8/7/2019 chan viva

1/41

A Report about

COMPHRAHENSIV VIVA

Submitted By

CHANDRA MOHAN REDDY

(Hall Ticket No.: 07D11A0460)

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS AND COMMUNICATION ENGINEERING

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

TRR ENGINEERING COLLEGE

(An ISO 9000: 2000 Certified Institution)

AFFILIATED TO JAWAHARLAR NEHRU TECHNOLOGICAL UNIVERSITY

HYDERABAD

2007 - 2011

8/7/2019 chan viva

2/41

MICROPROCESSORS AND INTERFACING

1.What are Macros?

Ans. Macro is a group of instruction. The macro assembler generates the code in the program

each time where the macro is called. Macros are defined by MACRO & ENDM directives.

Creating macro is similar to creating new opcodes that can be used in the program

INIT MACRO

MOV AX, data

MOV DS

MOV ES, AX

ENDM

2. Explain how IRET instruction is executed?

A. The IERT instruction is used at the end of the interrupt service routine to return execution to

the interrupted program . The 8086 copies return address from stack into IP and CS registers and

the stored value of flags back to the flag register .The RET instruction does not copy the flags

from the stack back to the flag register.

3. What is the loop instructions of 8086?

A. The loop instructions cause the microprocessor to execute a series of instructions repeatedly.

Decrements CX by one without affecting flags and performs short jump to the target address if

CX is not equal to zero. Loop uses relative addressing mode.

MOV CX,0064H ;Initilize counter with 100^10

BACK : ------ ; This section is

------ ; executed 100

------ ; times,i.e.,

LOOP BACK ; until CX=0

4. What are the features of 8255 PPI?

Ans. Three 8-bit Peripheral Ports - Ports A, B, and C

8/7/2019 chan viva

3/41

Three programming modes for Peripheral Ports: Mode 0 (Basic Input/Output),

Mode 1 (Strobed Input/Output), and Mode 2 (Bidirectional)

Total of 24 programmable I/O lines 8-bit bidirectional system data bus with standard microprocessor interface

Controls.

5. What is Interrupt?

Ans. The meaning of interrupts is to break the sequence of operation.While the cpu is

executing a program,on interrupt breaks the normal sequence of executionof instructions,

diverts its execution to some other program called Interrupt Service Routine (ISR).After

executing ISR , the control is transferred back again to the main program.

6. what is type 2 interrupt?

A. Non Maskable interrupt is the type 2 interrupt. This interrupt cannot be displayed by any

software instruction. This interrupt is activated by low to high transition on 8086 NMI input pin.In response, 8086 will do a type 2 interrupt.

7. what are the types of data communication in 8251?

A. 1. Asynchronous transmission

2. Asynchronous reception

3. Synchronous transmission

4. Synchronous reception

8. Register Set of 8051-SFR?

Ans. Register Set of 8051-SFR

TH0-TL0 and TH1-TL1

16 bit timer registers

P0-P3 port latchesSP, PSW, IP Interrupt Priority, IE enable

TCON timer/counter control reg to turn on/off the timers, interrupt control flags for ext. int

like INT1 and INT0

TMOD modes of operation of timer/counter

SCON serial port mode control reg

8/7/2019 chan viva

4/41

SBUF serial data buffer for transmit and receive

PCON Power control reg power down bit, idle bit

MICRO CONTROLLERS AND APPLICATIONS

1. What are 8051 microcontrollers Internal and External memories?

Ans. The 8051 has three very general types of memory. To effectively program the 8051 it isnecessary to have a basic understanding of these memory types.

The memory types are illustrated in the following graphic. They are: On-Chip Memory, External

Code Memory, and External RAM.

On-Chip Memory refers to any memory (Code, RAM, or other) that physically exists on themicrocontroller itself. On-chip memory can be of several types, but we'll get into that shortly.

External Code Memory is code (or program) memory that resides off-chip. This is often in the

form of an external EPROM

External RAM is RAM memory that resides off-chip. This is often in the form of standard static

RAM or flash RAM.

2. How do having separate caches for instruction, data and branch help?

A. There are 3 structural units provided in a processor have separate cauches for instruction, data

and branch. They are,

1. I-cache (Instruction cache)

2. D-cache (Data cache)

3. BT cache (Branch transfer/Branch target cache).

3. 8051 microcontroller interrupts?

Ans. 8051 provides 5 vectored interrupts. They are -

1.

2. TF03.

4. TF1

5. RI/TI

8/7/2019 chan viva

5/41

Out of these, and are external interrupts whereas Timer and Serial port interrupts are

generated internally. The external interrupts could be negative edge triggered or low level

triggered. All these interrupt, when activated, set the corresponding interrupt flags. Except forserial interrupt, the interrupt flags are cleared when the processor branches to the Interrupt

Service Routine (ISR). The external interrupt flags are cleared on branching to Interrupt Service

Routine (ISR), provided the interrupt is negative edge triggered. For low level triggered externalinterrupt as well as for serial interrupt, the corresponding flags have to be cleared by software by

the programmer.

4. What is Free running counter in 8051?

Ans. The Counter Free-Running block counts up until reaching the maximum value, 2Nbits 1,

where N bits is the number of bits. Then the counter overflows to zero and begins counting upagain.

After overflow, the counter always initializes to zero. However, if you select the global doubles

override, the Counter Free-Running block does not wrap back to zero.

5. How printer inter faces to 8051MCU?

Ans. Printer has 8 data lines, and we use two control signals, busy and strobe. Busy pin is madeinput and strobe as output. First strobe pin is kept high, data to be printed is obtained at particular

port then, low to high transition is given to the strobe. then we keep checking the busy pin, if

printer is busy then wait, after it becomes free then send next data. for printer interfacing weused DB25 connector.

6. What is Real-Time Operating Systems in Microcontrollers?

Ans. Real-time embedded systems serve various purposes, such as to control or process data. A

real-time operating system is a piece of software with a set of APIs that developers can use tobuild applications. RTOSs support the need of some embedded systems to meet deadlines.

