Hi friends today we are posting the Microprocessor Viva question and answers. You can visit the below download link and you can download a PDF version of the FAQ set based on microprocessor, the set contains more than 100 question with answer. As the exams is coming very near and many students wants the Frequently Asked Questions (FAQ) on the lab specially for the external purpose. Actually most of the students don't want to give the answer as they don't know, but giving not the answer of even a single question mayn't affect your IA, but same can affect your external, even if you executed the program.
So, in this set we have some basic ques as well so simply go through it, and if it isn't sufficient for you then follow your book.:) But the given ques are more than sufficient. I have searched all over the net for the different ques's answers. so go through it.
Here, we are posting VLSI lab viva question with answers for 7th semester Electronics and Communication Students.You can Download it for free. Here is Download link, it'd in PDF form of 55 pages. There are several other question also in this manual so avoid unnecessary Question, and read only those questions which suits you more according to your lab and lab manual.
It also consists some HDL lab viva questions, so avoid that questions or if you have time then, you can also go through that.
Level of Some questions are very high, so don't read that, as that is for M.Tech Students. Click on below Download link to Download the Question & Answers For VLSI Lab.
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Last Updated on: 7/11/2012 at 7:36AM
Power electronics is one of the important branch of electronics and electrical engineering. It delas with conversion and control of electric energy.
Q2. What are main applications of Power electronics?
Power supplies is Computers, medical equipments, Communication systems, telephone exchange, Satellite systems etc.
Power control in resistance welding, induction heating, electrolysis process and etc,
Power conversion for HVDC and HVAC transmission systems.
Q3. What is SCR?
Silicon Control Rectifier (SCR) belongs to the thyristor family, it is three terminal four layer PNPN diode.
Q4. What are merits and applications of SCR?
Merits:
i) Very small amount of gate drive is required.
ii) SCR’s with high voltage and current ratings are available.
iii) On-state losses in SCR’s are reduced.
Applications:
i) SCR’s are best suitable for controlled rectifier.
ii) AC regulators, lighting and heating applications.
iii) DC motor drives, large power supplies and electronic circuit breaker.
Q5. What is TRIAC?
TRIAC can be considered as antiparallel SCR. TRIAC conducts in both the directions and it has single gate.
Some Important Points:
i) All the power electronic devices are used as on/off switches.
ii) Power converter converts input power in the form suitable for load.
iii) All power devices are solid state. Hence they are called power electronic devices.
Q6. Differentiate between SCR and BJT.
SCR:
i) Four layer PNPN device.
ii) Turns on by regeneration.
iii) Gate has no control once SCR is turned on.
iv) External circuits are required to turn off the SCR.
v) Switching frequencies are low.
BJT:
i) Three layer (PNP or NPN) device.
ii) No regeneration exists.
iii) Base has full control over the operation of BJT.
iv) No external circuits are required. BJT turns off if base drive is removed.
v) Switching frequencies are high.
Q7. What are the differences between BJT and MOSFET?
BJT:
i) This is bipolar device.
ii) Controlled by base.
iii) Current controlled device.
iv) Negative temp coefficients.
v) Losses are low.
MOSFET:
i) This is majority carrier device.
ii) Controlled by gate.
iii) Voltage controlled devices.
iv) Positive temp coefficients.
v) Losses are high than BJT’s.
Q8. What are the different ways to Turn-on and Turn-off the Thyristor.
Q9. What is turn0on and turn-off time of a thyristor?
Turn-on: it is defined as the time from initiation of gate drive to the time when anode current reaches to its full value.
Turn-off time: it is the time required to achieve forward blocking capability after commutation is initiated.
Q10. List the thyristor current and voltage ratings.
Current ratings:
i) Average current rating.
ii) RMS current rating.
iii) Surge current rating.
iv) I2t rating.
v) Di/dt rating.
Voltage ratings:
i) Peak repetitive forward blocking voltage.
ii) Peak repetitive reverse voltage or peak inverse voltage(PIV).
iii) Non-repetitive peak reverse voltage.
iv) Dv/dt rating.
Q11. What is DIAC, and why it used?
The DIAC is the two terminal and four layer device. It is mainly used for triggering TRIAC’s. it conducts in either direction. It is low power triggering device, and there are no control terminal on the DIAC.
Q1. What are the difference between transistor and SCR?
1. SCR is four layer PNPN device, whereas transistor is three layer (PNP or NPN) device.
2. SCR turns on by regeneration but there is no regeneration in BJT.
3. Gate has no control over the conduction once SCR turns on. BJT can be turned off by base drive.
4. BJT’s have higher switching frequencies than SCR’s.
Q2. Explain latching current and holding current of the thyristor?
