Category: ECE VIVA Questions

Analog Communication VIVA Questions :-

Analog Communication is a data transmitting technique in which information signal is transmitted in analog nature. This always utilizes continuous signals to transmit data which may obtained from audio, image, video etc. An Analog signal is a variable signal continuous in both time and amplitude. To produce modulated signal inside the transmitter in Analog Communication, analog signal modulates the high carrier frequency. Than this modulated signal is transmitted with the help of antenna. All AM, FM audio transmission and T.V. transmission are the most preferable examples of analog communication. Analog communication is very important topic for the students preparing for GATE Exam(Electronics) Following questions will help to learn the basics concepts of analog communication.

1. Define Pam And Write Down Its Drawbacks?

Pulse Amplitude Modulation is the process by which the amplitude of the regularly spaced pulses varies according to the the amplitude of the modulating signal.

The drawbacks are:

• Since the amplitude of the pulses varies therefore the peak power of the modulating s/g is much greater.
• The bandwidth required for transmitting is greater since the amplitude varies.

2. How Can Be Aliasing Be Avoided?

Aliasing can be avoided if:

1. Sampling frequency must be greater than the frequency of the modulating signal.
2. The frequency should be band limited to maximum frequency of the signal(fm) Htz.
3. If prealias filter is used.

3. State The Advantages Of Super Heterodyning?

The advantages are:

• High selectivity and sensitivity.
• No change in Bandwidth that is bandwidth remains same all over the operating range.
• High adjacent channel rejection.

4. What Do You Mean By Fm And Classify Fm?

Frequency Modulation can be defined as the frequency of the carrier (wc) is varied acc. to the modulating signal about an unmodulated frequency.

FM are of 2 types:

1. Narrowband FM
2. Wideband FM

5. What Do You Mean By Nyquist Rate?

In case of Nyquist rate, the sampling frequency is equal to the maximum frequency of the signal and therefore the successive cycles of the spectrum does not overlap.

6. What Is Amplitude Modulation?

Amplitude Modulation is defined as the process in which the instantaneous value of the amplitude of the carrier is varied according to the amplitude of the modulating or base band signal.

7. What Is Modulation? What Happens In Over Modulation?

Modulation is defined as the process in which some characteristics of the signal called carrier is varied according to the modulating or baseband signal. For example – Amplitude Modulation, Phase Modulation, Frequency Modulation.

In case of over modulation, the modulation index is greater than one and envelope distortion occurs.

8. What Is Multiplexing? Name The Types Of Multiplexing?

Multiplexing is defined as the process in which a number of message signals are combined together to form composite signals so that they can be transmitted through the common channel.

The two types of multiplexing are:

• Frequency Division Multiplexing: In this technique, fixed frequency bands are allotted to every user in the complete channel bandwidth. Such frequency is allotted to user on a continuous basis.
• Time Division Multiplexing: When the pulse is present for the short time duration and most of the time their is no signal present inbetween them than this free space between the two pulses can occupied by the pulses from other channels. This is known as Time Division Multiplexing.

9. What Is Sampling? What Is Sampling Theorem?

Sampling is defined as the process in which an analog signals are converted into digital signals. It means that a continuous time signal is converted into a discrete time signal.

Sampling Theorem is defined as : ’The continuous time signal that can be represented in its samples and recovered back if the sampling frequency (fs) is greater than the maximum frequency of the signal (fm) that is fs >2fm’.

10. What Is Under Sampling?

Under sampling is also known as aliasing effect in which the the sampling frequency is less than the maximum frequency of the signal and therefore the successive cycles of the spectrum overlap.

11. 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.

12. What is modulation?

Ans: Modulation may be defined as the process by which some parameters of a high freuency signal termed as carrier, is varie in accordance with the signal to be transmitted.

13. What are the different types of analog modulation?

Ans:

1. Amplitude modulation
2. angle modulation.

14. What si the need for modulation?

Ans: Consider, for example, picture signal of a T.V camera. It has freuency spectra of DC to 5.5MHz.such a wide band of freuency 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.

15. 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 freuency of the assigned value.

16. What are the advantage of PAM and PWM?

Ans: PWM system gives a greater signal to noise ratio as compared to PAM but reuires a larger bandwidth to achieve this.