However, using an RTOS doesn't guarantee that a system will always meet the deadlines,

because these systems also depend on the overall system's design. Although RTOSs for

embedded systems are predominantly used in high-end microprocessors or microcontrollers with32-bit CPUs, there is a growing trend to provide these features in mid-range (16-bit and 8-bit)

processor systems

7. What are the interrupt vector tables present in the memory map of 80196 family?

A. There are 2 types of interrupt vector tables. They are

1. Lower interrupt vector table

2. Upper interrupt vector table

8/7/2019 chan viva

6/41

8. What are the addressing modes of ARM MCU?

A. The different addressing modes present in ARM MCU are,

1. Register addressing

2. Immediate addressing

3. Indirect base and indexed addressing.

NETWORK ANALYSYS

1. What is Voltage and Current Sources?

Ans. Real voltage sources can be represented as ideal voltage sources in series with a

resistance r, the ideal voltage source having zero resistance. Real current sources can be

represented as ideal current sources in parallel with a resistance r, the ideal current sourcehaving infinite resistance.

2. Define Mutual Induction ?

Ans. The changing magnetic field created by one circuit (the primary) can induce a

changing voltage and/or current in a second circuit (the secondary).

The mutual inductance, M, of two circuits describes the size of the voltage in the secondaryinduced by changes in the current of the primary:

change in I (primary)

V(secondary) = - M * ----------------------

change in time

The units of mutual inductance are henry, abbreviated "H".

3. Define bandwidth?

Ans. The bandwidth of an accelerometer refers to it's useful range of operating frequencies.This is usually defined by the frequency where the amplitude ratio falls to 0.5, the 3 dB point.

4. Define Independent Voltage &?

Ans. An ideal independent voltage source is a two-terminal circuit element where the voltageacross ita) is independent of the current through it

b) can be specified independently of any other variable in a circuit.

5. Maximum Power Transfer Theorem?

8/7/2019 chan viva

7/41

Ans..Maximum Power Transfer is another useful analysis method to ensure that the

maximum amount of power will be dissipated in the load resistance when the value of the

load resistance is exactly equal to the resistance of the power source. The relationshipbetween the load impedance and the internal impedance of the energy source will give the

power in the load.

6. What is H - Parameters fortwo-port network?

Ans.A two-port network(a kind offour-terminal networkorquadripole) is an electrical

network or device with two pairs of terminals connected together internally by an electrical

network. Two terminals constitute a port if they satisfy the essential requirement known as

the port condition: the same current must enter and leave a port.

7. What is Laplace Transform?

Ans. By applying the Laplace transform, one can change an ordinary differential equation into an

algebraic equation, as algebraic equation is generally easier to deal with. Another advantage ofLaplace transform is in dealing the external force is either impulsive , (the force lasts a very shottime period such as the bat hits a baseball) or the force is on and off for some regular or irregular

period of time.

8. What is M-derived filter?

Ans. M-derived filters orm-type filters are a type of electronic filter designed using the imagemethod. They were invented by Otto Zobel in the early 1920s. This filter type was originally

intended for use with telephone multiplexing and was an improvement on the existing constant k

type filter.

CONTROL SYSTEMS

1. what is Open control systems?

Ans. In Open-Loopcontrol, no feedback loop is employed and system variations which cause

the output to deviate from the desired value are not detected or corrected.

2. How do you construct a signal flow graph from the equations?

A. 1. Represent each variable in algebraic equations as a separate node.2. By using the property of signal flow graph, that the value of any variable (node) is equal to

the algebraic sum of entering a signals which are connected to that node.3. Coefficients of the variables in the algebraic equations are to be represented as the branch

gains, which are connecting nodes in the signal flow graph.

4. Show the input and output variables as separate nodes i.e., input node(source)and output

node(sink)respectively.

3. The important time response specification of a standard second ordered system to a unit

8/7/2019 chan viva

8/41

step input?

A. 1. Delay time (Td)

2. Rise time (Tr)3. Peak time (Tp)

4. Peak overshoot (Mp)

5. Setting time (Ts)

4. What are the limitations of Routh-Hurwitz Criterion?

A. 1. This criterion is applicable to only linear and time-invariant systems.

2. This criterion is valid only for characteristics equation which is having real coefficients.

3. This criterion does not give exact locations of the closed loop poles of the system.

4. This criterion does not provide any method to stabilise an unstable system.

5. What is Gain margin?

Ans. The gain margin is the amount of gain increase required to make the loop gain unity at the

frequency where the phase angle is 180. In other words, the gain margin is 1/gifgis the gainat the 180 phase frequency. Similarly, the phase margin is the difference between the phase of

the response and 180 when the loop gain is 1.0.

6. What is Nyquist Plots?

Ans. There are a number of polar graph options for studying control systems including the

nyquist, inverse polar plot and the nichols plot. The nyquist open loop polar plot indicates thedegree of stability, and the adjustments required and provides stability information for systems

containing time delays. Polar plots are not used exclusively because,without powerful

computing facilities, they can be difficult to generate at a detailed level and they do not directlyyield frequency values.

7. What is leadlag compensator ?

Ans. A leadlag compensator is a component in a control system that improves an undesirable

frequency response in a feedback and control system. It is a fundamental building block in

classical control theory.

8. What is state variables?

Ans. In Control Engineering and other areas of science and engineering, state variables are usedto represent the states of a general system. The state variables can be used to describe the state

space of the system. The equations relating the current state and output of a system to its current

input and past states are called the state equations. The state equations for a linear time invariantsystem are expressed with Coefficient matrices.

COMPUTER ORGANIZATION

8/7/2019 chan viva

9/41

1. What is digital computer?

A. Computer is an programmable machine designed to read and execute sequentially a list ofinstructions that make it perform arithmetical and logical operations on binary numbers.

2. What is micro-operation?

A. Complex digital systems which deals with lots of tasks like logic operation, arithmetic

operation contains many hardware whose are interconnected among them is called micro-operation.

3. Explain the functions of control unit?

A. The functions of the control unit are as follows,

1. Sequencing of Micro-operations.

2. Execution of Micro-operations

(a) Hardwired control unit.(b) Micro-programmed control unit.

4. What is decimal arithmetic unit ?

Ans. A decimal arithmetic unit is a digital function that performs decimal micro-operations. It

can add or subtract decimal numbers, usually by forming the 9's or 10'scomplement of thesubtrahend. The unit accepts coded decimal numbers and generates results in the same adopted

binary code. A single-stage decimal arithmetic unit consists of nine binary input variables and

five binary output variables, since a minimum of four bits is required to represent each codeddecimal digit. Each stage must have four inputs for the augend digit, four inputs for the addend

digit, and an input-carry. The outputs include four terminals for the sum digit and one for the

output-carry. Of course, there is a wide variety of possible circuit configurations dependent onthe code used to represent the decimal digits.