Latching current: It’s the minimum forward current that flows through the thyristor to keep it in forward conduction mode at the time of triggering. If the forward current is less than latching current, thyristor doesn’t turn on.
Holding Current: It is the minimum forward current that flows through the thyristor to keep it in forward conduction mode. When forward current reduces below holding current, thyristor turn off.
Q3. What are the advantages of MOSFET’s over BJT’s?
i) MOSFET’s have simpler gate drive circuits.
ii) They have high switching frequencies.
iii) MOSFET’s are majority carrier devices.
iv) MOSFET’s have positive temperature coefficients.
Q4. Why pulsed gate drive is used for SCR?
Once SCR is turned on, gate drive is no more required. Hence if pulsed gate drive is used, SCR turns on at particular pulse. The remaining pulses are not used. But pulsed drive reduces losses in gate cathode of the SCR.
Q5. Define the delay angle of phase-controlled rectifier.
It is the angle at which thyristors are triggered after zero crossing. After zero crossing of supply voltage, one pair of thyristor is forward biased. After delay angle (α), the SCR’s are triggered.
Q6. Why is power factor of semiconverter better than full converter?
The output voltage of semiconverter doesn’t go negative. Hence it’s reactive power is reduced. Where as output voltage of full converter goes negative. Hence it’s reactive power is more. Therefore power factor of semiconverter is better than full converter.
Q7. What are the differences between freewheeling diode and feedback diode?
Freewheeling diode is used to circulate the load energy in the load itself. Feedback diode is used to transfer the load energy to the source. Feedback diode is normally used in inverters. Freewheeling diode is normally used in controlled rectifiers.
Q8. What is inverting operation of the converter?
Converters are basically AC to DC controlled rectifiers. The power flows from AC supply to DC load. In inverting operation, the power flows from DC load to AC supply. Under such situation, the DC load is normally a battery. Thus the power of DC battery load is given to AC supply through controlled rectifier. For this operation, firing angle is greater than 90˚.
Q9. What are control strategies of chopper?
Choppers have following control strategies:
1. Fixed frequency operation: in this type of control, the frequency of chopper remains fixed , but on and off periods of chopper change as per the duty cycle.
2. Variable frequency operation: in this type of control, the on or off period remains fixed. Hence frequency of the chopper changes when duty cycle is changed.
3. Current limit control (CLC) : in this type of control, the output is sensed, when output current falls below reference level, chopper is turned on. And when output current rises above reference level, chopper is turned off.
Q10. Explain the use of step-up chopper.
Step-up chopper is normally used for energy transfer. The load energy is transferred to source by step-up operation.
Q11. What is four quadrant chopper?
Four quadrant chopper operates in all the four quadrants of Vo – Io plane. It can perform forward and reverse motoring as well as forward and reverse regeneration.
Q12. What is the main difference between voltage source inverter and current source inverter?
1. In the voltage source inverter, input voltage remains fixed and current varies according to load variations. But in current source inverter, input current remains fixed and voltage varies according to the load.
2. In voltage source inverters, short circuit of the devices can damage them. In current source inverter short circuit cannot damage the circuit.
3. Voltage source inverters need freewheeling diodes. But current source inverters doesn’t need freewheeling diodes.
Q13. What are PWM inverters?
PWM inverters are basically pulse width modulated inverters. Voltage control in such inverters is achieved by varying width of the pulse. In one half cycle there can be single or multiple pulses. Number of pulses determine lowest order harmonic present in inverter output voltage. Thus PWM inverters provide voltage control as well as harmonic reduction simultaneously.
Q14. What is cycloconverter?
Cycloconverter is AC to AC converter. It has 1ф or 3 ф AC input. Output is variable voltage and variable frequency. Cycloconverters are used for induction motor drives. They have an advantages of variable frequency output over other AC voltage.
Q15. What are the advantages and disadvantages of AC voltage controller?
Advantages:
1. They use line communication, hence no extra communication circuits are required.
2. They have high efficiencies since device losses are reduced.
Disadvantages:
1. Large ripple and harmonics are present in the output.
2. Output waveforms are not sinusoidal.
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Ans: Multiplexing is method by which multiple analog message signals or digital data streams are combined into one signal over a shared mediuANSWER Q2. What are different types of multiplexing?
Ans: i) Space-division multiplexing (SDM)
ii) Frequency-division multiplexing (FDM)
iii) Time-division multiplexing (TDM)
iv) Code-division multiplexing (CDM)ANSWER Q3. What is TDM?
Ans: TDM is the process of dividing up one communication time slot into smaller time slots.
OR, It is the technique of separating the signal in time is called TDM.
ANSWER Q4. What do you mean by FDM?
Ans: Frequency division multiplexing is the technique of separating the signal in frequency is reffered as FDM.
