EDC- 2 MARKS WITH ANSWER1.pdf

8/14/2019 EDC- 2 MARKS WITH ANSWER1.pdf

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EE2203-ELECTRONIC DEVICES AND CIRCUITS 2 MARKS

M.S/ EEE-V.V.C.E.T Page 1

1. What is an ideal diode?An ideal diode is one which offers zero resistance when forward biased and infinite

resistance when reverse biased.

2. Compare ideal diode as a switch.An ideal diode when forward biased is equivalent a closed (ON) switch and whenreverse biased, it is equivalent to an open (OFF) switch.

3. State the mathematical equation which relates voltage applied across thePN junction diode and current flowing through it.

4. Define knee/cut-in/threshold voltage of a PN diode.It is the forward voltage applied across the PN diode below which practically nocurrent flows.

5. What is the effect of junction temperature on cut-in voltage of a PNdiode?Cut-in voltage of a PN diode decreases as junction temperature increases.

6. What is the effect of junction temperature on forward current and reverse

current of a PN diode?For the same forward voltage, the forward current of a PN diode increases andreverse saturation current increases with increase in junction temperature.

7. Differentiate between breakdown voltage and PIV of a PN diode.

The breakdown voltage of a PN diode is the reverse voltage applied to it at which thePN junction breaks down with sudden rise in reverse current. Whereas, the peakinverse voltage (PIV) is the maximum reverse voltage that can be applied to the PNjunction without damage to the junction.

8. Differentiate avalanche and zener breakdowns.Avalanche Breakdown

1. Breakdown occurs due to heavily doped junction and applied strong electricfield.

2. Doping level is high.3. Breakdown occurs at lower voltage compared to avalanche breakdown

Zener Breakdown1. Breakdown occurs due to avalanche multiplication between thermally generatedions.2. Doping level is low.3. Breakdown occurs at higher voltage.


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9. Draw the V-I characteristics of an ideal diode.

10. Differentiate between drift and diffusion currents.

Drift Current1. It is developed due to potential gradient.2. This phenomenon is found both in metals and semiconductors

Diffusion Current1. It is developed to charge concentration gradient.2. It is found only in semiconductors.

11. Draw the V-I characteristics of a practical PN diode.

12. List the PN diode parameters.1. Bulk Resistance.2. Static Resistance/Junction Resistance (or) DC Forward Resistance3. Dynamic Resistance (or) AC Forward Resistance4. Reverse Resistance5. Knee Voltage6. Breakdown Voltage7. Reverse Current (or) Leakage Current

13. State the PN diode ratings.Even PN-Junction has limiting values of maximum forward current, peak inversevoltage and maximum power rating.


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14. Define reverse recovery time.It is maximum time taken by the device to switch from ON to OFF stage.15. List the PN diode switching times.1. Recovery Time2. Forward Recovery Time3. Reverse Recovery Time4. Reverse recovery time,5. Storage and Transition Times

16. Define transition capacitance of a diode.Transition Capacitance (CT) or Space-charge Capacitance: When a PN-junction isreverse-biased, the depletion region acts like an insulator or as a dielectric.The P- and N-regions on either side have low resistance and act as the plates. Henceit is similar to a parallel-plate capacitor. This junction capacitance is called transitionor space-charge capacitance (CT).It is given by

Where, A = Cross-sectional area of depletion region.D = Width (or) thickness of depletion region.Its typical value is 40 pF.Since the thickness of depletion layer depends on the amount of reverse bias, CT canbe controlled with the help of applied bias.This property of variable capacitance is used in varicap or varactor diode.

This capacitance is is voltage dependent and is given by

Where, VK= Knee voltage,VR= Applied reverse voltage,K = Constant depending on semiconductor material,n =1/2 for alloy junction,

= 1/3 for diffused junction.

17. Define diffusion capacitance of a diode.

Diffusion or Storage Capacitance (CD): This capacitive effect is present when thejunction is forward-biased.It is called diffusion capacitance due to the time delay in minority charges across thejunction by diffusion process. Due to this fact, this capacitance cannot be identified interms of a dielectric and plates. It varies directly with forward current. When aforward-biased PN-junction is suddenly reverse biased, a reverse current flows whichis large initially, but gradually decreases to the level of saturation current, I0.This effect can be likened to the discharging, of a capacitor and is, therefore calleddiffusion capacitance, CD. Its typical value is 0.02 FIt is given by:


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Where, = Mean life time of carrier

= Constant =2 for Si and 1 forGeI = Forward currentI0 = Reverse saturation currentVT= Volt equivalent of temperature

18. Draw the V-I characteristics of a zener diode.

19. List some applications of zener diode.Zener diode find wide commercial and industrial applications. Some of their common

applications are: As voltage regulators. As peak clippers or voltage limiters. For wave shaping. For meter protection against damage from accidental application of excessive

voltage.

As a fixed reference voltage in a network for biasing and comparison purposesand for calibrating voltmeters.