5. What is Cache Memory?

Ans. A CPU cache is a cache used by the central processing unit of a computer to reduce the

average time to access memory. The cache is a smaller, faster memory which stores copies of the

data from the most frequently used main memory locations. As long as most memory accesses

are cached memory locations, the average latency of memory accesses will be closer to the cache

latency than to the latency of main memory.

6. What are Peripheral devises?

Ans. Peripheral devices can be classified according to their functions.

Input: Input devices are the type of the computer devices that are used to provide the control

signals to the computer. Keyboard and the Mouse are the examples of the input devices.

8/7/2019 chan viva

10/41

Output: Output devices are the devices that are used to display the results. Printer, scanner,

speaker and the monitor are the examples of the output devices.

Storage: A storage device is a device that is used to store the input.

7. What is Parallel processing?

Ans. Parallel processing is the simultaneous processing of the same task on two or

more microprocessors in order to obtain faster results. The computer resources can include a

single computer with multiple processors, or a number of computers connected by a network, ora combination of both. The processors access data through shared memory. Some

supercomputer parallel processing systems have hundreds of thousands of microprocessors.

8. What is Interconnection Structures?

Ans. A computer consists of a set of components(CPU, memory, I/O) that communicate with

each other.

The collection of paths connecting thevarious modules is call the Interconnection Structures.The design of this structure will depend onthe exchange that must be made between

Modules.

ELECTRONIC DEVICES & CIRCUITS

1. What are Electric and Magnetic fields

Ans. Wherever there is electricity, there are also electric and magnetic fields, invisible lines offorce created by the electric charges. Electric fields result from the strength of the charge while

magnetic fields result from the motion of the charge, or the current.

2. What is the equation of TUF?

A. The full form of TUP is

Transformer Utilization Factor

TUF=Pd.c/Pa.c (rating)

3. What are the different configurations of BJT?

A. The three different types of BJT configurations are,

8/7/2019 chan viva

11/41

i. Common base configuration

ii. Common emitter configuration

iii. Common collector configuration.

4. What is biasing?

A. The process of obtaining desired Q-point by giving proper supply voltage and resistance is

known as biasing.

5. What is Thermal runaway in BJT?

Ans. Leakage current increases significantly in bipolar transistors (notably germanium-basedbipolar transistors) as they increase in temperature. Depending on the design of the circuit, this

increase in leakage current can increase the current flowing through the transistor and with it thepower dissipation.

6. What is input impedance?

Ans. The input impedance of an electrical network is the equivalent impedance "seen" by apower source connected to that network. If the source provides known voltage and current, such

impedance can be calculated using Ohm's Law. The input impedance is the Thvenin's

equivalent circuit of the electrical network, modeled by an RL (resistor-inductor) or an RC(resistor-capacitor) combination, with equivalent values that would result in the same response as

that of the network. It is also called Z11 in terms of Z-Parameters.

7. What is amplifier gain?

Ans. Amplifier gain stands for any of Voltage amplifier, Current amplifier, Trans resistanceTrans admittance amplifier

0

0

; ;1

f

f

i

XXAA A

A X X

= = =

+

8/7/2019 chan viva

12/41

+

Ve feed back amplifier depends on |1 | 1 , 1b bA ve f ve f + > < +

Feed back reduces noise distortion, gain variation due to parameters, increases BW.

( )1 A+ is called de-sensitivity factor.

8. What is Wein Bridge oscillator?

Ans. A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can

generate a large range of frequencies. The circuit is based on an electrical network originally

developed by Max Wien in 1891. The bridge comprises four resistors and two capacitors. It can

also be viewed as a positive feedback system combined with a band pass filter. Wien did not

have a means of developing electronic gain so a workable oscillator could not be realized.

Classic Wien bridge oscillator

PULSE AND DIGITAL CIRCUITS

1. What is high pass RC circuit?

A. A circuit which allows high-frequency signals and attenuates or stops the low-frequency

signals is called high-pass RC circuit.

2. Explain the non-linear wave shaping?

A. The process where by the form of a sinusoidal or non-sinusoidal signal is altered by

transmitting through a non-linear network is called non-linear wave shaping.

8/7/2019 chan viva

13/41

There are 2 types of non-linear wave shaping techniques,

1. Clipping

2. Clamping.

3. What is transistor switch?

A. The transistor acts as a switch when it is placed in series with the load and supply voltage.

4. What is multi-vibrator?

A. A multi-vibrator is an electronic circuit used to implement a variety of simple two-state

systems such

as oscillators,timersand flip-flops.

5. What is a voltage time base generator?

Ans. A "function generator" generates a voltage equal to some function of time. The most basic

models will produce sine, square, and sawtooth waves at different frequencies, but the more

expensive models will do all kinds of waves.

6. What is monostable muiltivibrator?

Ans. Monostable Multivibrators or "one-shot" pulse generators are used to convert short sharp

pulses into wider ones for timing applications. Monostable multivibrators generate a single

output pulse, either "high" or "low", when a suitable external trigger signal or pulse T is applied.This trigger pulse signal initiates a timing cycle which causes the output of the monostable to

change state at the start of the timing cycle, (t1) and remain in this second state until the end of

the timing period, (t1) which is determined by the time constant of the timing capacitor, CT and

the resistor, RT.

7. What is sampling gates?

Ans. sampling gates are transmission circuits in which the output is an exact replica of input

wave from during that selected time interval and is zero otherwise

that means only for selected time period the output remains same and for remaining time period

the output is zero.

8. What is Diodetransistor logic (DTL)?

http://www.answers.com/topic/electronic-circuit-1http://www.answers.com/topic/oscillationhttp://www.answers.com/topic/oscillationhttp://www.answers.com/topic/timerhttp://www.answers.com/topic/timerhttp://www.answers.com/topic/flip-flop-electronicshttp://www.answers.com/topic/flip-flop-electronicshttp://www.answers.com/topic/electronic-circuit-1http://www.answers.com/topic/oscillationhttp://www.answers.com/topic/timerhttp://www.answers.com/topic/flip-flop-electronics

8/7/2019 chan viva

14/41

Diodetransistor logic (DTL) is a class of digital circuits built from bipolar junction transistors

(BJT), diodes and resistors, it is the direct ancestor of transistortransistor logic. It is calleddiodetransistor logic because the logic gating function (e.g., AND) is performed by a diodenetwork and the amplifying function is performed by a transistor

LINEAR IC APPLICATIONS

1.Mention the advantages of integrated circuits.

