ECE Interview Questions

ECE Questions and Answers in Interview

                                    1)What is a Microprocessor?

Ans: Microprocessor is a program-controlled device, which fetches the instructions from memory, decodes and executes the instructions. Most Micro Processor are single- chip devices.

2)In 8085 which is called as High order / Low order Register?

Ans: Flag is called as Low order register & Accumulator is called as High order Register.

3)What is Tri-state logic?

Ans: Three Logic Levels are used and they are High, Low, High impedance state. The high and low are normal logic levels & high impedance state is electrical open circuit conditions. Tri-state logic has a third line called enable line.

4)What happens when HLT instruction is executed in processor?

Ans: The Micro Processor enters into Halt-State and the buses are tri-stated.

5)Which Stack is used in 8085?

Ans: LIFO (Last In First Out) stack is used in 8085.In this type of Stack the last stored information can be retrieved first

6)What is Program counter?

Ans: Program counter holds the address of either the first byte of the next instruction to be fetched for execution or the address of the next byte of a multi byte instruction, which has not been completely fetched. In both the cases it gets incremented automatically one by one as the instruction bytes get fetched. Also Program register keeps the address of the next instruction.

7)What are the various registers in 8085?

Ans: Accumulator register, Temporary register, Instruction register, Stack Pointer, Program Counter are the various registers in 8085

8)What is a bus?

Ans: Bus is a group of conducting lines that carries data, address and control signals

9)Why data bus is bi-directional?

Ans: The microprocessor is to fetch (read) the data from memory or input device for processing and after processing it has to store (write) the data to memory or output devices. Hence the data bus is bi-directional.

10)Define T-state?

Ans: T-state is defined as one subdivision of operation performed in one clock period. These subdivisions are internal states synchronized with the system clock, and each T-state is precisely equal to one clock period.

11)What is an instruction cycle?

Ans: The sequence of operations that a processor has to carry out while executing the instruction is called instruction cycle. Each instruction cycle of processor contains a number of machine cycles.

12)What is fetch and execute cycle?

Ans: The instruction cycle is divided in to fetch and execute cycles. The fetch cycle is executed to fetch the opcode from memory. The execute cycle is executed to decode the instruction and to perform the work instructed by the instruction.

13)Convert the octal number 7401 to binary?

Ans: 111100000001

14)What is soft computing?

Ans: The system that learns from present data and experienced data and makes decisions based on knowledge   or Soft computing refers to a collection of computational techniques in a computer science which involve studying, modeling and analyzing complicated phenomenon.

15)What are different learning methods of an artificial intelligence system?

Ans: Rote learning, learning by taking advice, learning by parameter adjustment, learning by analogy

16)What is the importance of membership function in fuzzy logic?

Ans: Membership function is a value that indicates the falsity and the truthness of the fact

17)Applications of AI

Ans: Medical disease diagnosis, robotics and automation, share market for future expectation of market values or share values

18)What is difference between exhaustive search and heuristic search?

Ans: a) Exhaustive search is method of searching a solution without limit and clue.

     b) Heuristic search is an approximation method which assumes some sample values and search for the solution

19)What are the types of motors used in actuators?

Ans: Servo and stepper

20)What is a hydraulic motor?

Ans: A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder.

21)What do you mean by Degree of Freedom (DOF)?

Ans: In mechanics, the degree of freedom (DOF) of a mechanical system is the number of independent parameters that define its configuration. It is the number of parameters that determine the state of a physical system and is important to the analysis of systems of bodies in mechanical engineering, aeronautical engineering, robotics, and structural engineering.

Ex: An automobile with highly stiff suspension can be considered to be a rigid body ravelling on a plane (a flat, two-dimensional space). This body has three independent degrees of freedom consisting of two components of translation and one angle of rotation. Skidding or drifting is a good example of an automobile’s three independent degrees of freedom.

22)What is the difference between robot and intelligent robot?