17. 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.

18. 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.

19. 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 freuency) channels with low power and long wavelength (i.e., low freuency) are affected primarily by flat fading, and PPM is better suited.

20. 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.

21. What are the advantage of PPM?

Ans: One of the principle advantages of pulse position modulation is that it is an M-ary modulation techniue 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 techniue is M-ary freuency shift keying, which is the freuency 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.

22. 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 reuired to decode the signal are extremely simple, which leads to small, light-weight receiver/decoder units. (Model aircraft reuire parts that are as lightweight as possible).

23. 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 reuiring constant transmitter power output, but the disadvantage of depending on transmitter-receiver synchronization.

24. What is the puprpose of PPM?

Ans: PPM may be used to transmit analog information, such as continuous speech or data.

25. What are the analog analogies of PAM, PPM & PWM?

Ans: PAM is similar to AM; PPM and PWM is similar to angle modulation.

26. What is Freuency modulation (FM)?

Ans: Freuency modulation is the process of varying the freuency of a carrier wave in proportion to the instantaneous amplitude of the modulating signal without any variation in the amplitude of the carrier wave.

27. 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.

28. What are the disadvantages of PWM?

Ans: PWM, in general, reuires a greater average power than PAM systems. Also, the PWM system reuires a greater bandwidth than PAM.

29. 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 suare 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.

30. 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.

ANALOG Communication VIVA Questions and Answers

VLSI viva Questions :-

1. Why does the present VLSI circuits use MOSFETs instead of BJTs?

Compared to BJTs, MOSFETs can be made very small as they occupy very small silicon area on IC chip and are relatively simple in terms of manufacturing. Moreover digital and memory ICs can be implemented with circuits that use only MOSFETs i.e. no resistors, diodes, etc.

2. What are the various regions of operation of MOSFET? How are those regions used?

MOSFET has three regions of operation: the cut-off region, the triode region, and the saturation region.
The cut-off region and the triode region are used to operate as switch. The saturation region is used to operate as amplifier.

3. What is threshold voltage?

The value of voltage between Gate and Source i.e. VGS at which a sufficient number of mobile electrons accumulate in the channel region to form a conducting channel is called threshold voltage (Vt is positive for NMOS and negative for PMOS).

4. What does it mean “the channel is pinched off”?

For a MOSFET when VGS is greater than Vt, a channel is induced. As we increase VDS current starts flowing from Drain to Source (triode region). When we further increase VDS, till the voltage between gate and channel at the drain end to become Vt, i.e. VGS – VDS = Vt, the channel depth at Drain end decreases almost to zero, and the channel is said to be pinched off. This is where a MOSFET enters saturation region.

5. Explain the three regions of operation of a MOSFET.

Cut-off region: When VGS < Vt, no channel is induced and the MOSFET will be in cut-off region. No current flows. Triode region: When VGS ≥ Vt, a channel will be induced and current starts flowing if VDS > 0. MOSFET will be in triode region as long as VDS < VGS – Vt.
Saturation region: When VGS ≥ Vt, and VDS ≥ VGS – Vt, the channel will be in saturation mode, where the current value saturates. There will be little or no effect on MOSFET when VDS is further increased.

6. What is channel-length modulation?

In practice, when VDS is further increased beyond saturation point, it does has some effect on the characteristics of the MOSFET. When VDS is increased the channel pinch-off point starts moving away from the Drain and towards the Source. Due to which the effective channel length decreases, and this phenomenon is called as Channel Length Modulation.

7. Explain depletion region.

When a positive voltage is applied across Gate, it causes the free holes (positive charge) to be repelled from the region of substrate under the Gate (the channel region). When these holes are pushed down the substrate they leave behind a carrier-depletion region.

8. What is body effect?

Usually, in an integrated circuit there will be several MOSFETs and in order to maintain cut-off condition for all MOSFETs the body substrate is connected to the most negative power supply (in case of PMOS most positive power supply). Which causes a reverse bias voltage between source and body that effects the transistor operation, by widening the depletion region. The widened depletion region will result in the reduction of channel depth. To restore the channel depth to its normal depth the VGS has to be increased. This is effectively seen as change in the threshold voltage – Vt. This effect, which is caused by applying some voltage to body is known as body effect.