ANSWER Q5. What is Amplitude shift Keying (ASK) ?
Ans: It is a type of digital modulation in which, the digital data modulates amplitude of the carrier.
ANSWER Q6. What are different types of digital modulation?
Ans: i) Phase shift keying (PSK)
ii) Frequency shift keying (FSK)
iii) Amplitude shift keying (ASK)
ANSWER Q7. What is Phase shift keying ( PSK)?
Ans: In this technique, the digital data modulates the phase of the carrier.
ANSWER Q8. What is Frequency shift keying (FSK) ?
Ans: In this technique, the digital data modulates the frequency of the carrier.
ANSWER Q9. What is Binary Phase shift Keying (BPSK) ?
Ans: In BPSK, binary symbol ‘1’ and ‘0’ modulate the phase of the carrier.
ANSWER Q10. What is bandwidth of BPSK signal?
Ans: BW=2fb. where fb=1/Tb.
ANSWER Q11. What do you mean by Differential Phase Shift Keying (DPSK)?
Ans: DPSK is differentially coherent modulation method. It does not need a coherent carrier at the demodulator. The input sequence of binary bits is modified such that the next bit depends upon the previous bit. In DPSK the phase of the carrier changes only on symbol ‘1’, while in BPSK, phase of the carrier get changes both at ‘1’ and at ‘0’. So this is the major difference between DPSK and BPSK.
ANSWER Q12. What is Bandwidth of DPSK?
Ans: BW= fb.
ANSWER Q13. Show the phase change in DPSK at the digital input 10111101.
Ans: Draw it by yourself with help of your textbook.ANSWER Q14. What is QPSK?
Ans: Quadrature phase shift keying (QPSK) also known as 4-PSK, so the phase get changed at four different point or angle and that is at 45, 135,225 and 315O at the digital input 00,10,11,01 respectively.
ANSWER Q15. Why JK flip-flop is being used in this type if Keying?
Ans: JK flip-flop is used in this type of keying in order to separate the even an odd bits according to the digital inputs.
ANSWER Q16. What are the advantages over other types of keying?
Ans: i) The BW required by QPSK is just half of the BPSK.
ii) The information transmission rate is higher.
iii) Carrier power remains constant.
ANSWER Q17. What is a GUNN DIODE?
Ans: Gunn diode is a bulk semiconductor device, normally made up of N-type semiconductor.
ANSWER Q18. How would you find the propagation loss for two different known length and voltage of optical fiber.
Ans: Propagation loss= 10/(L1-L2) log V2/V1 .
Where L1,L2 are length of two different optical fiber and V2 and V1 are the voltages across it.
ANSWER Q19. What is the used formula to find out the bending loss for an optical fiber?
Ans: There is no any fixed formula to find so, bending loss is the relation between the voltages (V) to the diameter (d) of bended optical fiber. ANSWER
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Ans: : i) Immediate addressing mode
ii) Register addressing mode
iii) Direct data addressing mode
iv) Register-indirect addressing mode
v) Register-relative addressing mode
vi) Base indexed addressing mode
vii) Base relative + indexed addressing .
ANSWER Q5. How many byte of instruction is used in Direct addressing mode?
Ans: 3 byte instruction.
ANSWER Q6. How many bytes of instruction is used in displacement addressing?
Ans: 4 byte instruction.
ANSWER Q7. For the given set of instruction give the mode of operation.
MOV BL, 44H
MOV BX, NUMBER
MOV CX, [BX]
MOV AX, [BX+1000H]
MOV DX, [BX+DI]
Ans: i) Immediate addressing
ii) Displacement addressing
iii) Reg. Indirect addressing
iv) Reg. relative addressing
v) Base indexed addressing.
Q8. How execution time of an instruction can be determined?
Ans: The execution time of an instruction can be determined by multiplying the number of clock cycles needed to execute the instruction by the clock periods.
Ans: XLAT: The translate instruction is used for finding out the ports in case of code conversion problems using look-up table technique.
LEA: Stands for Load Effective Address, The load effective address instruction loads the effective address formed by destination operand into the specified source register.
ADC: Add along with carry.
INC: Increment by 1.
ANSWER Q10. Explain unsigned multiplication byte or Word.
Ans: This instruction multiplies an unsigned byte or word by the contents of AL. The unsigned byte or word may be in any one of the general purpose register or memory location. It can do 8,16-bit multiplications.
Used character is ‘MUL’.
ANSWER Q11. What is difference between directive and instructions?
Ans:
Directive /Instruction
1. Do not get converted into machine language. /Will get converted into machine language.
2. Hint to assembler to do some task. /Indication to the proccessors.
ANSWER Q12. Define the meaning of given program words.
