RB1+RB2 The value of η lies between 0.51 and 0.82

46

PART B — (5 × 16 = 80 Marks)

11. (a) With a neat diagram explain the working of a PN junction diode in forward bias and reverse bias and show the effect of temperature on its V-I characteristics. (16)

• Circuit diagram &symbol(4) • Diode operation in first & third quadrant(6) • Dtaw the V-I characteristics curve(2) • Temperature effecton diode(4)

Or (b) (i) Explain V-I characteristics of Zener diode. (8)

o Draw the V-I characteristic curve(2) o Operation on first & third quadrant(6)

(ii) Draw the circuit diagram and explain the working of full wave bridge rectifier and derive the expression for average output current and rectification efficiency. (8)

• Circuit diagram(2) • Working principle(3) • Expression for output current & efficiency(3)

12. (a) (i) Draw the h-parameter equivalent circuit of a transistor in CE configuration. (8)

• Draw equivalent circuit (4) • Derive the h-parameters(4)

(ii) Describe the methods of determination of h-parameters from its static Input and output characteristics. (8)

• H-parametrs derive(4)

47

• Draw the characteristic curve parameters(4) Or

(b) (i) Explain the important characteristics of optocoupler. (6) (ii) Explain the switching characteristics of transistor with neat sketch.(10)

• Switching characteristic curve(4) • Explanation(6)

13. (a) (i) Explain how the transconductance of a JFET varies with drain current and gate voltage characteristics and transfer characteristics. (12)

• Draw drain and transfer characteristics curve(4) • Explanation(8)

(ii) A JFET has the following parameters IDDS = 32 mA, VGS(off) = -8 Volts, VGS = -4.5 Volts. Find the values of drain current. (4) Or (b) (i) Explain the working of n-channel enhancement type MOSFET.Sketch its typical characteristics. (10)

• Construction(4) • Characteristics curve(4) • Advantages(2)

(ii) Explain the application of FET as a voltage variable resistor. (6) 14. (a) (i) Draw the block diagram of a voltage series feedback amplifier and derive the equation for input impedance, output impedance and the voltage gain. (10)

• Block diagram(4) • Input impedance(2) • Output impedance(2) • Voltage gain(2)

(ii) Calculate the voltage gain, input and output resistances of a voltage series feedback amplifier having AV = 300, Ri = 1.5 k, Ro = 50 k and β = 1/15. (6) Or (b) (i) Differentiate oscillator with amplifier. (4) (ii) Draw the circuit of a Hartley oscillator and derive the condition for the frequency of oscillation. (12)

• Circuit diagram(4) • Working principle(4) • Condition for frequency of oscillation(4)

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15. (a) (i) Describe the operation of UJT and its emitter characteristics. (8)

• Circuit diagram & symbol(2) • Characteristics curve(6)

(ii) Describe the working of a Schmitt trigger circuit with the help of necessary waveforms. (8)

• Circuit diagram & waveforms(4) • Working principle(4)

Or (b) (i) Sketch the response of RC high pass filter for the following inputs and explain. (1) Ramp (2) Pulse. (8) (ii) Explain the operation of a bistable multi-vibrator circuit with neat sketch. (8)

• Circuit diagram (3) • Working principle & brief explanation(5)

ee2203-electronic devices and...

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