9. Give various factors on which threshold voltage depends.

As discussed in the above question, the Vt depends on the voltage connected to the Body terminal. It also depends on the temperature, the magnitude of Vt decreases by about 2mV for every 1oC rise in temperature.

10. Give the Cross-sectional diagram of the CMOS.

VLSI VIVA Questions and Answers :

11) Mention what are three regions of operation of MOSFET and how are they used?

12) Explain what is the depletion region?

13) Explain why is the number of gate inputs to CMOS gates usually limited to four?

14) Explain what is multiplexer?

15) Explain what is SCR (Silicon Controlled Rectifier)?

16) Explain what is Slack?

17) Explain what is the use of defpararm?

18) Explain how logical gates are controlled by Boolean logic?

19) Mention what are the different gates where Boolean logic are applicable?

20) Explain how binary number can give a signal or convert into a digital signal?

SATELLITE Communication Viva Questions :-

1 What are the Types of Satellite?

Types of Satellite are as under:

1. Anti-Satellite weapons/”Killer Satellites”
2. Astronomical satellites
3. Bio-satellites
4. Communications satellites
5. Miniaturized satellites
6. Navigational satellites
7. Reconnaissance satellites
8. Earth observation satellites
9. Space stations
10. Tether satellites
11. Weather satellites

2 How do I interpret visible satellite pictures?

The pictures sent back to us from Weather Satellites are simply photographs taken from outer space. We get visible images during the daylight when the earth reflects sunlight back to outer space. Visible pictures show the amount of light reflected back to outer space. Thick water rich clouds, such as stratus (common along the North Coast during Summer months), show up as bright white on visible pictures. Snow pack over the Sierra Nevada during the Winter is another good reflector of sunlight. During the night, visible pictures are completely black as there is very little or no visible light to reflect!

3 How do I interpret infrared satellite pictures?

Clouds and atmospheric gases such as water vapor radiate infrared energy to space. The amount of energy radiated by clouds and gasses relates directly with its temperature. This relationship, know as the Stephan-Boltzmann Law, allows us to “see” clouds at night. The atmosphere generally cools with height. A cloud that radiates low energy is higher in the troposphere than a cloud that radiates higher energy. On a standard linear enhancement curve, bright white represent cold ice-crystal clouds, while clouds colored with light shades of gray are warm water filled clouds in the mid and lower troposphere. There are a number of enhancement curves that color pictures of clouds based on temperature. These curves accentuate temperature ranges that allow us to discern high clouds from mid and low clouds. At the bottom of every infrared image there is a key telling you the temperature range for that color. For example, on the infrared pictures provided on this web site, red represents cloud tops with a temperature of -40C which in a standard atmosphere is about 40,000 ft.

4 How do I interpret water vapor imagery?

Water vapor in the mid and upper troposphere absorbs infrared energy at discrete wavelengths. Using this information, water vapor can act like a tracer of atmospheric circulation in the mid and upper troposphere. Dark regions on water vapor pictures are generally areas where the air is sinking and drying. Light colored regions are areas of rising motion and moisture. Water vapor images are useful in locating jet streams and short-wave troughs and ridges in the mid and upper troposphere, but are lousy when trying to see clouds near the ground such as stratus.

5 Where can I find the time on satellite pictures? What time zone is this?

The date and time stamps are located at the top or bottom of every image, along with other information. For example, G-10 IMG 01 3 Jun 00 TIME=00:30UTC RES=4km NWS/WR=SSD, is a typical date-time stamp which appears on satellite images. The date and time, colored blue in the above example, is in Universal Coordinated Time (UTC). UTC is also known as Greenwich Mean Time (GMT) or Zulu Time (Z). Along the West Coast, we are about 8 hours behind the UTC during Pacific Standard Time (PST). During Daylight Saving Time (PDT), from mid April through mid October, we are about7 hours behind the UTC. In the example above, it’s June 3rd 2000, 30 minutes past midnight in Greenwich England. In order to get local time, you subtract7 hours to get June 2nd 2000, 5:30PM PDT. The next calendar day has already started in Greenwich England!