DB, DQ, DT, DW, PROC, ENDP
Ans: DB: define byte
DQ: Define quard word.
DT: Resume to byte of memory location .
DW: Reserve two memory location.
PROC: To call a subroutine (Procedure)
ENDP: End the procedure.
Ans: The directive EXTRN informs the assembler that the names procedures and labels declared after this directive have already been defined in some other assembly language module. While in the other modules where the name procedure and labels actually appear, they must be declared PUBLIC using PUBLIC directive.
ANSWER Q14. Give the difference between Procedure and Macros.
Ans:
Procedure
Macros
Accessed by CALL & RET instruction during program execution.
Accessed during assembly with name given to MACRO when defined.
Machine code for instruction put only once in the memory.
Machine code is generated for instruction each time when MACRO is called.
With Procedure less memory is required.
With MACROS more memory is required.
Parameters can be passed in registers, memory, or stack.
Parameters passed in port of statement which calls MACROS.
Q1. What is difference between microcontroller and microproccessor?
Ans:
Microproccessor
Microcontroller
Memory, ports, timers, interrupts and controllers are external to the chip.
Memory, ports, interrupts and controllers are internal to the chip.
Based on Von-Neumann architecture.
Based on Harvard architecture.
Have many instructions for data transfer b/w the microprocessor and external memory.
Have limited instructions for data transfer b/w the microcontroller and external memory.
The instruction sets contains limited number of instructions for bit operation.
It performs large number of bit level operation.
ANSWER Q2. What are flags and Program status word (PSW)?
Ans: Flags are 1-bit registers provided to store the result of certain program instructions.
PSW: The PSW contains the math flags, user program flag F0, and the register select bits that identify which of the four general purpose register banks is currently in use by the program.
CY
AC
F0
RS1
RS0
OV
--
P
ANSWER Q3. What is stack?
Ans: The stack refers to an area of internal RAM that is used in conjugation with certain opcodes to store and retrieve data quickly.
ANSWER Q4. What is counter and timer?
Ans; Counter is the process of counting the pulses generated by any system.
ANSWER Q5. Explain the TCON special function register?
Ans: TCON special function register
TF1
TR1
TF0
TR0
IE1
IT1
IE0
IT0
Explain the above table based on your microcontroller knowledge of flags1 and 0’s and others.
ANSWER Q6. Explain TMOD special function register.
Ans: TMOD special function register
Gate
C/Tbar
M1
M0
Gate
C/Tbar
M1
M0
ANSWER Q7. Draw the special function register for SCON and PCON.
Ans: SCON
SM0
SM1
SM2
REN
TB8
RB8
TI
RI
PCON:
SM0D
--
--
--
GF1
GF0
PD
IDL
ANSWER Q8. What do you mean by timer flag interrupt?
Ans: When a timer/counter overflows, the corresponding timer flag, TF0 or TF1, is set to 1. The flag is cleared to 0 when the resulting interrupt generates a program call to the appropriate timer subroutine in memory.
ANSWER Q9. Draw and explain the Interrupt enable (IE) and Interrupt Priority (IP) special function register.
Ans: IE special function register:
EA
--
ET2
ES
ET1
EX1
ET0
EX0
IP special function registers:
--
--
PT2
PS
PT1
PX1
PT0
PX0
- not implemented
PT2: Reserved for future use.
PS: Priority of serial port interrupt.
PT1: Priority of timer of 1 overflow interrupt. Set cleared by program.
PX1: Priority of external int 1.
PT0: Priority of timer 0 overflow interrupt.
PX0: Priority of external int 0.
ANSWER Q10. What are different addressing modes in microcontroller? Give one example for each.
Ans: 1. Immediate addressing mode. (ADD A, #77)
2. Register addressing mode. (ADD A, R0)
3. Direct addressing mode. (MOV A, 088H)
4. Indirect addressing mode. (MOV A,@R0)
ANSWER Q11. What are different instruction sets?
Ans: 1. Data transfer instruction.
2. Arithmetic instruction.
3. Logical Instruction.
4. Boolean variable manipulation instruction.
5. Program branching instructions.
ANSWER Q12. For the given set of instruction name the operation and addressing modes.
i) MOV A,#n
ii) MOV A, addr
iii) MOVX A,@DPTR
iv) MOVC A,@A+DPTR
v) XCH A,Rn
Ans: i) Opeartion: Copy the immediate 8 bit data into the accumulator.
Addressing mode: Immediate add mode.
It is a 2 byte instruction.
ii) Opeartion: Copy the contents of the internal RAM address (addr) into the accumulator.
Addressing mode: Direct addressing mode.
It is a 2 byte instruction.
iii) Opeartion: Copy the contents of the external RAM address stored in DPTR into the accumulator.