Ans: a) Robot with simple mechanics     b) Robot with learning and adapting

23)What are the basic stages of image processing to build an application?

Ans: Acquisition, enhancement, segmentation, classification.

24)How an image is formed and digitized?

Ans: Light falls on object and reflects back to sensor which converts to electrical charge and amount of charge decides the amount of intensity. The sampling and quantization plays role in converting the analog electrical charge to digital intensity.

25)What are the applications of image processing in various fields?

Ans: Medical, Surveillance, Satellite, Robotics and automation

26)What are the different formats of images you know and what is the difference?

Ans: JPEG, BMP, PNG, DICOM, TIFF

     Depends on header information

27)What is a System?

Ans :When a number of elements or components are connected in a sequence to perform a specific function, the group of elements that all constitute a System

28)What is Control System?

Ans: In a System the output and inputs are interrelated in such a manner that the output quantity or variable is controlled by input quantity, then such a system is called Control System.
The output quantity is called controlled variable or response and the input quantity is called command signal or excitation.

29)What are different types of Control Systems?

Ans :Two major types of Control Systems are 1) Open loop Control System 2) Closed Loop Control Systems
Open loop Control Systems: The Open loop Control System is one in which the Output Quantity has no effect on the Input Quantity. No feedback is present from the output quantity to the input quantity for correction.
Closed Loop Control System: The Closed loop Control System is one in which the feedback is provided from the Output quantity to the input quantity for the correction so as to maintain the desired output of the system.

30)What is a feedback in Control System?

Ans: The Feedback in Control System in one in which the output is sampled and proportional signal is fed back to the input for automatic correction of the error ( any change in desired output) for further processing to get back the desired output.

31)Why Negative Feedback is preferred in the Control System?

Ans: The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error (deviation from the desired result).
Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

32)What is the effect of positive feedback on stability of the system?

Ans: Positive feedback is not used generally in the control system because it increases the error signal and drives the system to instability. But positive feedbacks are used in minor loop control systems to amplify certain internal signals and parameters.

33)What is a p-n junction diode? State some of its applications.

Ans: A p-n junction is a metallurgical junction formed at the boundary between a p-type and n-type semiconductor created in a single crystal of semiconductor by doping. It acts as a diode as is a two-terminal electronic component with asymmetric transfer characteristics. The following are some of its applications:-

34)What is rectifier? Types of rectifier?

Ans: A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The types of rectifiers are-
i. Half wave rectifier- Uses one p-n junction
ii. Full wave rectifier- Uses two p-n junction

35)What is zener diode?

Ans: Zener diodes: It is very highly doped acts as a voltage regulator and operates under reverse bias in the breakdown region.

Signal diodes & Tunnel diodes

36)Why Negative Feedback is preferred in the Control System?

Answer: The role of Feedback in control system is to take the sampled output back to the input and compare output signal with input signal for error (deviation from the desired result). Negative Feedback results in the better stability of the system and rejects any disturbance signals and is less sensitive to the parameter variations. Hence in control systems negative feedback is considered.

37)What is Time response of the control system?

Answer: Time response of the control system is defined as the output of the closed loop system as a function of time. Time response of the system can be obtained by solving the differential equations governing the system or time response of the system can also be obtained by transfer function of the system.

38)What is Resonant peak?

Answer: Resonant peak is defined as the maximum value of the closed loop transfer function. A large resonant peak corresponds to large overshoot in the transient response

39)What is Phase Margin?

Answer: The phase margin is the amount of additional phase lag at the gain cross over frequency required to bring the system to the verge of instability.

40)What is a PID controller and how can it is applied to our everyday life?

Ans:  PID controller is composed of three components:
P - Proportional
I - Integral
D - Differential
It controls the overall response of a system. The "P" term
controls the gain of the system. The "I" term controls
error and "D" term controls the overshoot of the system. 

41)What is the use of Random Signals?