6 What is Anti-satellite weapon?

Anti-satellite weapons (ASAT) are space weapons designed to incapacitate or destroy satellites for strategic military purposes. Currently, only the United States, the former USSR (now Russia) and the People’s Republic of China are known to have developed these weapons. On September 13, 1985, the United States destroyed US satellite P78-1 using an ASM-135 ASAT anti-satellite missile and malfunctioning US spy satellite USA-193 using a RIM-161 Standard Missile 3 on February 21, 2008. On January 11, 2007, China destroyed an old Chinese orbiting weather satellite.

7. What is Space observatory?

A space observatory is any instrument in outer space which is used for observation of distant planets, galaxies, and other outer space objects. This category is distinct from other observatories located in space that are pointed toward the earth for the purpose of reconnaissance and other types of information gathering.

8. What is Bio satellite?

A bio satellite is a satellite designed to carry life in space.
NASA launched three satellites specifically named Bio satellite (1, 2 & 3) between 1966 and 1969.
Biosatellites include:

• Bion series of satellites
• the Mars Gravity Biosatellite.
• Orbiting Frog Otolith

9. What is Communications satellite?

A communications satellite (sometimes abbreviated to COMSAT) is an artificial satellite stationed in space for the purpose of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, Molniya orbits, other elliptical orbits and low (polar and non-polar) Earth orbits.

10. What is Miniaturized satellite?

Miniaturized satellites or small satellites are artificial satellites of unusually low weights and small sizes, usually under 500 kg (1100 lb). While all such satellites can be referred to as small satellites, different classifications are used to categorize them based on mass.

11. What is Global navigation satellite system?

Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite navigation systems (“sat nav”) that provide autonomous geo-spatial positioning with global coverage. GNSS allows small electronic receivers to determine their location (longitude, latitude, and altitude) to within a few metres using time signals transmitted along a line-of-sight by radio from satellites. Receivers calculate the precise time as well as position, which can be used as a reference for scientific experiments.

12. What is Spy satellite?

A spy satellite officially referred to as a reconnaissance satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications.
These are essentially space telescopes that are pointed toward the Earth instead of toward the stars. The first generation type took photographs, then ejected canisters of photographic film, which would descend to earth.

13. What is Earth observation satellite?

Earth observation satellites are satellites specifically designed to observe Earth from orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. Geostationary satellites hover over the same spot, providing continuous monitoring to a portion of the Earth’s surface. Polar orbiting satellites provide global coverage, but only twice per day at any given spot.

14. What is Space station?

A space station is an artificial structure designed for humans to live and work in outer space for a period of time.
To date, only low earth orbital (LEO) stations have been implemented, otherwise known as orbital stations. A space station is distinguished from other manned spacecraft by its lack of major propulsion or landing facilities—instead, other vehicles are used as transport to and from the station. Current and recent-history space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years. The only space station currently in use is the International Space Station. Previous stations include the Almaz and Salyut series, Skylab and Mir.

15. What is Tether satellite?

Tether satellite is a satellite connected to another by a thin cable called a tether. The space tether idea had its origin in the late 1800s. The idea became more popular in the 1960s, and subsequently NASA examined the feasibility of the idea and gave direction to the study of tethered systems, especially tethered satellites.

16. Explain Weather satellite?

Weather Satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while moving at the speed of the Earths rotation. These meteorological satellites, however, see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., are other types of environmental information collected using weather satellites.

EDC LAB VIVA Questions :-

1. What is Electronic?
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.

2. What is communication?
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver. (or)communication says as transferring of message from one place to another place called communication.

3. Different types of communications? Explain.
Analog and digital communication.
As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of “1”s and “0”s.
Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.

4. What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

5. State sampling theorem?
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.

6. What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.

7. What is pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

8. What is stop band?
A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

9. Explain RF?
Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

10. What is modulation? And where it is utilized?

Modulation is the process of varying some characteristic of a periodic wave with an external signals.
Radio communication superimposes this information bearing signal onto a carrier signal.
These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal.
Modulation is utilized to send an information bearing signal over long distances.