Ans.

*Miniaturisation and hence increased equipment density.

*Cost reduction due to batch processing.

*Increased system reliability due to the elimination of soldered joints.*Improved functional performance.

*Matched devices.

*Increased operating speeds.

*Reduction in power consumption.

2. Define an operational amplifier.

Ans. An operational amplifier is a direct-coupled, high gain amplifier consisting of one or more

differential amplifier. By properly selecting the external components, it can be used to perform avariety of mathematical operations.

3. What is the need for an instrumentation amplifier?

Ans. In a number of industrial and consumer applications, the measurement of physical

quantities is usually done with the help of transducers. The output of transducer has to beamplified So that it can drive the indicator or display system. This function is performed by an

instrumentation amplifier.

4. What do you mean by a precision diode?

Ans. The major limitation of ordinary diode is that it cannot rectify voltages below the cut in

voltage of the diode. A circuit designed by placing a diode in the feedback loop of an op amp iscalled the precision diode and it is capable of rectifying input signals of the order of millivolt.

5. What are the demerits of passive filters?

Ans. Passive filters works well for high frequencies. But at audio frequencies, the inductors

become problematic, as they become large, heavy and expensive. For low frequency

applications, more number of turns of wire must be used which in turn adds to the seriesresistance degrading inductors performance ie, low Q, resulting in high power dissipation.

6. Define capture range of a PLL?

8/7/2019 chan viva

15/41

Ans. The range of frequencies over which the PLL can acquire lock with an input signal is called

the capture range. It is expressed as a percentage of the VCO free running frequency.

7. Explain in brief the principle of operation of successive Approximation ADC?

Ans. The circuit of successive approximation ADC consists of a successive approximation

register (SAR), to find the required value of each bit by trial & error. With the arrival of START

command, SAR sets the MSB bit to 1. The O/P is converted into an analog signal & it iscompared with I/P signal. This O/P is low or High. This process continues until all bits are

checked.

8. What is meant by delta modulation?

Ans. Delta modulation is a technique capable of performing analog signal quantization with

smaller bandwidth requirements. Here, the binary output representing the most recent sampledamplitude will be determined on the basis of previous sampled amplitude levels.

DIGITAL IC APPLICATIONS

1. What is CMOS?

Ans. CMOS gates are all based on the fundamental inverter circuit shown to the left. Note thatboth transistors are enhancement-mode MOSFETs; one N-channel with its source grounded, and

one P-channel with its source connected to +V. Their gates are connected together to form theinput, and their drains are connected together to form the output.

2. What is TTL logic?

Ans.TTL devices make use of bipolar transistors. The main distinguishing features of the basicTTL family is that they demand a power rail which is very close to +5V, and they use a relatively

high amount of current to drive their logic levels (below 1V for a logical 0 or low, and above

about 3.5V for a logical 1 or high).

3. What are Functions and Procedures?

Ans. Functions and procedures in VHDL, which are collectively known as subprograms, aredirectly analogous to functions and procedures in a high-level software programming language

such as C or Pascal. A procedure is a subprogram that has an argument list consisting of inputs

and outputs, and no return value. A function is a subprogram that has only inputs in its argumentlist, and has a return value.

8/7/2019 chan viva

16/41

4. What is Structural design elements?

Ans. A VHDL architecture that uses components is often called a structural description or

Structural design.The important features of structural type of architecture body are,

Design hierarchy

Components are used

Each component is simulated separatelyIn structural modeling, an entity is described as a set of components connected by signals,

that is, as a net list. The components used in an architecture may be form a library or may be

ones that were previously defined as part of design.

5. What is a decoder?

Ans. A decoder is a device which does the reverse of an encoder, undoing the encoding so that

the original information can be retrieved. The same method used to encode is usually justreversed in order to decode.

6. What is Barrel Shifter?

Ans. A barrel shifter is a digital circuit that can shift a data word by a specified number of bits

in one clock cycle. It can be implemented as a sequence of multiplexers (mux.), and in such an

implementation the output of one mux is connected to the input of the next mux in a way thatdepends on the shift distance.

7. What is a shift register?

Ans. In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, which

has the output of any one but the last flip-flop connected to the "data" input of the next one in thechain, resulting in a circuit that shifts by one position the one-dimensional "bit array" stored in it,

shifting in the data present at its input and shifting outthe last bit in the array, when enabled to

do so by a transition of the clock input.

8. What is SRAM?

Ans. Static random-access memory (SRAM) is a type of semiconductor memory where theword static indicates that, unlike dynamic RAM (DRAM), it does not need to be periodically

refreshed, as SRAM uses bistable latching circuitry to store each bit. SRAM exhibits dataremanence, but is still volatile in the conventional sense that data is eventually lost when thememory is not powered.

VLSI DESIGN

8/7/2019 chan viva

17/41

1. What is BiCMOS?

Ans. BiCMOS technology is a combination of Bipolar and CMOS technology. CMOS

technology offers less power dissipation, smaller noise margins, and higher packing density.

Bipolar technology, on the other hand, ensures high switching and I/O speed and good noiseperformance.

2. What is Bi-CMOS Inverters?

Ans. Two bipolar transistors (T3 and T4), one nMOS and one pMOS transistor (both

enhancement-type devices, OFF at Vin=0V)

The MOS switches perform the logic function & bipolar transistors drive output loads

Vin = 0 :

T1 is off. Therefore T3 is non-conducting

T2 ON - supplies current to base of T4

T4 base voltage set to Vdd.

T4 conducts & acts as current source to charge load CL towards Vdd.

Vout rises to Vdd - Vbe (of T4)

8/7/2019 chan viva

18/41

Note : Vbe (of T4) is base-emitter voltage of T4.

(pullup bipolar transistor turns off as the output approaches

5V - Vbe (of T4))

Vin = Vdd :

T2 is off. Therefore T4 is non-conducting.

T1 is on and supplies current to the base of T3

T3 conducts & acts as a current sink to discharge load CL towards 0V.