Addressing mode: Indirect addressing mode.
It is a 1 byte instruction.
iv) Operation: Copy the code byte, found at the ROM address formed by adding A and the DPTR, into the accumulator.
It is a 1 byte instruction.
v) Operation: Exchange data bytes between the accumulator and the register Rn.
Addressing: Register Addressing mode.
It is a 1 byte instruction.
ANSWER Q13. What are the various jump instructions in microcontroller?
Ans: It is of two types- conditional jump and unconditional jump. Conditional jump is of two types byte level instruction an bit level instruction. Similarly unconditional jump is also divided into 3 sub-jump and these are- Short jump, Absolute jump, Long jump.
ANSWER Q14. What do you mean by subroutine?
Ans: A subroutine is a program that may be used many times in the execution of a larger program.
ANSWER
Note: For more questions on Microcontroller go through your books. And analyze your lab programs well cause maximum questions will be asked from there only.
AC SET-3 Q1. What are flip flops ?
Ans: It is an electronic circuit (a bistable multivibrator) that has two stable states and thereby is capable of serving as one bit of memory.
ANSWER Q2. What is a multivibrator ?
Ans: A multivibrator is an electronic circuit used to implement a variety of sample two state systems such as oscillators, timers and flip-flops. It is characterized by two amplifying devices (transistors, electron tubes or other devices) cross coupled by resistors and capacitors. The most common form is the stable or oscillating type, which generates a square wave- the high level of harmonics in its output is what gives the multivibrator its common name.
ANSWER Q3. What is the purpose of multivibrator ?
Ans: The multivibrator is one form of relaxation oscillator, the frequency of which may be controlled by external synchronizing pulses.
ANSWER Q4. What is an astable multivibrator called so ?
Ans: There is no stable state where the circuit can come to rest, so this circuit is known as an astable multivibrator.
ANSWER Q5. Why is an monostable multivibrator called so ?
Ans: The monostable circuit has only one stable state (output low) hence the name monostable.
ANSWER Q6. What is an astable multivibrator ?
Ans: Astable multivibrator is a two stage switching circuit in which the output of the first stage is fed to the input of the first stage and vice versa. The output of both the stages are complementry. It has two stable states and switches back and forth from one state to another, remaining in state for a time depending upon the discharging of the capacitive circuit.
ANSWER Q7. What is a monostable multivibrator ?
Ans: Monostable multivibrator often called a one shot multivibrator is a pulse generating circuit in which the duration of this pulse is determined by the RC network connected externally to the 555 timer.
ANSWER Q8. What is the purpose of monostable multivibrator ?
Ans: A monostable device, on the other hand, is only able to hold in one particular state indefinitely. Its other state can only be held momentarily when triggered by an external input.
ANSWER Q9. Give some examples of multivibrator.
Ans: The flip-flop is a free running multivibrator.
ANSWER Q10. Mention the applications of multivibrator.
Ans: It finds applications in a variety of systems where square waves or timed intervals are required. Simple circuits tend to be inaccurate since many factors affect their timing, so they are rarely used where very high precision is required.
ANSWER Q11. What is the principle of monostable multivibrator ?
Ans: All monostable multivibrators are timed devices. That is, their unstable output state will hold only for a certain minimum amount of time before returning ti its stable state.
ANSWER Q12. How does a monostable multivibrator work in terms of the astable multivibrator ?
Ans: Like the astable multivibrator, one transistor conducts and the others cut-off when the circuit is energized.
ANSWER Q13. What is the disadvantage of an astable multivibrator ?
Ans: When the astable m/v was first energized, it was impossible to predict which transistor would initially go to cut-off because of circuit symmetry.
ANSWER Q14. What are the different types of multivibrator circuits?
Ans: There are three types of m/v circuits: Astable, Monostable, Bistable.
ANSWER Q15. What is Schmitt trigger ?
Ans: The schmitt trigger is a comparator application which switches the output negative when the input passes upward through a positive reference voltage. It then uses negative feedback to prevent switching back to the other state until the input passes through a lower threshold voltage, thus stabilizing the switching against rapid triggering by noise as it passes the trigger point. In electronics, a schmitt trigger is a comparator circuit that incorporates positive feedback.
ANALOG COMMUNICATION VIVA QUESTIONS WITH ANSWER SET-2
Q1. What is PAM?
Ans: Pulse amplitude modulation, acronym PAM, is a form of signal modulation where the amplitude of a carrier consisting of a periodic train of rectangular pulses is varied in proportion to the sample values of a message signal. In this type of modulation, the pulse duration is held constant.
ANSWER Q2. What are the drawbacks of PAM?