11. What is demodulation?
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.

12. Name the modulation techniques?
For Analog modulation–AM, SSB, FM, PM and SM
Digital modulation–OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

13. Explain AM and FM?
AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal.
FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.

14. Where do we use AM and FM?
AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.

15. What is a base station?
Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.

16. How many satellites are required to cover the earth?
3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.

17. What is a repeater?
A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.

18. What is an Amplifier?
An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.

19. Example for negative feedback and positive feedback?
Example for –ve feedback is —Amplifiers And for +ve feedback is – Oscillators.

20. What is Oscillator?
An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.

21. What is an Integrated Circuit?
An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their main advantages are low cost, low power, high performance, and very small size.

22. What is crosstalk?
Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions, networking equipment, and even electric guitars.

23. What is resistor?
A resistor is a two-terminal electronic component that opposes an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm’s law:
V = IR.

25. What is inductor?
An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.

26. What is conductor?
A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.

27. What is a semi conductor?
A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator(An Insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself); it can vary over that wide range either permanently or dynamically.

28. What is diode?
In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.

29. What is transistor?
In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits.

30. What is op-amp?
An operational amplifier, often called an op-amp , is a DC-coupled high-gain electronic voltage amplifier with differential inputs[1] and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation.

31. What is a feedback?
Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system.

32. Advantages of negative feedback over positive feedback?
Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.

33. What is Barkhausen criteria?
Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations.
“Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the
transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity”.
The condition of unity loop gain -Aβ = 1 is called the Barkhausen criterion. This condition implies that
Aβ= 1and that the phase of – Aβ is zero.

34. What is CDMA, TDMA, FDMA?
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division). In CDMA, they would speak different languages. People speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

35. explain different types of feedback?
Types of feedback:
Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system’s output, inverted, into the system’s input; generally with the result that fluctuations are attenuated.
Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as “cumulative causation”, is a feedback loop system in which the system responds to perturbation (A perturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system.
Bipolar feedback: which can either increase or decrease output.

36. What are the main divisions of power system?
The generating system,transmission system,and distribution system.

37. What is Instrumentation Amplifier (IA) and what are all the advantages?
An instrumentation amplifier is a differential op-amp circuit providing high input impedances with ease of gain adjustment by varying a single resistor.

38. What is meant by impedance diagram?
The equivalent circuit of all the components of the power system are drawn and they are interconnected is called impedance diagram.

39. What is the need for load flow study?
The load flow study of a power system is essential to decide the best operation existing system and for planning the future expansion of the system. It is also essential for designing the power system.

40. What is the need for base values?
The components of power system may operate at different voltage and power levels. It will be convenient for analysis of power system if the voltage, power, current ratings of the components of the power system is expressed with referance to a common value called base value.

41.Why are the coupling capacitors required?
To filter the Dc term from the Input signal , Collector output in amplifiers.

42.What is meant by thermal stabilization?
Maintain a constant operating point when temperature varies

43.Explain why reversal of phase occurs in a BJT CE Amplifier.
As Base voltage increases, base current increases, then collector current increases so voltage drop across Rc increases so out put voltage decreses.

44.What happens if an amplifier is biased at cutoff or at saturation?
In cutoff region Ic is 0, in saturation region Vce is almost Zero.

45.What is the significance of the bandwidth of an amplifier?
Bandwidth specifies the input signal frequency range that can be applied to amplifier to get maximum gain.

46.What is meant by Gain-Bandwidth Product? What is its significance?
The name itself expressing it is the product of gain of a device and its bandwidth. For any system (circuit) gain bandwidth product is constant, if gain increases bandwidth decreases vice versa.

47.What are the advantages of using a FET instead of a BJT?
FET has high input impedance, lower noise, low to medium gain,

48.What are the specifications of the SCR ?
gate trigger voltage, gate trigger current, holding current, on-state voltage, peak gate power dissipation.

49.Can we interchange the source and drain terminals in a FET circuit? Can we do the same with the emitter and collector terminals of a BJT circuit?
We can interchange drain and source but we cannot change emitter and collector because emitter and collectors dimensions and doping concentration is different

50.What is a MOSFET? How is it different from a JFET? What are its typical applications?
Metal oxide semiconductor can be operated in both depletion and enhancement modes, but Junction field effect Transistor can be operated in depletion mode only.