Vout falls to 0V+ VCEsat (of T3)

Note : VCEsat (of T3) is saturation V from T3 collector to emitter.

3. What is Stick diagram?

Ans. Stick diagrams are commonly used to represent the topology (not the geometry) of CMOSintegrated circuits. With a little annotation (FET width and length) they provide adequateinformation to guide layout and mask generation.Stick diagrams help plan layout quickly Need not be to scale Draw with color pencils or dry-erase marker

4.Give the basic process for IC fabrication?

Ans.

Silicon wafer Preparation

Epitaxial Growth

Oxidation

Photolithography

Diffusion

Ion Implantation

Isolation technique

Metallization

Assembly processing & Packaging

5. What are gate primitives?

Ans. Verilog supports basic logic gates as predefined primitives. Primitive logic functionkeyword provide the basics for structural modeling at gate level. These primitives are

instantiated like modules except that they are predefined in verilogand do not need a module

definition. The important operations are and, nand, or, xor, xnor, and buf(non-inverting drivebuffer).

6. What is a FPGA?

8/7/2019 chan viva

19/41

Ans. A field programmable gate array (FPGA) is a programmable logic device that supports

implementation of relatively large logic circuits. FPGAs can be used to implement a logic circuit

with more than 20,000 gates whereas a CPLD can implement circuits of upto about 20,000equivalent gates.

7. Write notes on functionality tests?

Ans. Functionality tests verify that the chip performs its intended function. These tests assert that

all the gates in the chip, acting in concert, achieve a desired function. These tests are usually usedearly in the design cycle to verify the functionality of the circuit..

8. What is fault grading?

Ans. Fault grading consists of two steps. First, the node to be faulted is selected. A simulation is

run with no faults inserted, and the results of this simulation are saved. Each node or line to befaulted is set to 0 and then 1 and the test vector set is applied. If and when a discrepancy is

detected between the faulted circuit response and the good circuit response, the fault is said to bedetected and the simulation is stopped.

PROBABILITY THEORY AND STOCHASTIC PROCESSES

1. Define sample space?

A. A set of all possible distinct events of a random experiment is known as sample space.

Example:

The sample space, when a dice is thrown is {1, 2, 3, 4, 5, 6}.

2. Define continous random variable?

A. If a random variable X takes only of finite or all possible values between certain limits, it is

called a continous random variable.

Example:

Heights, Weights etc.

3. Explain about skew?

A. The skew of the density function is a measure of the symmetry of the probability density

function fx(x) of random variable X about x=m1.

8/7/2019 chan viva

20/41

The skew of a density function is also called as third central movement of the random

variable and is given by,

3= E[(X-m)3].

4. Define conditional probability mass function?

Ans. If A and B are 2 random variables. The conditional probability mass function (or)

conditional density function of the random variable B, given A=a is,

F(b/a)= f(a/b)/g(a), g(a)>0

Where ,

a,b are arbitrary real numbers

f(a,b) is the joint probability density function

g(a) is marginal density function of A=a.

5. Write the properties of Gaussian random variables?

Ans. The properties of Gaussian random variables are given below,

1. The Gaussian random variables are completely defined through only their means, variances

and co-variances.

2. Random variables are said to be statistically independent if they are uncorrelated.

6. Explain the classification of random process?

Ans. Random processes are classified into 4 types according to the characteristics of t and the

random variable X=X(t) at time t. they are,

i. Continous random process

ii. Discrete random process

iii. Continous random sequence

iv. Discrete random sequence.

8/7/2019 chan viva

21/41

7. State any 1 property of PSD?

Ans. For a wide-sense-stationary random process, power spectral density at zero frequency

(=0) gives the area under the graph of auto correlation.

8. What are the different types of noises?

Ans. The various types of noises are,

i. Flicker Noise

ii. Shot Noise

iii. Partition Noise

iv. Thermal Noise.

SIGNALS AND SYSTEMS

1. What is SIGNALS AND CLASSIFICATION OF SIGNALS?

Ans. A signal is a function representing a physical quantity or variable, and typically it contains

information about the behavior or nature of the phenomenon. For instance, in a RC circuit the

signal may represent the voltage across the capacitor or the current flowing in the resistor.

Mathematically, a signal is represented as a function of an independent variable t. Usually t

represents time. Thus, a signal is denoted by x(t).

2. What are the Properties of the Convolution Integral?

Ans. The convolution integral has the following properties.

I. Commutative:

~ ( t* h) ( t )= h ( t )* ~ ( t )

2. Associative:

{ x P )* h l ( 4* h , ( t ) = x ( t )* { h l ( f*) h 2 ( 4)

3. Distributive:x ( t )* { h , ( t ) )+ h N = x ( t )* h l ( t )+ x ( t )* h, ( t )

3. What are Causal and Stable Systems?

Ans. If the system is both causal and stable, then all the poles of H(s) must lie in the left half of

the s-plane; that is, they all have negative real parts because the ROC is of the form Re(s) >a

max, and since the jo axis is included in the ROC, we must have a,, < 0.

8/7/2019 chan viva

22/41

4. Define Z-Transform?

Ans. The function H(z) in Eq. (4.2) is referred to as the z-transform of h[n]. For a general

discrete-time signal x[n], the z-transform X(z) is defined as

mX(Z)= x[n] z - "

n= -OD

( 4 . 3 )

The variable z is generally complex-valued and is expressed in polar form as where r is the

magnitude ofzand R is the angle ofz . The z-transform defined in is often called the bilateral

(ortwo-sided) z-transform in contrast to the unilateral.

5. State parsevals theorem for energy signals?

A. The energy of continous time signal x(t) is,

E=

For energy signal, the average power is zero. Parsevals theorem for energy signals is,

E=

Finally,

E=

6. What is sampling theorem?

A. A continous-time signal can be completely represented in its samples and recovered back, if

the sampling frequency fs is greater than (or) equal to the twice of highest frequency

component of the message signal fm i.e.,

Fs2fm

7. What are the types of system?

A. A system are of three types. They are,

i. Stable system

ii. Unstable system

iii. Marginally stable system.

8/7/2019 chan viva

23/41

8. What are the methods for finding inverse Z-transform?

A. Methods for finding inverse Z-transform are as follows,

i. Power series expansion or long division method

ii. Partial fraction method

iii. Residue method.