Ans. Random signals are used to test dynamic response statistically for very small amplitudes and time-duration.

42)What is convolution?

Ans. Convolution is the technique of adding two signals in time domain. We can also do this quite easily by changing the domain of signals from time domain to frequency domain using Fast Fourier Transform (FFT).

43)What is FFT?

Ans. FFT is a fast way to calculate Discrete Fourier Transform (DFT). It is much more efficient then DFT and require less number of coding lines. Due to FFT several kind of techniques are feasible.

44)Why is FFT faster than DFT? What is the actual concept behind this?
Ans: FFT is an algorithm to implement DFT, FFT is not at all a transform,
if u implement Directly it take (N^2) complex Multiplications and (N^2 -N) complex additions , whereas FFT will Nlog2(N) complex Multiplication& additions

45)What is aliasing and how do we prevent it?
Ans: Aliasing is frequency shifting of content of input signal above half the sample frequency. We avoid it by using antialiasing filters to limit signal content below 1/2 sample frequency and/or by sampling at high enough frequency to avoid antialiasing.

46)What is difference between Analog Signal and Digital Signal?

Ans: Analog signal has infinite set of values and Digital Signal has finite sets values.

47)What is difference between Discrete and Digital signal?

Ans: Digital signal has samples at discrete time instants with certain set of values only where as Discrete Signal have samples, which has no limited space of values, it is infinite set of values.

48)What is impulse signal and impulse response?

Ans:Impulse signal is as given in figure has infinite value at t = 0, and 0 else

 

Impulse response of system is response of system when input is impulse signal.

49)What is Fourier Transform and where it is used?

Ans: Fourier Transform covert time domain signal to frequency domain, It tells how many frequencies are available in signal with what strength. It is widely used

1. To analyze signal

2. To Analyze System’s frequency response and many more..

50)What is difference between Fourier Transform and Fourier Series?

Ans: Fourier Transform is computed for Aperiodic continues time signal where as fourier series is computed for Periodic Continues time signal

51)What is different between Fourier Transform and Laplace Transform?

Ans: Laplace Transform is generalization of fourier transform.

52)Why Laplace Transform is widely used than Fourier Transform?

Ans:For Fourier Transform signal should satisfy (sufficiently not necessarily) Dirichlet Criteria, where for computing Laplace Transform it is not required, ROC define that space

53)What is energy signal and Power Signal?

Ans: Energy signal is signal having finite energy, which is time limited, where as power signal is signal whose energy is infinite and power is finite.

54)What is LTI System and why we always prefer LTI system?

Ans: Systems that follow superposition and homogeneity property is Linear and system whose response is not time dependent in Time Invariant.  System satisfies both is LTI system

55)Why we need causal system to implement

Ans: System is causal whose output depends on present or/and past value only not on future. So causal system is not realizable

56)Difference between mobile and a cell phone.

Ans: A mobile phone is the type of cellular phone that is installed in a motor vehicle. There are three main types of cellular phones mobile, transportable, and portable. A mobile unit is attached to the vehicle, draws its power from the vehicles battery and has an external antenna.

57) What is modulation? And where it is utilized?

Ans: modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted.

Analog TV systems: to transmit color information

Two way radio

Analog TV broadcast systems

Wireless broadcasting systems

ATSC digital television standard

Radio broadcasting

Used in cable communication for the transmission of DTV and internet traffic between cable modem and modem termination systems.

V-32 Telephone data/fax modems Satellite transmission of DTVB programs

58) Explain Full duplex and half duplex mode.

Ans: A half-duplex (HDX) system provides communication in both directions, but only one direction at a time (not simultaneously).

A full-duplex (FDX), or sometimes double-duplex system, allows communication in both directions, and, unlike half-duplex, allows this to happen simultaneously. Land-line telephone networks are full-duplex, since they allow both callers to speak and be heard at the same time,

59) Explain Shanon-hartley law.