EMBEDDED SYSTEMS LAB VIVA Questions :-

1. What is an embedded system?
An embedded system is a special purpose computer system which is completely encapsulated by device it control. It is a programmed hardware device in which the hardware chip is programmed with specific function. It is a combination of hardware and software.

2. What are the characteristics of embedded system?
The Characteristics of the embedded systems are as follows-

• Sophisticated functionality
• Real time behavior
• Low manufacturing cost
• Low power consumption
• User friendly
• Small size

3. What are the types of embedded system?
They are of 4 types

1. General computing
2. Control System
3. Digital Signal Processing
4. Communication and network

4. What is digital signal controller ?
DSC is 16 bit RISC machine that combines control advantages of micro-controller and digital signal processing to produce tightly coupled single chip-single instruction stream solution for embedded system design.

5. What are the components of embedded system?
Microcontroller, microprocessor, DSC, DSP, busses, system clock, Read only Memory(ROM), RAM, Real time clock these are the components of embedded system.

6. Why we use embedded systems?
Embedded systems avoid lots of electronic components and they have rich built in functionality. They reduces the cost and maintenance cost and the probability of failure of embedded system is less so embedded system are in very much use now a days.

7. What are the languages used in embedded system?
Assembly language and C are basically used for embedded system. Java and ADA are also preferred.

8. How does combination of functions reduce memory reuirement in embedded system?
By using functions the amount of code that has to be dealt with is reduced thus redundancy is eliminated for everything common in function.

9. What is the significance of watchdog timer in ES?
It is a timing device which is set to predefined time interval and some task is to be performed at that time. It is used to reset original state when an inappropriate event take place.It is usually operated by counter device.

10. What is the difference between mutexes and semaphores?
Semaphores are the synchronization tool to overcome critical section problem.
Mutex is also a tool that is used to provide deadlock free mutual exclusion. It protects access to every critical data item, if the data is locked and is in use,it either waits for the thread to finish or awakened to release the lock from its inactive state.

11. What is the difference between FIFO and the memory?
FIFO (first in first out) is a memory structure where data’s can be stored and retrieved. This is a ueue where memory is a storage device which can hold data’s dynamically or at any desired locations and can be retrieved in any order.

12. What is an anti-aliasing filter?
Anti-aliasing filter reduces errors due to aliasing.

13. How to implement a fourth order Butter worth LP filter at 1 KHz if sampling freuency is 8 KHz?
A fourth order butter worth filter can be made as cascade of two second order LP filters with zeta of 0.924 and 0.383. One can use a bilinear transformation approach for realising second order LP filters. Using this techniue described well in many texts, one can make second order LP filters and cascade them

14. Is 8085 an embedded system?
It’s not an embedded system. B’coz it will be a part of an embedded system and it does not work on any software.

15.What is the role of segment register?
In the 8086 processor architecture, memory addresses are specified in two parts called the segment and the offset. Segment values are stored in the segment registers. There are four or more segment registers: Code Segment (CS) contains segment of the current instruction (IP is the offset), Stack segment (SS) contain stack of the segment (SP is the offset), DS is the segment used by default for most data operations; ES is an extra segment register.

16.What type of registers contains an INTEL CPU?
Special function registers like accumulator, program controller (PC), data pointer (DPTR), TMOD and TCON (timing registers), 3 register banks with r0 to r7, Bit addressable registers like B.

17. What is the difference between microprocessor and micro controller?
Microprocessor is managers of the resources (I/O, memory) which lie out-side of its architecture.
Micro controllers have I/O, memory etc. built into it and specifically designed for control.

18. DMA deals with which address (physical/virtual addresses)?
DMA deals with physical addresses. DMA controller is a device which directly drives the data and address bus during data transfer. So it is purely physical address.

19. What is the difference between testing and verification?
Verification is a front end process and testing is a post silicon process. Verification is to verify the functionality of the design during the design cycle. Testing is find manufacturing faults.