DIGITAL SIGNAL PROCESSING

1. What is a continuous and discrete time signal?

Ans.Continuous time signal: A signal x(t) is said to be continuous if it is defined for all time t.

Continuous time signal arise naturally when a physical waveform such as acoustics wave

or light wave is converted into a electrical signal. This is effected by means oftransducer.(e.g.) microphone, photocell.

Discrete time signal: A discrete time signal is defined only at discrete instants of time.

The independent variable has discrete values only, which are uniformly spaced. A

discrete time signal is often derived from the continuous time signal by sampling it at auniform rate.

2. What are time invariant systems?

Ans.

A system is said to be time invariant system if a time delay or advance of the input signal

leads to an idenditical shift in the output signal. This implies that a time invariant systemresponds idenditically no matter when the input signal is applied. It also satisfies the

conditionR{x(n-k)}=y(n-k).

3. Differentiate between DIT and DIF algorithm

Ans.

DIT Time is decimated and input is bi reversed format output in natural order

DIF Frequency is decimated and input is natural order output is bit reversedformat.

4. Distinguish analog and digital filters

Ans.

Analog Filter Digital Filter

1. Constructed using active or Consists of elements like adder,

passive components and it is subtractor and delay units and it is

8/7/2019 chan viva

24/41

described by a differential described by a difference equation

equation

2. Frequency response can be Frequency response can be

changed by changing the changed by changing the filter

components coefficients

3. It processes and generates Processes and generates digital

analog output output

4. Output varies due to external Not influenced by external

conditions conditions

5. What is warping effect?

Ans. For smaller values of w there exist linear relationship between w and .but for larger values

of w the relationship is nonlinear. This introduces distortion in the frequency axis. This effect

compresses the magnitude and phase response. This effect is called warping effect

6. Write the steps involved in FIR filter design?

Ans.

Choose the desired frequency response Hd(w)

Take the inverse Fourier transform and obtain Hd(n)

Convert the infinite duration sequence

7.What is the principle of designing FIR filter using frequency sampling method?

Ans. In frequency sampling method the desired magnitude response is sampled and a linear

phase response is specified .The samples of desired frequency response are defined as DFTcoefficients. The filter coefficients are then determined as the IDFT of this set of samples.

8. List the on-chip peripherals in 5X.

Ans. The C5X DSP on-chip peripherals available are as follows:

1. Clock Generator

2. Hardware Timer3. Software-Programmable Wait-State Generators

4. Parallel I/O Ports

5. Host Port Interface (HPI)

6. Serial Port7. Buffered Serial Port (BSP)

8. Time-Division Multiplexed (TDM) Serial Port

9. User-Maskable Interrupts

DIGITAL IMAGE PROCESSING

1. Define Image?

8/7/2019 chan viva

25/41

Ans. An Image may be defined as a two dimensional function f(x,y) where x & y are spatial

(plane) coordinates, and the amplitude of f at any pair of coordinates (x,y) is called intensity or

gray level of the image at that point. When x,y and the amplitude values of f are all finite,discrete quantities we call the image as Digital Image.

2. Write the expression of one-dimensional discrete Fourier transforms

Ans. Forward transform

The sequence of x(n) is given by x(n) = { x0,x1,x2, xN-1}.X(k) = (n=0 to N-1) _ x(n) exp(-j 2* pi* nk/N) ; k= 0,1,2,N-1

Reverse transforms

X(n) = (1/N) (k=0 to N-1) _ x(k) exp(-j 2* pi* nk/N) ; n= 0,1,2,N-1

3. Write the properties of Hadamard transform

Ans.

1) Hadamard transform contains any one value.

2) No multiplications are required in the transform calculations.4) The no: of additions or subtractions required can be reduced from N^2 to about

Nlog2N

5) Very good energy compaction for highly correlated images.

4. What is Chromatic Adoption?

Ans. The hue of a perceived color depends on the adoption of the viewer. For example, theAmerican Flag will not immediately appear red, white, and blue of the viewer has been subjected

to high intensity red light before viewing the flag. The color of the flag will appear to shift in hue

toward the red component cyan.

5. How the blur is removed caused by uniform linear motion?

Ans. An image f(x,y) undergoes planar motion in the x and y-direction and x0(t) and y0(t) are

the time varying components of motion. The total exposure at any point of the recording medium(digital memory) is obtained by integrating the instantaneous exposure over the time interval

during which the imaging system shutter is open.

6. What is Image Transform?

Ans. An image can be expanded in terms of a discrete set of basis arrays called basis

images. These basis images can be generated by unitary matrices. Alternatively, a

given NXN image can be viewed as an N^2X1 vectors. An image transform provides aset of coordinates or basis vectors for vector space.

7. Name the categories of Image Enhancement and explain?

Ans. The categories of Image Enhancement are

1. Spatial domain2. Frequency domain

8/7/2019 chan viva

26/41

Spatial domain: It refers to the image plane, itself and it is based on direct manipulation of

pixels of an image.

Frequency domain techniques are based on modifying the Fourier transform of an image.

8. What is Huffman Coding?

Ans. Huffman compression reduces the average code length used to represent the symbols of an

alphabet. Symbols of the source alphabet, which occur frequently, are assigned with short lengthcodes. The general strategy is to allow the code length to vary from character to character and to

ensure that the frequently occurring characters have shorter codes.

ANTENNAS AND WAVE PROPAGATION

1. What is meant by radiation pattern?

Ans. Radiation pattern is the relative distribution of radiated power as a function of distance inspace .It is a graph which shows the variation in actual field strength of the EM wave at all points

which are at equal distance from the antenna. The energy radiated in a particular direction by anantenna is measured in terms of FIELD STRENGTH.(E Volts/m)

2. What is meant by antenna beam width?

Ans. Antenna beam width is a measure of directivity of an antenna. Antenna beam width is an

angular width in degrees, measured on the radiation pattern (major lobe) between points wherethe radiated power has fallen to half its maximum value .This is called as beam width between

half power points or half power beam width.(HPBW).

3.What is meant by uniform linear array.?

Ans. An array is linear when the elements of the array are spaced equally along the straight line.

If the elements are fed with currents of equal magnitude and having a uniform progressive phaseshift along the line, then it is called uniform linear array .