Ans: In information theory the Shannon–Hartley theorem tells the maximum rate at which information can be transmitted over a communications channel of a specified bandwidth  in the presence of noise. It is an application of the noisy channel coding theorem to the archetypal case of a continuous-time analog communications channel

60) Which type of modulation is used in TV transmission?

Ans: In television system for video transmission AM is used and for audio transmission FM is used....

61) Difference between FM and AM, which is preferred & its advantages.

Ans:

	AM	FM
Origin:	AM method of audio transmission was first successfully carried out in the mid 1870s.	FM radio was developed in the United states mainly by Edwin Armstrong in the 1930s.
Modulating differences:	In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted.	In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted.
Importance:	It is used in both analog and digital communication and telemetry.	It is used in both analog and digital communication and telemetry.
Pros and cons:	AM has poorer sound quality compared to FM, but is cheaper and can be transmitted over long distances. It has a smaller bandwidth so it can have more stations available in any frequency range.	FM is less prone to interference than AM. However, FM signals are impacted by physical barriers. FM has greater sound quality due to higher bandwidth.
Stands for:	AM stands for Amplitude Modulation	FM stands for Frequency Modulation
Range:	AM radio ranges from 535 to 1705 kilohertz (OR) Up to 1200 Bits per second	FM radio ranges in a higher spectrum from 88 to 108 megahertz. (OR) 1200 to 2400 bits per second
Bandwidth Requirements:	Twice the highest modulating frequency. In AM radio broadcasting, the modulating signal has bandwidth of 15kHz, and hence the bandwidth of an amplitude-modulated signal is 30kHz	Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth required is 180kHz
Zero crossing in modulated signal:	Equidistant	not equidistant
Complexity:	transmitter and receiver are simple but in case of SSBSC AM carrier syncronization is needed	tranmitter and reciver are more complex as variation of modulating signal has to converted and detected from corresponding variation in frequencies.(i.e. voltage to frequency and frequency to voltage conversion has to be done) which are quite complex
Noise:	AM is more susceptible to noise because noise affects amplitude, which is where information is "stored" in an AM signal.	FM is less susceptible to noise because information in an FM signal is transmitted through varying the frequency, and not the amplitude.

62)What do you understand by microwaves? why these are called micro

Ans: The term microwave refers to electromagnetic energy having a frequency higher than 1gigahertz (billions of cycles per second), corresponding to wavelength shorter than 30 centimeters.

Microwave signals propagate in straight lines and are affected very little by the troposphere. They are not refracted or reflected by ionized regions in the upper atmosphere. Microwave beams do not readily diffract around barriers such as hills, mountains, and large human-made structures. Some attenuation occurs when microwave energy passes through trees and frame houses. Radio-frequency (RF) energy at longer wavelengths is affected to a lesser degree by such obstacles.

The microwave band is well suited for wireless transmission of signals having largebandwidth. This portion of the RF electromagnetic radiation spectrum encompasses many thousands of megahertz. Compare this with the so-called shortwave band that extends from 3 MHz to 30 MHz, and whose total available bandwidth is only 27 MHz. In communications, a large allowable bandwidth translates into high data speed. The short wavelengths allow the use of dish antennas having manageable diameters. These antennas produce high power gain in transmitting applications, and have excellent sensitivity and directional characteristics for reception of signals.

63) How do microwave oven works??

Ans. A microwave oven works by passing non-ionizing microwave radiation through the food. Microwave radiation is between common radio and infrared frequencies, being usually at 2.45 gigahertz (GHz)—a wavelength of 122 millimetres (4.80 in)—or, in large industrial/commercial ovens, at 915 megahertz (MHz)—328 millimetres (12.9 in). Water, fat, and other substances in the food absorb energy from the microwaves in a process called dielectric heating. Many molecules (such as those of water) are electric dipoles, meaning that they have a partial positive charge at one end and a partial negative charge at the other, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. Rotating molecules hit other molecules and put them into motion, thus dispersing energy. This energy, when dispersed as molecular vibration in solids and liquids (i.e., as both potential energy and kinetic energy of atoms), is heat.