20. State the ratings of zener diode.

Zener voltage (Vz):The voltage at which a zener diode breaks in the reverse biascondition is called zener voltage. In fact, it is the voltage at which a zener diode is to


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operate. The value of zener voltage depends upon doping-more the doping, lesserthe breakdown voltage.

Tolerance: The range of voltages about the breakdown voltage in which a zenerdiode conducts in reverse direction is called tolerance.

Power Rating (PZM):The maximum power which a zener diode can dissipate (orhandle) without damage is called its power rating.

PZM = IZM x VZ

Maximum Current Rating (IZM): The maximum value of current which a zenerdiode can handle at its rated voltage without damage is called maximum currentrating (IZM).

Zener resistance (RZ):The opposition offered to the current flowing through thezener diode in the operating region is called zener resistance (RZ) or zenerimpedance (ZZ).

21. State the principle of operation of an LED.

When a free electron from the higher energy level gets recombined with the hole , itgives out the light output. Here, in case of LEDs, the supply of higher level electronsis provided by the battery connection.

22. State any four advantages of LED.

They are small in size. Light in weight. Mechanically rugged. Low operating temperature. Switch on time is very small. Available in different colours. They have longer life compared to lamps. Linearity is better. Compatible with ICs. Low cost.

23. State some disadvantages of LED.

Output power gets affected by the temperature radiation. Quantum efficiency is low. Gets damaged due to over voltage and over-current.

24. List the applications of LED.

They are used in various types of displays.

They are used as source in opto-couplers. Used in infrared remote controls. Used as indicator lamps. Used as indicators in measuring devices.


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29. Compare LEDs and LCDs.

LEDs LCDs1. More power is required.2. Fastest displays3.

More life.4. LED is light source.

5. More temperature range.6. Mounting is easy

1. Less power is required.2. Slowest displays.3.

Less life.4. LCD is not light source. It is alight reflector.

5. Less temperature range6. Mounting is difficult.

30. Define rectifier. Mention the types.

Rectifier: A rectifier is a circuit that converts AC into pulsing DC. It usesunidirectional conducting devices like PN diodes.Rectifiers are classified into two types based on the conduction of AC input.They are:

Half wave rectifier (HWR). Full wave rectifier (FWR).

Half Wave Rectifier (HWR):The HWR uses the property of diode that conductscurrent in one direction only. It uses only one diode as in Fig.1.12.During the positive half-cycles of the input AC voltage, the diode D is forward biased(ON) and conducts. While conducting, the diode acts as a short-circuit so that thecircuit current flows and hence the positive half cycles of input AC voltage aredropped across the load RL.

During the negative input half cycles, the diode D is reverse biased (OFF) and so,does not conduct, i.e., there is no current flow. Hence there is no voltage drop acrossRL. Thus, the negative half cycles are suppressed, i.e., they are not utilized fordelivering power to the load.

Hence, the HWR uses only positive half-cycles of the input AC supply. However theoutput is not steady DC, but only a pulsating DC with ripple frequency equal to thatof the input voltage frequency.i.e., fr = fin

Also, PIV = Vm, where Vm is the maximum secondary voltage.

Full Wave Rectifier (FWR):In a FWR, both the half-cycles of the input AC supplyare utilized. Alternate half-cycles are inverted to give a unidirectional load current.


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There are two types of FWRs. Centre-tapped FWR. Bridge rectifier.

31. Define rectifier efficiency.It is defined as the ratio of DC power output to the applied AC power in putRectifier efficiency.

32. Define ripple factor of a rectifier.The purpose of a rectifier is to convert AC into DC. But the pulsating output of arectifier contains a DC component and an AC component, called ripple.

The ratio of RMS value of AC components to the DC component in the rectifier outputis called ripple factor.The ripple factor is very important in deciding the effectiveness of a rectifier. Itindicates the purity of the DC power output. The smaller the ripple factor, the lesserthe effective AC component and hence more effective is the rectifier.

33. Define TUF of a rectifier.Most of the rectifier circuits make use of transformer whose secondary feeds the ACpower. The transformer rating is necessary to design a power supply.Transformer utilization factor (TF) id defined as the ratio of DC power delivered to

the load to the AC power rating of transformer secondary.

34. Give the advantages and disadvantages of HWR and FWR.Half Wave Rectifier (HWR)Advantages

Simple circuit. Low cost.

Disadvantages. Rectification efficiency is low (40.6%). Very high amount of ripple ( = 1.21) Low TUF (0.287) Saturation of transformer core occurs.


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35. What is the need for a filter in rectifier?The output of a rectifier is pulsating and contains a steady DC component withundesirable ripples. If such pulsating DC is given to the electronic circuits, itproduces disturbances and other interferences. Hence ripples have to be kept farfrom the load. This is achieved by use of a filter circuit in between the rectifier andload as shown below.