EMBEDDED SYSTEMS LAB VIVA Questions and Answers

MPMC LAB VIVA Questions :-

1.What is a Microprocessor?
It is a CPU fabricated on a single chip, program-controlled device, which fetches the instructions from memory, decodes and executes the instructions.

2. Define bit, byte and word.
Bit is either 0 or 1.
Byte is group of 8 bits.
Word is group of 16 bits.

3.What are the different functional units in 8086?
2 units-Bus Interface Unit (BIU) and Execution unit (EU)

4. What is the function of BIU ?
It is used to generate the 20-bit physical address and is responsible for performing all external bus operations.

5. What is the function of EU?
Execution Unit receives program codes and data from BIU, executes these instructions and store the result.

6. What is the maximum size of segment in 8086 microprocessor?
64KB.

7. What is general purpose registers in 8086?
There are 4 general purpose registers are there.

1. AX-ACCUMULATOR
2. BX- BASE
3. CX- COUNT
4. DX-DATA (Extended accumulator)

8. What are the functions of General purpose Registers?

• AX register as 16-bit accumulator, stores all arithmetic and logical operation’s results.
• BX register is used as an offset address Storage.
• CX register is used as counter. Especially used in loop, shift, rotate instructions.
• DX register is used in port operations (IN and OUT)

9. What is special purpose registers in 8086?
CS- CODE SEGMENT
DS-DATA SEGMENT
ES-EXTRA SEGMENT
SS-STACK SEGMENT
BP-BASE POINTER
IP-INSTRUCTION POINTER
SP- STACK POINTER
SI-SOURCE INDEX
DI-DESTINATION INDEX
FLAG REGISTER

10. What are the functions of base Registers?
CS stores program code,
DS stores data
ES sores extra data
SS stores stack data.

11. Name the pin in 8086 microprocessor that is used for selecting mode of operation?
29th pin-MN/MX’
If MN/MX’=0 then maximum mode is selected.
MN/MX’=1 then minimum mode is selected.

12. What is Segment address in 8086?
The part of the segment starting address stored in a segment register is called the segment address.

13. What are the flags in 8086?
In 8086, 9 flags are there. Out of 9, 6 are conditional (status) flags and 3 control flags.
Conditional (status) flags:
Carry flag (CF), Parity flag (PF), Auxiliary carry flag (CF), Zero flag (ZF), Overflow flag (OF), and Sign flag(SF)
Control flags:
Trap flag (TF), Direction flag (DF), Interrupt flag (IF),

14. What is Tri-state logic?
Three Logic Levels are used and they are High (logic 1), Low(logic 0), High impedance(Z) state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions.

15. What is system bus?
Group of address, data and control buses.
Address bus: carry the Address to the memory to fetch either Instruction or Data.
Data bus: carry the Data from the memory.
Control bus: carry the Control signals like RD/WR, reset, ready etc.

16. What is the difference between Maskable interrupts and Non-Maskable interrupts?
An interrupt that can be turned off by the programmer is known as Maskable interrupt.
An interrupt which can be never be turned off (i.e. disabled) is known as Non-Maskable interrupt.

17. What are the different types of Addressing Modes?
There are 12 different types of Addressing Modes. They are:-

1. Immediate:- The Immediate data is a part of instruction.
2. Direct:- A 16-bit memory address (offset) is directly specified in the instruction as a part of it.
3. Register:- Data is stored in a register.
4. Register Indirect:- The address of the memory location which contains data or operand is determined in an indirect way.
5. Indexed:- offset of the operand is stored in one of the index registers.
6. Register Relative:- The data is available at an effective address formed by adding an 8-bit or 16-bit displacement with the content of any one of the registers BX,BP,SI and DI in the default (either DS or ES) segment.
7. Based Indexed:- The effective address of the data is formed, in this addressing mode,by adding content of a base register to the content of an index register.
8. Relative Based Indexed:-  The effective address is formed by adding an 8 or 16-bit displacement with the sum of contents of any one of the base registers and any one of the index registers, in the default segment.
9. Intrasegment Direct Mode:- In this mode, the address to which the control is to bve transferred lies in the segment in which the control transfer instruction lies and appears directly in the instruction as an immediate displacement value.
10. Intrasegment Indirect Mode:- In this mode, the displacement to which the control is to be transferred, is in the same segment in which the control transfer instruction lies, but it is passed to the instruction indirectly.
11. Intersegment Direct:- In this mode, the address to which the control is to be transferred is in a different segment.
12. Intersegment Indirect:- In this mode, the address to which the control is to be transferred lies in a different segment and it is passed to the instruction indirectly sequentially.