64)Which range of signals are used for terrestrial transmission?

Ans. VLF , LF and MF.

65)Why we use vestigial side band (VSB-C3F) transmission for picture?

Ans.  Bandwidth of picture signal is very large, hence cannot be transmitted by DSB-SC. Also they include low frequency components, thus SSB cant be used. Therefore, VSB is the most apt technique.

66) For asynchronous transmission, is it necessary to supply some synchronizing pulses additionally or to supply or to supply start and stop bit?

Ans. asynchronous transmission does not required any synchronizing pulses , instead it needs start and stop bit  to acknowledge the first and last bit of the data which is transmitted.

67) Difference between C and HDL language.

Ans: A hardware description language looks much like a programming language such as C; it is a textual description consisting of expressions, statements and control structures. One important difference between most programming languages and HDLs is that HDLs explicitly include the notion of time.C is a high level language that is compiled into machine language for specific system.

The system implements some sort of state machine that can process the compiled machine language. 

In VHDL you have to design the state machine itself. Furthermore VHDL is compiled into logic primitives that could be built by logic gates which itself could be realized with transistors. 

C is a programming language. VHDL is a hardware description language.

68) Draw a latch using 2:1 mux.

69)In CMOS, maximum fanout depends on which factors?

Ans: CMOS switching circuits are limited by the charging and discharging times associated with the output resistance of the driving gate and the input capacitance of the load gates. Thus, CMOS fan-out depends on the frequency of switching.

70)what is the difference between "begin-end" and "fork-join"?

Ans: begin -end is sequential while fork- join is for parallel statements.

71) What is body effect?

Ans: In general multiple MOS devices are made on a common substrate. As a result, the substrate voltage of all devices is normally equal. However while connecting the devices serially this may result in an increase in source-to-substrate voltage as we proceed vertically along the series chain (Vsb1=0, Vsb2 0).Which results Vth2>Vth1. 

72) What is difference between mealy and moore machine.

Ans:In the Moore finite state machine model output depends only on the present state. but in the mealy model the output depends on the both present state and the input. 

73)What are the modes of operation of MOS transistor.

Ans:The operation of a MOSFET can be separated into three different modes, depending on the voltages at the terminals. For an enhancement-mode, n-channel MOSFET, the three operational modes are:

·         Cutoff, subthreshold, or weak-inversion mode

·         Linear mode

·         Active mode

74)what do you understand by VLSI?Why we need it?

Ans: Very-large-scale integration (VLSI) is the process of reating integrated circuits by combining thousands of transistors into a single chip. VLSI began in the 1970s when complexsemiconductor and communication technologies were being developed. The microprocessor is a VLSI device.

75) Why is the substrate in NMOS connected to ground and in PMOS to VDD?

Ans: Because Drain and Souce same type semiconductor, substrate is opposite type. Substrate produce diode with source and drain and we can bloke this diode by Source-Substrate connection else this diode conduct and mosdont work.

76)What is latch-up in CMOS design and what are the ways to prevent it.

Ans: A byproduct of the Bulk CMOS structure is a pair of parasitic bipolar transistors. The collector of each BJT is connected to the base of the other transistor in a positive feedback structure. A phenomenon called latchup can occur when (1) both BJT's conduct, creating a low resistance path between Vdd and GND and (2) the product of the gains of the two transistors in the feedback loop, b1 x b2, is greater than one. The result of latchup is at the minimum a circuit malfunction, and in the worst case, the destruction of the device.

77) What is Noise Margin? Explain the procedure to determine Noise Margin

Ans: In digital logic design the general representation of input and output are High and low level (1's and 0's). In actual case when the input signal transitions the output switches  to full swing before the input has reached its full swing. 