4. List the applications of helical antenna?

Ans.The applications of helical antenna are:

It became the workhouse of space communications for telephone,television and data, being employed both on satellites and at ground

stations

Many satellites including weather satellites, data relay satellites all have

helical antennas

8/7/2019 chan viva

27/41

It is on many other probes of planets and comets, including moon andmars, being used alone, in arrays or as feeds for parabolic reflectors, its

circular polarization and high gain and simplicity making it effective for

space application

5. What is meant by Space Wave.?

Ans. It is made up of direct wave and ground reflected wave. Also includes the portion of energy

received as a result of diffraction around the earth surface and the reflection from the upper

atmosphere

6. What is meant by Faraday s rotation?

Ans. Due to the earth s magnetic fields, the ionosphere medium becomes anisotropic and the

incident plane wave entering the ionosphere will split into ordinary and extra ordinary

waves/modes. When these modes re-emerge from the ionosphere they recombine into a singleplane wave again. Finally the plane of polarization will usually have changed, this phenomenon

is known as Faraday s rotation.

7. Define LUHF?

Ans. The lowest useful HF for a given distance and transmitter power is defined as the lowestfrequency that will give satisfactory reception for that distance and power.

It depends on

The effective radiated power

Absorption character of ionosphere for the paths between transmitter and receiver.

The required field strength which in turn depends upon the radio noise at the

receiving location and type of service involved .

8. Define skip distance?

Ans. The distance with in which a signal of given frequency fails to be reflected back is the skip

distance for that frequency. The higher the frequency the greater the skip distance.

MICROWAVE ENGINEERING

1. Define s-matrix

Ans. In a microwave junction there is intersection of three or more components. There will be an

output port ,in addition there may be reflection from the junction of other ports. Totally there

may be many combinations, these are represented easily using a matrix called S matrix

2. What are ferrites and give its properties?

Ans. Ferrites are ceramic like materials. These are made by by sintering a mixture of metallic

oxides.

Properties

Specific resistivity is may be used as much as 1014 greater than that of metals

8/7/2019 chan viva

28/41

Dielectric constants around 10to 15 or greater

Relative permeability is 1000

3.What is Faradays rotation law?

Ans. If a circularly polarized wave is made to pass through a ferrite rod which has been

influenced by an axial magnetic field B ,then the axis of polarization gets tilted in clockwise

direction and amount of tilt depends upon the strength of magnetic field and geometry of theferrite

. What are the assumptions for calculation of RF power in Reflex Klystron?

Ans.

i) Cavity grids and repeller are plane parallel and very large in extent.

ii) No RF field is excited in repeller space

iii) Electrons are not intercepted by the cavity anode grid.iv) No debunching takes place in repeller space.

v) The cavity RF gap voltage amplitude V, is small compared to the dc beamvoltage VO

5. Dicuss the high frequency effects in conventional tubes?

Ans. The high frequency effects in conventional tubes are

i) Circuit reactancea)Inter electrode capacitance

b) Lead inductanceii) Transit time effectiii) Cathode emission

iv) Plate heat dissipation area

v) Power loss due to skin effect, radiation and dielectric loss

6. What is the purpose of slow wave structures used in TWT amplifiers?

Ans. Slow wave structures are special circuits that are used in microwave tubes to reduce wavevelocity in a certain direction so that the electron beam and the signal wave can interact. In

TWT, since the beam can be accelerated only to velocities that are about a fraction of the

velocity of light, slow wave structures are used.

7. What are the applications of TRAPATT devices?

Ans. The applications are

a)Phased-array Radar systemsb)Intermediate frequency transmitters.

8/7/2019 chan viva

29/41

c)Proxity fuse sources

d)Radio altimeters

e)Microwave landing systems.

8.What is negative resistance in gunn diode?

Ans. The carrier drift velocity increases linearly from 0 to maximum when the electric field is

increased from 0 to threshold value in gunn diodes. When the electric field is beyond thethreshold value of 3000v/cm the drift velocity is decreased and the diode exhibit negative

resistance.

OPTICAL COMMUNICATION

1. Define Numerical aperture of a step index fiber?

Ans. Numerical aperture (N.A) of the fiber is the light collecting efficiency of the fiber and is the

measure of the amount of light rays that can be accepted by the fiber. It is equal to the sine ofacceptance.

N.A= n0 sin 0max = (n12 - n2

2)1/2

where n1 and n2 are the refractive indices of core and cladding respectively.

2. What are the uses of optical fibers?

Ans. a) To transmit the information which are in the form of coded signals of the

telephone communication, computer data, etc.b) To transmit the optical images (Example : Endoscopy)

c) To act as a light source at the inaccessible places.d) To act as sensors to do mechanical, electrical and magnetic measurements

3. What is Guide dispersion?

Ans. Wave guide dispersion which occurs because of a single mode fiber confines only about

80% of optical power to the core. Dispersion this arises since 20% of light propagates in

cladding travels faster than the light confined to the core. Amount of wave-guide dispersiondepends on fiber design. Other factor for pulse spreading is inter modal delay

4. Give an account on single mode lasers and modulation of laser diodes.?

Ans. Single mode lasers:

It is used for long-distance communication.

It consists of a single longitudinal mode and single transverse mode.The spectral width is low.

Alternative devices developed are

8/7/2019 chan viva

30/41

1. Vertical cavity surface emitting lasers

2. Structures that have a built-in frequency-selective grating.

3. Tunable lasers.

5. Define direct band gap materials and indirect band gap materials.?

Ans.Direct band gap:In direct band gap materials direct transition is possible from valence band to conduction band.

e.g. GaAs, InP, InGaAs

Indirect band gap:

In indirect band gap materials direct transition is not possible from valence band to conduction.

e.g. silicon, germanium.

6. Define internal quantum efficiency.

Ans. The internal quantum efficiency is the fraction of the electron-hole pairs that recombineradiatively.If the radiative recombination rate is R and the non radiative recombination rate is

Rnr, then the internal quantum efficiency is the ratio of the ratio of the radiative recombinationrate to the total recombination rate

7. What is meant by population inversion?

Ans. In thermal equilibrium, the density of excited electrons is very small. Most photons incident

on the system will therefore be absorbed, so that stimulated emission is essentially negligible.

Stimulated emission will exceed absorption only if the population of the excited states is greaterthan that of the ground state. This condition is known as population inversion.