36. What is a rectifier-filter? List the different types of filters.A filter circuit is a device which removes the AC component but allows the DCcomponents of the rectifier to reach the load.

Ripples can be removed by one of the following filtering methods.(i) A capacitor, in parallel to the load, provides a easier bypass for the ripples due tolow impedance to AC at ripple frequency and leave the DC appear across the load.(ii) An inductor, in series with the load, prevents the passage of ripples due to highimpedance at ripple frequency, while allowing the DC due to low resistance to DC.(iii) Various combinations of capacitor and inductor, such has L-section filter, -section filter, etc., which make use of both the properties depicted above.Types of filter circuits:Depending upon the components used in the filter circuitsand the way they are connected, the filter circuits are classified as:(i) Shunt capacitor filter

(ii) Series inductor filter(iii) Choke-input (LC) filter(iv) Capacitor-input () filter.

37. List some advantages and disadvantages of CLC filters.

It can be used with both HWRs and FWRs. More output voltage is obtained. Output is almost pure DC.

38. What is the need for voltage regulators? What are the drawbacks ofunregulated power supply?An ordinary (unregulated) power supply from the following drawbacks:Poor regulation

The DC output voltage varies with the AC supply voltage which fluctuates atdifferent times of the day and is different at different locations.

The DC output voltage varies with temperature, in case semiconductors areused.

For certain applications the output of the filter even with small amount ofripples is not acceptable.

39. What is voltage regulator? List some types.

A voltage regulator is a circuit which makes the rectifier-filter output voltageconstant regardless of the variations in the input voltage or load.Types of regulators: There are three principal types of regulators, viz.,


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1. For normal operation, how is emitter-base junction biased?Forward.

2. For normal operation, how is collector-base junction biased?Reverse.

3. What is the relation between the currents of a transistor?IE =IB +IC

4. What are the types of circuit connections known as configurations, foroperating a transistor?

Common-Base (CB) Common-Emitter (CE) Common-Collector (CC)

5. What is the relation between and of a transistor ?

6. What are the regions used when BJT is used as a switch ?Saturation and cut-off regions.

7. What is the thermal resistance of power BJT ?Thermal resistance is the resistance to the flow of heat. Heat flows from the junctionto the surrounding air. Larger the transistor case, smaller the thermal resistance andvice-versa. Thermal resistance is reduced by providing heat sink with the transistor.

8. Why must the base be narrow for the transistor (BJT) action ?Beta () is the ratio of IC to IB .IB becomes less if the base width is narrow. Highervalue of can be obtained with lower value of base current.

9. What is the value of cut-in voltage for a BJT ?

For Silicon BJT - 0.7VFor Germanium - 0.3V


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10. Why an ordinary transistor is called bipolar ?Because the transistor operation is carried out by two types charge carriersmajority and minority carriers.

11. Why transistor (BJT) is called current controlled device ?The output voltage, current or power is controlled by the input current in atransistor. So , it is called the current controlled device.

12. What are emitter injection efficiency and base transport factor of atransistor?The ratio of current of injected carriers at emitter junction to the total emittercurrent is called the emitter injection efficiency.

Transport factor, = IcIB

13. Why silicon type transistors are more often used than Germanium type ?Because silicon has smaller cut-off current ICBO , small variations in ICBO due tovariations in temperature and high operating temperature as compared to those incase of Germanium.

14.Why collector is made larger than emitter and base?Collector is made physically larger than emitter and base because collector is todissipate much power.

15. Why the width of the base region of a transistor is kept very small as

compared to other regions?

Base region of a transistor is kept very small and lightly doped so as to pass most ofthe injected charge carriers to the collector.

16. Why emitter is always forward biased with respect to base?To supply majority charge carrier to the base.

17. Why collector is always reverse biased with respect to base?To remove the charge carriers away from the collector-base junction.

18. Why CE configuration is most popular in amplifier circuits?Because its current, voltage and power gains are quite high and the ratio of outputimpedance and input impedance are quite moderate.

19. Why is CC configuration seldom used?Because its voltage gain is always less than unity.

20. How many h-parameters are there for a transistor?Four hi, ho, hr hf or h11, h12, h21, h22.

21. What are the units for h11 and h22?h11 ohm; h22 mho (or) siemen.


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22. What are the parameters hr and h0 called?hr reverse transfer voltage.ho output admittance.23. Why h-parameters are called hybrid parameters?Because they have different units are mixed with other parameters.

24. Which is the smallest of the four h-parameters of a transistor?h0 or h12

25. What is the typical value of hie?1 k

26. A transistor connected in common base configuration has a -________input resistance and a ________ output resistance.Low input resistance.Very high output resistance.

27. Which of the BJT configuration is suitable for impedance matchingapplication and why?

CC configuration is suitable for impedance matching applications because of veryhigh input impedance and low output impedance.