Ans: Before sampling a signal, it must be passed through a low-pass filter, so that the higher frequencies are eliminated from the signal and the signal conforms to the requirement of the sampling circuit. Also, the PAM technique has the same signal to noise ratio as the AM. Thus, it is not employed in the practical circuits but may be employed to produce other forms of pulse modulation.
Q3. How is demodulation done in PAM?
Ans: Demodulation is performed by detecting the amplitude level of the carrier at every period.
ANSWER Q4. Mention the application of PAM.
Ans: PAM is widely used in baseband transmission of digital data, with non baseband application having been largely superseded by pulse-code modulation and more recently by PPM.
ANSWER Q5. What is PAM in practical circuits ?
Ans: PAM is “pulse shaping”. Essentially, communications engineer realize that the shape of the pulse in the time domain can positively or negatively affect the characteristics of that pulse in frequency domain.
ANSWER Q6. What is the basic principle of PAM ?
Ans: In PAM, the amplitude of individual pulses in the pulse train is varied from its default value in accordance with the instantaneous amplitude of the modulating signal at sampling intervals. The width of the pulse is kept constant.
ANSWER Q7. What are the advantages of PAM ?
Ans: Main advantages of PAM are simple transmitter and receiver design. PAM is used to carry information as well as to generate other pulse modulations.
ANSWER Q8. What is a filter ?
Ans: A filter is a device that passes electric signal at certain frequencies of frequency range while preventing the passage of others.
ANSWER Q9. What are the different types of filters ?
Ans: Low-pass, high-pass, Band-pass, Band-elimination ( also referred to as band reject or notch).
ANSWER Q10. What are active filters ?
Ans: Active filters are the circuits that use an operational-amplifier as the active device in combination with some resistors and capacitors to provide an LRC-like filters performance at low frequencies.
ANSWER Q11. What is a low-pass filter ?
Ans: a low pass filter is a filter that passes low frequency signal but attenuates signal with frequencies higher than the cut-off frequency.
ANSWER Q12. Why inductors are not often used in active filters ?
Ans: Inductors are bulky and costly and may have large internal resistive components.
ANSWER Q13. What is an ideal low pass filter ?
Ans: An ideal low pass filter is a network which passes all the frequency up to cut-off frequency fc, and blocks all frequencies above fc.
ANSWER Q14. What is difference between an ideal and a practical low pass filter ?
Ans: The transition region present in practical filters doesn’t exist in an ideal filter. An ideal low-pass filter can be realized mathematically by multiplying a signal by the rectangular function in the frequency domain or, equivalently, Convolution with a sinc function in the time domain.
ANSWER Q15. What is high-pass filter ?
Ans: a high pass filter is a circuit that attenuates all signals below a specified cut-off frequency.
ANSWER Q16. What does the term “pass” mean in any low-or-high pass filters ?
Ans: Pass: to cause or permit to go past or through a barrier.
ANSWER Q17. What does “roll-off” mean ?
Ans: It means that if you set the cut-off frequency for say 450Hz, any signal coming through to the input of the filter is 96dB down at 900 Hz. Set it for 1KHz, signals at 2KHz are down 96dB.
ANSWER Q18. What are passive filters ?
Ans: Passive filters are implemented using only passive components such as resistors, capacitors and inductors. These filters do not produce any amplification of the input signal.
ANSWER Q19. What is a pass band ?
Ans: The range of frequencies that is transmitted.
ANSWER Q20. What is drop band ?
Ans: The range of frequencies that is attenuated.
ANSWER Q21. Why is butterworth filter used most often ?
Ans: in many low pass filter applications, it is necessary for the closed loop gain to be as close to 1 as possible within the baseband. Butterworth filter is best suited for this type of application.
ANSWER Q22. What is Band pass filter ?
Ans: It passes a band of frequencies and attenuates frequencies on both sides of the pass band. You make take an example of series resonant circuit for the explanation.
ANSWER Q23. What is sn idesl band pass filter ?
Ans: The ideal band pass filter can be used to isolate the component of a time series that lies within a particular band of frequencies.
ANSWER Q24. What are band reject circuits ?
Ans: Band reject filters are tuned circuits that prevent the passage of signal within a specified band of frequencies. These devices are also known as band stop or notch filters.
ANSWER Q25. Name the types of band rejection filters.
Ans: Twin-T & active Wein-Robinson circuit.
ANSWER Q26. What are signal filters ?
Ans: Signal filters block or decrease unwanted frequencies or signal wave characteristics.
ANSWER Q27. What are digital filters ?
Ans: Digital filters use digital signal processing (DSP) to perform numerical calculations on sampled values of a signal.
ANSWER Q28. What is precision rectifier ?
Ans: It is an op-amp voltage follower, with a diode inserted between the op-amp output terminals and the circuit output point.
ANSWER Q29. Why use an op-amp as a rectifier ?