The minimum signal level to get a out put High or low is called VIH, VIL (For inversion stage Input for getting full output low swing and input for getting full output high swing). For the interoperability of this logic device i.e. to use tihs output directly to feed into next stage without level shifting the VIL > VOL, similarly VIH < VOH. In such condition when logic swing VIL is enough to get full swing on Output the noise margin will be VOL-VIL. Similarly NM for signal transitioning high is VOH-VIH.

78)Implement NOR gate using CMOS.

79)What is FPGA and its application?

Ans: A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturing—hence "field-programmable". The FPGA configuration is generally specified using a hardware description language (HDL), similar to that used for an application-specific integrated circuit (ASIC) (circuit diagrams were previously used to specify the configuration, as they were for ASICs, but this is increasingly rare). Contemporary FPGAs have large resources of logic gates and RAM blocks to implement complex digital computations.Applications of FPGAs include digital signal processing, software-defined radio, ASIC prototyping, medical imaging, computer vision, speech recognition, cryptography, bioinformatics, computer hardware emulation, radio astronomy, metal detection and a growing range of other areas.

80) Design OR gate using 2:1 MUX.

81)What is difference between intial and always statements in verilog?

Ans: Always block starts at simulation time 0 and repeats forever with changes in elements in sensitivity list. Execution of statement starts from begin and stops only when wait statement in encountered.it is synthesizable construct of verilog.

An initial block does not have a sensitivity list while always block may or may not have a sensitivity list. However no sensitivity list would create a mismatch in simulation and synthesis for always block.

82)What is the Reverse link and Forward link frequency of GSM 900.

Ans: Reverse Link : 890-915 Mhz    Forward Link : 935-960 Mhz

83)What do you mean by Multipath Fading.

Ans:- Multipath fading is caused by interference between two or more replicas of input signal being received by receiver. These multiple copies may be shifted in phase, frequency, amplitude & time.

84)What is the effect of decreasing the antenna height on the transmission system.

Ans. Decreasing the antenna height will increase the effect of reflection, scattering, refraction & diffraction in the channel.

85)What is the effect of decreasing the cluster size on the system performance.

Ans. Decrease in cluster size will led to increase in interference between co-channel cells. It also increase the system capacity.

86)What do you mean by Soft Handoff.

Ans. This type of handoff generally happens in CDMA (IS-95). In this the channel used by moving user will be kept fixed i.e there is no physical transition of channel as the user move from one cell to another.

87)How the variations of distance between Transmitter and Receiver effect the system performance.

Ans. As the distance between tx and rx decreases power level received by the rx will be increased. But as we goes on increasing the distance between tx and rx the power level received by rx will keep on decreasing.

88)What is the difference between Rayleigh Distribution and Rician Distribution.

Ans. The only difference between Rayleigh and Rician channel is that there is no Component from LOS path present in Rayleigh distribution, whereas in Rician distribution Component from LOS path is available.

89)What is the difference between Fast and Slow fading.

Ans. In Fast fading the channel’s impulse response is varying at rate less than symbol rate. Whereas in slow fading the channel’s impulse response is varying at rate greater than symbol rate.

90)What is the motive of EIR in GSM system.

Ans. The motive of EIR in GSM is to check the authenticity of Mobile Equipment.

91)What do you mean by GMSK.

Ans. GMSK means Gaussian Minimum Shift Keying. It is a combination of gaussion filter followed by MSK Modulator.

92)Why MSK is know as MSK.

Ans. MSK (Minimum Shift Keying) is known as MSK, Because the frequency shift intorudce by this modulation is the minimum frequency shift required for two FSK signals to be Orthogonal.

93)What is the effect of increasing the value of M on performance of M-PSK.

Ans. When we increase the value of M in M-PSK it will increase the data capacity of the system. But it also increase the probability of BER, because it reduces the spacing between adjacent constellation points.