28. Give the current gain expression for a common emitter transistorconfiguration?

= IE/IB

29. What are the tools used for small signal analysis of BJT?i. h Parameter circuit model.ii. z Parameter circuit model.iii. y Parameter circuit model.iv. Transconductance parameter circuit model.v. Physical model.vi. T-model.

30. What is the significance of ICBO and ICO?ICBO is the leakage current from the collector to base with emitter open. ICO is theleakage current from collector to emitter with base open (ICO = ICEO).


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31. Comparison of transistor connectionS.No

Characteristics Common Base Common EmitterCommonCollector

1. Voltage gain About 150 About 500 Less than 1

2. Input resistance Low (about 75) Low (about 750)Very high(about

750K)

3.Outputresistance

Very high (about 450K) High (about 45K)Low (about45)

4. ApplicationsFor high frequencyapplications

For audio frequencyapplications

Forimpedancematching

32. For a non-transistor IE = 12mA and = 140. Determine the value of IBand Ic.IE = 12mA, = 140

IB = IE/ (1+ )= 0.085mA

IE = IB + IC= 12 X 10-3/ (1+140)

IC = IE - IB = 12 - 0.085 X 10-3 = 11.915mA.

33. Differentiate FET and BJT (any two).

FET BJT1. Unipolar device (that is currentconduction by only one type of eitherelectron or hole).

1. Bipolar device (current conduction byboth electron and hole).

2. High input impedance due to reversebias.

2. Low input impedance due to forwardbias.

3. Gain is characterized by transconductance

3. Gain is characterized by voltagegain.

4. Low noise level 4. High noise level.

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

35. What is thermal runaway?The power loss in transistor is primarily at the collector junction because the voltagethere is high compared to the low voltage at the forward biased emitter junction. Ifthe collector current increases, the power developed tends to raise the junctiontemperature. This causes an increase in and further increase in collector current

in temperature may occur resulting in thermal run away.


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36. If the base current in a transistor is 30A and the emitter current is7.2mA. What are the values of , and Ic?

IB = 30A, IE = 7.2mA

37. 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 therequirements of a transistor in the active region. The collector current isexperimentally equal to the emitter current. Therefore the collector current will belarge as emitter current is large on the other hand, in CE operation IB is multipliedby , hence we get large collector current.

38. Why CE configuration is considered to be the most versatile one?The common emitter configuration provides very good voltage gain about 500CEconfiguration finds excellent usage in audio frequency applications, hence used inreceivers and transmitter.

39. Define bipolar junction transistors.

These devices operate with both holes and electrons and hence are called bipolarjunction.

40. Write the junction transistor operation may be drawn from the analysis.1. The major charge carriers in the PNP junction transistor are holes.

2. The major charge carriers in the NPN junction transistor are electrons

41. Write the range of parameter values for BJT. ParameterSymbol Range of value

1. Input resistance ri A few k

2. Current gain inCB mode

0.9 0.999

3. Current gain inCE mode

20 - 600

4. Output resistance r0 Tens of K5. Leakage current ICBO Na - A


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1. Why field effect transistor are called unipolar transistors?Because current conduction is by only one type of majority carriers.

2. Why FETs are so called? (or) Why FETs are voltage controlled devices?The output characteristics of a FET can be controlled by the applied electric field(voltage) and hence the name FET and are voltage controlled devices.

3. How is drain current controlled in a JFET?By controlling the reverse bias given to its gate, i.e., VGS.

4. What is the pinch-off voltage in a JFET?

The value of VDS at which the channel is pinched-off, i.e., all the free charges fromthe channel get removed, is called the pinch-off voltage in a JFET.

5. What are the parameters that control the pinch-off voltage of JFET?Electron charge, donor/acceptor concentration density, permittivity of channelmaterial and half-width of channel bar.

6.How does the FET behave (i) for small values of |VDS| and (ii) for largevalues of |VDS| ?(i) FET behaves as an ordinary resistor for small values of |VDS|, i.e., in ohmic

region.(ii) FET behaves as a constant current source for large values of |VDS| till breakdownoccurs.

7. What is meant by saturation region?The region of drain characteristic of a FET in which drain current remains fairlyconstant is called the saturation or pinch-off region.

8. What is meant by drain-source saturation current IDSS?The drain current in pinch-off region with VDS = 0 is called IDSS.

9. Why is the input impedance of FET very high?Because its input circuit (gate-to-source) is reverse biased and the input gate currentis very small (nA).

10. Why MOSFET is called IGFET?MOSFET is constructed with the gate terminal insulated from the channel. So it iscalled as insulated gate FET or IGFET

11. Why E-MOSFET is called sometimes normally-off MOSFET? E-

MOSFET operates with large positive gate voltages only and does not conduct whenVGS = 0. So, it is called normally-off MOSFET.


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12. What is meant by gate-to-source threshold voltage VGST in E-MOSFET?It is the minimum value of VGS that is required to form the inversion layer.