Ans: In diode rectifiers circuit, the voltage drop that occurs with an ordinary semiconductor rectifier can be eliminated to give precision rectification.
ANSWER Q30. What is a precision full wave rectifier ?
Ans: a full wave precision rectifier consists of a summing circuit and a precision half wave rectifier which has a voltage gain of 2.
ANSWER Q31. What are the advantages of precision amplifier ?
Ans: Gain of upto 100 can be achieved in this configuration, which is useful for signal conditioning of low output of transducers in mV range.
ANSWER Q32. What is DAC ?
Ans: The process of conversion of digital signal to analog signal is called so.
ANSWER Q33. What are the different types of DAC technique?
Ans: 1) R-2R DAC 2) Binary weighted DAC.
ANSWER Q34. What is an R-2R ladder network?
Ans: A 4-bit R-2R ladder network consists of digitally controlled switches, current to voltage converter and a resistance network.
Note: For more detail about R-2R ladder, go through your book.
ANSWER Q35. What is an oscillator?
Ans: An oscillator is a semiconductor device consisting of a semiconductor specimen placed in magnetic field, and a resistor after a power supply.
ANALOG COMMUNICATION VIVA QUESTIONS WITH ANSWER SET-1
Q1. What is amplitude modulation?
Ans: The process of amplitude modulation consists of varying the peak amplitude of a sinusoidal carrier wave in proportion to the instantaneous amplitude of the modulation signal.
ANSWER Q2. What is modulation?
Ans: Modulation may be defined as the process by which some parameters of a high frequency signal termed as carrier, is varie in accordance with the signal to be transmitted.
Q3. What are the different types of analog modulation?
Ans: 1) Amplitude modulation 2) angle modulation.
ANSWER Q4. What si the need for modulation?
Ans: Consider, for example, picture signal of a T.V camera. It has frequency spectra of DC to 5.5MHz.such a wide band of frequency can’t be propagated through ionosphere. However, if this signal is modulated with a carrier in VHF and UHF range, the percentage bandwidth becomes very small and the signal become suitable for transmission through atmosphere.
ANSWER Q5. What are the objectives met by modulation?
Ans: Length of antenna is shortened, signal loss is reduced, ease of radiation, adjustment of bandwidth, shifting signal frequency of the assigned value.
ANSWER Q6. What are the advantage of PAM and PWM?
Ans: PWM system gives a greater signal to noise ratio as compared to PAM but requires a larger bandwidth to achieve this.
ANSWER Q7. What is Pulse position modulation?
Ans: Pulse position modulation (PPM) is the process in which the position of a standard pulse is varied as a function of the amplitude of the sampled signal.
ANSWER Q8. What is the advantage of PPM over PWM and PAM?
Ans: The phase deviation are usually small. The noise produces a smaller disturbing effect on the time position of the modulating pulse train and as a result, PPM waves have a better performance with respect to signal to noise ratio in comparison to PAM and PWM systems.
ANSWER Q9. What are the applications of pulse position modulation?
Ans: It is primarily useful for optical communication systems, where there tends to be little or no multipath interference. Narrowband RF (Radio frequency) channels with low power and long wavelength (i.e., low frequency) are affected primarily by flat fading, and PPM is better suited.
ANSWER Q10. What is the purpose of using differential pulse position modulation?
Ans: It is possible to limit the propagation of errors to adjacent symbols, so that an error in measuring the differential delay of one pulse will affect only two symbols, instead of effecting all successive measurements.
ANSWER Q11. What are the advantage of PPM?
Ans: One of the principle advantages of pulse position modulation is that it is an M-ary modulation technique that can be implemented non-coherently, such that the receiver does not need to use a phase-locked loop (PLL) to track the phase of the carrier. This makes it a suitable candidate for optical communications systems, where coherent phase modulation and detecting are difficult and extremely expensive. The only other common M-ary non-coherent modulation technique is M-ary frequency shift keying, which is the frequency domain dual to PPM.
The other advantages of pulse position modulation are:
• The amplitude is held constant thus less noise interference.
• Signal and noise separation is very easy.
• Due to constant pulse widths and amplitudes, transmission power for each pulse is same.
ANSWER Q12. What are the application of PPM?
Ans: PPM is employed in narrowband RF channel systems, with the position of each pulse representing the angular position of an analogue control on the transmitter, or possible states of binary switch. The number of pulse per frame gives the number of controllable channels available. The advantage of using PPM for this type of application is that the electronics required to decode the signal are extremely simple, which leads to small, light-weight receiver/decoder units. (Model aircraft require parts that are as lightweight as possible).
ANSWER Q13. Explain the principle of PPM?