18. What is baud rate?
The baud rate is the rate at which the serial data are transmitted. Units- symbols per second.

19. What is a port?
The port is a buffered I/O, which is used to hold the data transmitted from the processor to I/O device or vice-versa.

20. What is 8255?
It is PPI- Programmable Peripheral Interface. it is used to connect I/O devices to microprocessor and supports parallel communication.

21.What are Flag registers?

22.Write the flags of 8086?

23. What are the interrupts of 8086?

24. How clock signal is generated in 8086? What is the maximum internal clock frequency of 8086?

25. Write the special functions carried by the general purpose registers of 8086?

26.What is the need for Port?

27.What is a port?

28.What is processor cycle (Machine cycle)?

29.What is Instruction cycle?

30.What is fetch and execute cycle?

31. In how many ways computer soft wares are categorized?
32. Explain the two types of software?
33. What is an editor?
34. What is an OS and what are its functions?
35. What are the different types of assemblers used?
36. What is a linker?
37. What is a locator?
38. What is coprocessor?
39. What is a coprocessor trap?
40. What is a debugger?
41. In how many groups can the signals of 8085 be classified?
42. What is meant by the statement that 8085 is a 8 bit microprocessor?
43. What is the operating frequency of 8085?
44. What is the purpose of CLK signals of 8085?
45. What are the widths of data bus (DB) and address bus (AB) of 8085?
46. What is the distinguishing feature of DB and AB?
47. The address capability of 8085 is 64 KB.Explain?
48. Does 8085 have serial I/O control?
49. Mention the addressing modes of 8085?
50. What jobs ALU of 8085 can perform?
51. How many hardware interrupts 8085 supports?
52. How many I/O ports can 8085 access?
53. Why the lower byte address bus(A0-A7) and data bus (D0-D7) are multiplexed?
54. List the various registers of 8085?
55. Describe the accumulator register of 8085?
56. What are the temporary registers of 8085?
57. Describe the general purpose registers of 8085?
58. Which are sixteen bit registers of 8085?
59. Discuss PC and SP?
60. Describe the instruction register of 8085?
61. Describe the (status) flag register of 8085?
62. What is the function of ALE and how does it works?
63. Explain the functions of the two DMA signals HOLD and HLDA?
64. Discuss 3 states signals IO/M,S0,S1?
65. What happens when RESET IN(LOW) signal goes low?
66. Function of RESET OUT signal.
67. Indicate different machine cycles of 8085?
68. Name the special purpose registers?
69. Does ALU have any storage facility?
70. Explain XTHL,DAA,RC instructions.
71. What is the difference between JMP and CALL?
72. What happens when CALL instruction is executed?
73. Mention interrupts pins of 8085?
74. Explain maskable and non maskable interrupts?
75. Which is non maskable interrupt for 8085?
76. Do the interrupts of 8085 have priority?
77. What is meant by priority of interrupt?
78. Mention the types of interrupts that 8085 supports?
79. What is the software interrupts of 8085?
80. Explain the software instruction EI and DI?
81. Explain SIM and RIM instructions?
82. What is polling?
83. What is stack?
84. Why stack is used in program?
85. How the stack is initialized?
86. What the SP register does in a program?
87. Comment the size of stack?
88. What type of memory is the stack?
89. What are the software instructions related to stack operations?
90. What are the typical errors associated with using stack in a program?
91. What is a subroutine?
92. Why subroutine used in programs?
93. How subroutine can be called from the main program and how the program returns from the subroutine?
94. Byte wise what are the lengths of CALL and RET instructions?
95. Explain SPHL instruction?
96. Which are the different data transfer schemes?
97. Mention the types of programmed data transfer?
98. Explain DMA?
99. What is meant by address space? what is meant by address space partitioning?
100.Explain memory mapped I/O and I/O mapped I/O schemes?