13. Why MOSFETs are never connected or disconnected in the circuit whenpower is ON?If a MOSFET is connected or disconnected in a circuit when power is ON, thetransient voltages caused by inductive kickback and other effects may exceedVGS(max) and thus wipe out the MOSFET.

14. Name the factors which make the JFET superior to BJT?High input impedance, low output impedance and low noise level.

15. List the JFET parameters.Transconductance (gm), drain resistance (rd) and amplification factor () = gmrd

16. Give the drain current equation of JFET?

ID= IDSS (1 )

2

17. List some applications of JFETs.

Used as buffers in measuring equipment, receivers and other general purposedevices.

Used in RF amplifiers of FM tuners and communication equipment. Used in mixer circuits in FM and TV receivers and communication equipment. Used in cascade amplifiers in measuring and test equipment.

Used as voltage variable resistor (VVR) in OP-AMPs and tone controls. Used in hearing aids and inductive transducers. Used in oscillator circuits. As the physical size is small, it finds use in digital circuits in computers, large

scale integration (LSI) and memory circuits. Used as current sources.

18. List some advantages of MOSFETs.MOSFETs combine the inherent advantages of solid-state devices such as: Small size Low power consumption Simplicity of construction Mechanical ruggedness.

With the inherent advantages of electron tubes such as:

Very high input impedance Square law transfer characteristics.

19. In a JFET, gate-source junction is always biased and source-drain is .. biased.Reverse, Forward

20. How does the transconductance vary with drain current in a JFET?In a JFET, the transconductance gm varies with the drain current ID by the followingequations.


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gm =

21. Define JFET

A Junction field effect Transistor is a three terminal semiconductor device in whichcurrent conduction is by one type of carrier (i.e., either electron or holes)

22. Define channel.

It is a bar like structure which determines the type of FET. Different types of Nchannel are FET and P channel FET.

23. Explain the biasing of JFET.

Input is always reverse biased and output is forward biased. (Note: In transistorinput is forward biased and output is reverse biased).

24. Define Drain resistance.

It is the ratio of change in Drain source voltage (VDS) to the change in Draincurrent (ID) at constant gate source voltage (VGS).

25. Define Transconductance.

It is the ratio of change in drain current (ID) to the change in Gate Source

Voltage (VGS) at constant Drain Source voltage(VDS)

26. Write down the formula for Amplification factor.Drain resistance X Transconductance = Amplification factor.

= Ro X gm

27. Write the advantages of JFET.

1. Input impedance of JFET is very high. This allows high degree of Isolation betweenthe Input and Output circuit.2. Current carriers are not crossing the junction hence noise is reduced drastically


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28. List the JFET parameters.

1. A.C drain resistance (rd)2. Transconductance (gm)3. Amplification factor ()

29. Mention the two types of field effect transistors,

1. N-channel FET2. P-channel FET

30. Define pinch off voltage.

As the reverse bias is further increased, the effective width of the channel decreases,

the depletion region or the space charge region widens, reaching further into the

channel and restricting the passage of electrons from the source to drain. Finally at a

certain gate to source voltage VGS = VP.

31. Explain the depletion node of operation in MOSFET.

When the gate is at negative bias, the thickness of the depletion layer furtherincreases owing to the further increase of the induced positive charge. Thus the draincurrent decreases, as the gate is made more negative. This is called depletion modeof operation.

32. Explain the term Drain in FET.

The drain is the terminal through which the current leaves the bar. Conventioncurrent entering the bar is designated as ID.

33. Explain the terms source in FET.

The source is the terminal through which the current enters the bar. Conventionalcurrent entering the bar is designated as IS.

34. Define the term Gate in FET.

The gate consists of either P+ or N+ impurity regions, heavily doped and diffused tothe bar. This region is always reverse biased and in fact, controls the drain currentID.

35. Write the relative disadvantages of an FET over that of a BJT.

1. The gain bandwidth product in case of a FET is low as compared with a BJT.2. The category, called MOSFET, is extremely sensitive to handling therefore

additional precautions have to be considered while handling.


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36. Mention the methods used for biasing circuits in FET.

1. Self-bias.2. Potential divider bias.

37. Mention the methods between FETs and MOSFETs.

Symbol JFET MOSFET

gm 1000 to 25,000 mhoms 1000 to 20,000 pmhog

rd 0.1 to 1M 1 to 50KIGSS 0.1 to 10nA 0.1 to 10nA-ras >109 >101313

Crss or Cgd 1 to 4Pf 0.005 to 1Pf


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1. What is a differential amplifier?An amplifier, which is designed to give the difference between two input signals, iscalled the differential amplifier.