Ans: The amplitude and the width of the pulse is kept constant in this system, while the position of each pulse, in relation to the position of a recurrent reference pulse is varied by each instantaneous sampled value of the modulating wave. This means that the transmitter must send synchronizing pulses to operate timing circuits in the receiver. The PPM has the advantage of requiring constant transmitter power output, but the disadvantage of depending on transmitter-receiver synchronization.
ANSWER Q14. What is the puprpose of PPM?
Ans: PPM may be used to transmit analog information, such as continuous speech or data.
ANSWER Q15. What are the analog analogies of PAM, PPM & PWM?
Ans: PAM is similar to AM; PPM and PWM is similar to angle modulation.
ANSWER Q16. What is Frequency modulation (FM)?
Ans: Frequency modulation is the process of varying the frequency of a carrier wave in proportion to the instantaneous amplitude of the modulating signal without any variation in the amplitude of the carrier wave.
ANSWER Q17. What is PWM or Pulse length modulation or pilse duration modulation?
Ans: In PWM, the pulse amplitude is kept constant but the leading edge, trailing edge or both may be varied as a function of the amplitude of the sampled signal and care must be taken to ensure that the pulse don’t overlap in a TDM system.
ANSWER Q18. What are the disadvantages of PWM?
Ans: PWM, in general, requires a greater average power than PAM systems. Also, the PWM system requires a greater bandwidth than PAM.
ANSWER Q19. Explain the principle of PWM?
Ans: Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to either convey information over a communication channel or control the amount of power sent to a load. PWM uses a square wave whose pulse width is modulated resulting in the variation of the average value of the waveform is directly dependent on the duty cycle D.
ANSWER Q20. Mention the applications of PWM.
Ans: PWM can be used to reduce the total amount of power delivered to a load without losses normally incurred when a power source is limited by resistive means. This is because the average power delivered is proportional to the modulation duty cycle. With a sufficiently high modulation rate, passive electronic filters can be used to smooth the pulse train and recover an average analog waveform.
How many types of diffraction are there? Which they are?
Distinguish between Fresnel and Fraun hofer classes of diffraction.
Distinguish between interference and diffraction.
What is grating? Define grating constant.
How do you distinguish between diffraction and refraction?
What is semiconductor?
What is zener diode?
On what factor does the breakdown voltage of zener diode depends?
What is breakdown voltage? Explain.
What is the difference between ordinary diode and zener diode?
Mention some uses of Zener diode.
What do you mean by forward and reverse biasing?
What are the applications of Semi conductor diode?
Explain the types of breakdown.
What do you mean by resonance?
What do you mean by sharpness of resonance?
What is the condition of resonance?
Define quality factor ‘Q’ of a series circuit.
What is the importance of series resonant circuit?
What is resonance? Why current is maximum in series resonance and minimum in parallel resonance?
What is mean by band width?
What is the physical significance of Q-factor?
What is the value of plank constant?
What the factors on which the value of plank’s constant depend?
What is Quantum theory of light?
What is LED?
What do you mean by turn on voltage?
Is the supply voltage and turn on voltage are same?
What is threshold frequency?
What are the applications of LED?
Explain the difference between LASER and LED.
What is the transistor? Why it is called so?
How many types of transistors are there?
How do you identify the terminals in a transistor?
What are the differences between PNP and NPN transistor?
What are active device and passive device?
What do you mean by active biasing?
What is doping?
Mention some of the applications of transistor?
What is perfect black body?
Explain the distribution of energy in a black body spectrum.
Name the various laws of black body radiation.
State Stefan’s law.
What is the value of Stefan’s constant?
Define electric power.
Define emissive power and absorptive power.
Which are the sources of radiation?
What is the difference between intrinsic and extrinsic semiconductor?
Define an electron volt (ev).
What is energy gap? What is its value for Ge and Si?
What is the difference between conductor and insulator based on energy band structure?
What are free electrons?
What are valance band and conduction band?
What is dielectric material? Give example.
What is dielectric loss?
What is a capacitor?
How capacitance of a capacitor can be increased?
What is the difference between dielectric and insulator?
What is a unit of capacitance?
Give applications of dielectric.
Define Fermi level, Fermi energy, Fermi factor, drift velocity, mean free path, collision time, relaxation time, mobility, Fermi temperature.
What are conductors?
What is effect of temperature on electrical conductors?
What is electrical resistivity?
Why the resistivity increase with temperature for metals? Explain.
What are the advantages of four probe technique?
Why the resistivity of semiconductors decreases with increase in temperature?
What do you mean by Ultrasonic waves?
Define sonic, infrastructure and hypersonics.
What is transducer?
What do you mean by cosmic rays?
What is diffraction of light?
What is piezo-electric effect?
Mention some applications of piezoelectric crystals.
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