2. What is the function of a differential amplifier ?

The function of a differential amplifier is to amplify the difference of two signalinputs,

i.e., where Ad is the differential gain

3. When two signals V1 and V2 are connected to the two inputs of adifference amplifier, define a difference signal Vd and common-mode signalVcThe difference signal Vd is defined as the difference of the two signal inputs,i.e., Vd = V1 V2The common-mode signal Vc is defined as the average of the two signals,I.e., Vc =1/2 (V1 + V2)

4. What is the differential-mode voltage gain of a differential amplifier?It is given by Ad = (A1-A2)

5. What is the common-mode gain AC in terms of A1 and A2?It is given by Ac = A1 + A2

6. Define CMRR.The common-mode rejection ratio(CMRR) of a differential amplifier is defined as theratio of the differential-mode gain to common-mode gain.CMRR = |Ad|Ac|

7. What are the ideal values of Ad and Ac with reference to the differential

amplifier?Ideally, Ac should be zero and Ad should be large, ideally infinite.

8. Express CMRR in d B.CMRR (dB) = 20 log Ad 20log Ac.

9. What are advantages of differential amplifier?It has high gain and high CMRR.

10. List some applications of differential amplifiers?

Used in IC applications, AGC circuits and phase inverters.


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11. Define (i) feedback (ii) positive feedback and (iii) negative feedback.

i. Feedback: The process of combining a fraction of the output (of a Device-amplifier) back to its input is called feedback.

ii. Positive Feedback:If the feedback is in phase to the input, it is called positivefeedback. Here

iii. Negative Feedback:When the feedback is in opposition (out of phase) to theinput, it is called negative feedback. Here

12. What loop gain of a feedback amplifier.In a feedback amplifier, when the signal passes through an amplifier

13. Mention the four connections in Feedback.1. Voltage series feedback.2. Voltage shunt feedback3. Current series feedback.4. Current shunt feedback.

14. Explain the voltage series feedback.In this case, the feedback voltage is derived from the output voltage and fed inseries with input signal. The input of the amplifier and the feedback network are inseries is also known as series parallel in parallel, hence this configuration is also

known as series parallel feedback network.

15. Explain the voltage shunt feedback.The input of amplifier and the feedback network are in parallel and known as parallelparallel feedback network. This type of feedback to the ideal current to voltageconverter, a circulating having very low input impedance and very low outputimpedance.

16. Explain the current series feedback.When the feedback voltage derived from the load current and is fed in series with the

input signal, the feedback is said to be current series feedback, the inputs of theamplifier and the feedback network are in series and the output are also in series.This configuration is also called as series-series feedback configuration.

17. Explain the current shunt feedback.When the feedback voltage is derived from the load current and a fed in parallel withthe input signal, the feedback is said to be current shunt feedback. Herein the inputsof the amplifier and the feedback network are in parallel and the outputs are inseries. This configuration is also known as parallel series feedback18. Write the effects of negative feedback.

1. The gain becomes stabilized with respect to changes in the amplifier active deviceparameters like hfe.2. The non-linear distortion is reduced there by increasing the signal handlingcapacity or the dynamic range of the amplifier.


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19. Write the conditions for a circuit to oscillate.1. The oscillator circuit should consist of an amplifier and a portion of the outputshould be feedback to the input. For sustained oscillations, the feedback voltagemust be in phase with the input, i.e., total phase shift around the loop must be 360.2. The amount of energy or power feedback to the input must be sufficient to theinput circuit.

20. Mention the classification of oscillators.According to the frequency determining networks,1. RC oscillators2. LC oscillators3. Crystal oscillators

21. List the advantages of phase shift oscillator.1. The phase shift oscillator does not required conductance or transformers.2. It is suitable for the low frequency range i.e., from a few hertz to several hundredKHz. The upper frequency is limited because the impedance of RC network maybecome so small that it loads the amplifier heavily.

22. Write the disadvantages of Phase shift oscillator.1. It is necessary to change the C or R in all the three RC networks simultaneouslyfor changing the frequency of oscillations. This is practically difficult.2. It is not suitable for high frequencies.

23. Write the main drawback of LC oscillators.

1. The frequency stability is not very good.2. They are too bulky and expensive and cannot be used to generate lowfrequencies.

24. Define Piezo electric effect.Certain crystal, when suitable wt, develop a potential difference between oppositefaces, magnitude and polarity of which depends on pressure or tension applied to theother pair of perpendicular faces. This effect is called Piezo electric effect.

25. Define differential amplifier.

When two or more input is applied to the amplifier and receive the single output iscalled differential amplifier.VO = V1 - V2


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26. Define stability.The variation of input is applied to the system; to get the constant output is calledstability.

27. Define switch.A switch is a device which opens or closes the electrical circuit, i.e., can turn on oroff current in an electrical circuit. An ideal switch has zero internal resistance when itis closed an infinite leakage resistance when it is open


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1. Define pulse and pulse circuits.The word pulse is applied to waveforms that exist for a very short period. The word pulse circuits refer to the active and passive circuits intended to handle, generate,shape and sotre pulse signals.

2. Define switching circuit.A circuit which can turn ON or OFF the current in the electronic circuits is calledswitching circuit

3. Define wave shaping and wave shaping circuits.

The process of generating new wave shapes from older wave forms using somenetword is called wave shaping. The circuits which perform wave shaping are calledwave shaping circuits.Eg: Clippers, Clampers, Integrator, Multipliers, etc.

4. Give some examples of linear and non-linear wave shaping circuits.

Linear wave shaping circuits use R,L,C.Examples: RC, RL, RLC circuits, Integrator, Summer, etc.

Non-linear wave shaping circuits uses R,L,C diodes,Examples: Clippers, Clampers, etc.

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

Because of the blocking property of the capacitor for DC or low frequency inputsignals, the capacitor acts like an open circuit and blocks the signal. So the capacitorin high-pass RC circuits is called blocking capacitor.

6. Why a high-pass RC circuit is called differentiator?

Because it gives the output voltage proportional to the differentiation of inputvoltage.

7. What are the conditions for a series RC circuit to act as a differentiator?i. RC Time constant


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8. List the applications of high-pass RC circuits. To generate a step from ramp input. To generate a square wave from a triangular wave. To generate a series of narrow pulses called pips from rectangular or square

waves. Used in R-C coupling of amplifiers where distortion and differentiation of

waveform is to be avoided.

9. Why a low-pass RC circuit is called an integrator?Because it gives the output voltage proportional to the integral of input voltage.

10. What are the conditions for a series RC circuit to act as an integrator?

i. RC >>Tii. R >10 XC

11. List the applications of low-pass RC circuits. Used as bypass capacitors. To perform mathematical integration in analog computers. To generate triangular and ramp waveforms. Used to discriminate pulses of different lengths.

12. What are the characteristics of pulse waveforms?

Rise time, fall time and tilt.

13. Define Clamping.Clamping is the process of shifting the input signal above or below the zero level. Byclamping the input signal suitably, we can introduce (insert) any required DC levelinto the signal. So clapmers are also called DC level restorers.

14. What is a Clamper?The circuit with which the waveform can be shifted, such that, a particular part of it(say positive or negative peak) is maintained at a specified level, is called a

clamping circuit or simply, clamper.

15. List the types of Clampers. Positive Clamper Negative Clamper Biased Clamper


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16. What is the function of a positive clamperIt shifts the signal towards the positive side such that the negative side of the signalreduces to zero.

17. What is the function of a negative clamper?It shifts the signal towards to negative side such that the positive side of the signalreduces to zero.

18. What is biased clamper?A biased clamper means that clamping can be done at any voltage level other thanzero.

19. List the applications of Clampers.

They are used in T.V. receivers to restore the original DC reference signal(correspondiong to the brightness level of the picture) to the video signal.

They are used to produce a DC voltage is a multiple of peak AC input voltage i.e.,they are used a as voltage multipliers.

They are used to supply power to high voltage/low current devices like CRTs usedin T.V receivers, CROs and computer displays.

20. What is a clipper?The circuit with which the waveform is shaped by removing (or clipping) a certainportion of the input signal voltage above or below a present level is called clippingcircuit or simply, clipper. They are used to limit the amplitude of the input signal.

21. List the types of clipers.Based on limiting action:

Positive Clipper Negative Clipper Biased Clipper Combination Clipper

22. What is the difference between the output from a clipper and a clamper?The output of a clipper appears as if a portion of the input signal were clipped off,but a clamper simply shifts the input to a different DC level.

23. What is the difference between positive and negative clippers?The positive clippers removes the positive half cycles, while the negative clipperremoves the negative half cycles, of the input waveform.

24. What is the difference between positive and negative clampers?A positive clamper pushes the signal on the positive side or upward while a negativeclamper pushes the signal on the negative side or downward.

25. A clamper circuit sometimes uses a DC battery in addition to diode, acapacitor and a resistor. Why? = To cause an additional shift.


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26. How does a clamper affect the peak-to-peak and RMS values of awaveform? = No change.

27. List the applications of clippers. They are used to remove unwanted portions like noise accumulated on peaks

of waveforms. They are used in T.V receivers to separate since pulses from the composite

video signal. Two level clippers are used as square wave generators. They are used in PPM modulators.

28. What is a multivibrator? List the different types of multivibrators.A Multivibrator is basically a two stage amplifier with 100% feedback between thetwo stages such that output of one is fed back to the other.The feedback from one stage to the other is so arranged that when one transistor isdrive to cut-off, the other is driven to saturation. Thus at any particular instant oftime, one transistor is ON and the other is OFF.TypesThere are three basic types of multivibrators depending on the type of couplingnetwork used. They are: Astable multivibrators (AMV) or free running generator. Monostable multivibrator (MMV) or one-shot multivibrator or univibration. Bistable multivibrator (BMV) or flip-flop. An AMV uses capacitive coupling. An MMV uses RC coupling. An BMV uses resitive coupling.

29. What is AMV? Why is it called a square wave generator?An AMV is essentially a two-stage RC coupled amplifier with output of one stagsupplied back to the input of another stage.An AMV generates square wave of known frequency (or period). So, it is called asquare wave generator.

30. How does a MMV circuit be constructed from a AMV?By replacing one R-C timing circuit by a DC voltage divider.31. What is the function of commutating capacitors in multivibrator?

To improve the switching characteristics of the circuit.

31. Why are mnostable Multivibrators called one-short Multivibrators?They generate one output pulse for every trigger pulse and hence the name oneshot Multivibrators or univibrators.

32. Whey the BMV is called a flip-flop?In a BMV, one trigger pulse causes the Multivibrator to flip from one state to theother state and the next pulse causes it to flop back to its original state. So, it is

called the flip flop.


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33. What are the applications of AMVs?AMVs are used as

Square wave generators. Voltage to frequency converters. Pulse synchronization circuits Clock for binary logic signls.

34. What are the applications of MMVs?MMVs are used for

Generation of well defined pulses Logic design of pulse delay Variable pulse width

35. What are the applications of BMVs?BMVs are used asMemory elements in shift registers, counters, etc.,

36. Write the application of Bistable multivibrator.1. The bistable multivibrator is used as memory element in shift registers counters,and so on.2. It is used to generate square waves of symmetrical shape by sending regulartriggering pulses to the input. By adjusting the frequency of the input triggerpulse,the width of the square wave can be altered

37. What are the applications of Schmitt trigger? Amplitude comparator Squaring circuit Flip flop

38. Why an AMV is called free running relaxation oscillator?Because it runs and relaxes alternately.

39. Which portion of the UJT characteristic is used to make UJT to generatesawtooth waves?Negative resistance region.

40. Give the formula for pulse repetition frequency of UJT based sawtoothgenerator? ( )

41. What is the function of Clamper circuit?Clamper circuit introduces a d.c level to an a.c signal. Hence, the damper circuit ornetwork is also known as d.c restorer. These circuits find applications in televisionreceivers to restore the d.c reference signal to the video signal.


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42. Define rise time.The time during which the voltage or current reaches to a maximum positive ornegative value is called the rise time. The rise time is zero for the square wave.

43. Define sinusoidal waveform.A sine wave varies continuously in amplitude in proportion to the sine of an anglewhich varies from o to 360.

44. Define market pips.Circuits make use of the transient properties of R, C and l to realize themathematical operations of differentiations, integration and summation. Thedifferentiating circuit is extensively used to convert summation. The different circuitis extensively used to convert pulse trains to a series of timing pips known as marketpips.

45. Mention the classification of switches.1. Mechanical switch.2. Electronic switch.

46. Define ramp function generator.The shape of the pulse resemble the teeth or a saw, therefore the name saw toothwaveform. A saw tooth generator is also called ramp function generator.

47. Define Multi vibrators.There is a class of RC coupled oscillators called Multivibrators which generate non-sinusoidal waveforms such as triangular square and sawtooth.

48. Define free running multi vibrators.A Multivibrator is a form of relaxation oscillators. They may need no externalexcitation, i.e., they are self-excited; if so they are termed as free runningMultivibrator.

49. Mention the types of Multivibrators.1. Monostable multivibrator.2. Bistable multivibrator.3. Astable multivibrator.

50. Define Astable multivibrator.The change in the output state is regenerative. The output never remainspermanently at a particular state. Hence, this multivibrator is called astablemultivibrator.

51. Define bistable multivibrator.Since in the absence of an external signal, either transistor can continue indefinitelyin ON or OFF state, they are equally stable in both staes. Therefore, the nameBistable multivibrator.


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52. Define Monostable multivibrator.It is also called the one shot multivibrator. The one shot multivibrator is driven, it isnot free running unlike the bistable trigger, the monostable has one stable state towhich it returns after the eternal driving pulse has caused it to execute its cycle.

53. Define Schmitt Trigger.When the input is sinusoidal signal and converted to square waveform in output iscalled Schmitt trigger. Generation of pulses when the voltage level rises to a certainvalue is achieved by using a circuit.

54. Define high pass filter.At very high frequencies the capacitor acts as a virtual short circuit and the outputfalls to zero. Hence this circuit passes the low frequencies of the input andattenuates the high frequency is called low pass filter.

56. Define duty cycle.It is the ration of the ON period to the total period.(T = TON + TOFF)Therefore, Duty cycle = TON/ T

57. Write the application of Astable Multivibrator.1. The astable multivibrator is used as square wave generator, voltage to frequencyconvertor and in pulse synchronization, as clock for binary logic signals and so on.2. Since it produces square waves it is a source of production of harmonicfrequencies of higher order,

58. If an astable multivibrator has C1 = C2 = 1000PF and R1 = R2 = 20K.Calculate the frequency of oscillation.The frequency of a symmetrical astable multivibrator

59. Write the applications of monostable multivibrator.1. The monostable multivibrator is used to function as an adjustable pulse widthgenerator.2. It is used to generate uniform width pulses from a variable width input pulse train.

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