8. Write in detail about avalanche photodiodes and explain briefly about photo detector

noise and SNR?

Ans.

Avalanche photodiodes

a. Impact ionization

b. Avalanche effect

c. Reach-through constructiond. p+ _ p n+ reach- through structure

e. Principle of reach through

f. Ionization rate

Photo detector noise

SNR at output of an optical receiver

Condition to achieve a high SNRSNR

S = (ip2)M2

N 2q(Ip+ID)M2F(M)+2qILB+4KBTB/RL

8/7/2019 chan viva

31/41

EM WAVES AND TRANSMISSION LINES

1. Define conductivity of a material?

Ans. According to the Ohms laws, conductivity defined as the current density per unit electricfield. Based upon conductivity materials classified into two types,

1. Conductors

2. Non-conductors.Conductivity of the material depends upon the frequency and temperature.

2. Define magnetic flux density?

Ans. Magnetic flux constitutes the magnetic lines of force produced by a permanent magnet or a

current carrying conductor. In case of current carrying conductor, the magnetic lines of forcesurround the conductor to form concentric circles and they do not intersect each other.

3. Explain faraday's law for time varying fields?

Ans. Faraday's first law of electromagnetic induction states that "When ever the number of

magnetic lines of force (called as magnetic flux) passing through a conductor changes, an e.m.f

is induced in it".Faraday's second law of electromagnetic induction states that "The magnetic of the

induced e.m.f. is proportional to the rate of change of magnetic lines of force".

4. What is meant by the polarization of wave?

Ans. By definition, the polarization of a wave is the locus of the tip of the electric field at a given

point as a function of time. When two or more waves of the same frequency propagate in thesame direction.

5. Define plane of incidence?

Ans. If the wave travel through one medium and then enters another medium of infinite extent

and is assumed that the interface between the two media is normal to the direction of propagation

of the incoming wave is called the incident wave and the medium in which this waves travels is

called plane of incidence.

6. Explain the term "conduction current"?

Ans. It is the current caused by the applied electric field to any conductor, A.A current through a

resistive element is called conduction current. If a constant potential difference is applied acrossa conductor produces a continuous flow of current of constant value can be termed as conduction

current.

8/7/2019 chan viva

32/41

7. Define reflection coefficient?

Ans. It is the ratio of reflected to incident electric field strength. Reflection coefficient has

different values for both parallel and perpendicular polarization.

8. What are equi-potential surfaces?

Ans. If the potential throughout the surface is same, then such surface is referred as equi-potential surface. The line intersection of an equi-potential surface and a plane results

in a path or line known as an equi-potential line.

RADAR SYSTEMS

1. Give the Radar equation?

Ans. The powerPr returning to the receiving antenna is given by the radar equation:

2. Write short notes about Noise in Radar?

Ans. Signal noise is an internal source of random variations in the signal, which is generated by

all electronic components. Noise typically appears as random variations superimposed on the

desired echo signal received in the radar receiver.3. What isDoppler effect?

Ans. Ground-based radar systems used for detecting speeds rely on the Doppler effect. The

apparent frequency (f) of the wave changes with the relative position of the target. The Doppler

equation is stated as follows forvobs (the radial speed of the observer) and vs (the radial speed of

the target) and f0 frequency of wave :

4. What is FM CW RADAR?

Ans. Frequency Modulated Continuous-wave radar is a short range measuring radar set. This

kind of radar is often used as radar altimeter to measure the exact height during the landing

procedure of aircraft

8/7/2019 chan viva

33/41

FMCW) is a radarsystem where a known stable frequency wave radio energy is

modulated by a triangular modulation signal so that it varies gradually and then mixes

with the signal reflected from a target object with this transmit signal to produce a beat

signal.

5. What is MTI Radar?

Ans.

MTI radars introduce additional loss. The MTI discrimination technique results in

complete loss of sensitivity for certain target values (blind speeds)

In a radar with overlapping range gates, the gates may be wider than optimum for

practical reasons.

The additional noise introduced by non optimum gate width leads to

degradation performance.

Straddling loss accounts for loss in SNR for targets not at the centre of a range

gate, or at the centre of a filter in a multiple bank processor

6. What is RADAR attrack extraction?

Ans. Radar video returns on aircraft can be subjected to a plot extraction process whereby

spurious and interfering signals are discarded. A sequence of target returns can be monitored

through a device known as a plot extractor. The non relevant real time returns can be removed

from the displayed information and a single plot displayed. In some radar systems, or

alternatively in the command and control system to which the radar is connected, a radar

tracker is used to associate the sequence of plots belonging to individual targets and estimate the

targets' headings and speeds.

7. Reduction of interference effects in Radar?

Ans. Signal processing is employed in radar systems to reduce the radar interference effects.

Signal processing techniques include moving target indication (MTI), pulse Doppler, moving

target detection (MTD) processors, correlation with secondary surveillance radar (SSR)

targets, space-time adaptive processing (STAP), and track-before-detect (TBD). Constant false

alarm rate (CFAR) and digital terrain model (DTM) processing are also used in clutter

environments

8. What are the requirements of Radar receiver?

Ans. The ideal radar receiver is required to:

amplify the received signals without adding noise or introducing any form of distortion;

optimise the probability of detection of the signal by its bandwidth characteristics.

http://en.wikipedia.org/wiki/Radarhttp://en.wikipedia.org/wiki/Radar

8/7/2019 chan viva

34/41

provide a large dynamic range to accommodate large clutter signals;

reject interfering signals so that the required information can be optimally detected.

. ANALOG COMMUNICATIONS

1. What is the need for modulation?

Ans. Mainly to decrease the antenna size

to increase the bandwidth of the signal

to multiplex the signals

to reduce the interference made when we transmit the signals with nearly same

frequency in the audio frequency range (20-20k)kHz.

to favour the complexity of the transmission system

2. What is Costas Loop?

Ans. A Costas loop is a phase-locked loop used for carrier phase recovery from suppressed-

carrier modulation signals, such as from double-sideband suppressed carrier signals. The primary

application of Costas loops is in wireless receivers. Its advantage over the PLL-based detectors is

that at small deviations the Costas loop error voltage is sin(2(if)) vs sin(if). This translates

to double the sensitivity and also makes the Costas loop uniquely suited for tracking Doppler-

shifted carriers esp. in OFDM and GPS.

3. What is SSB?

Ans. Single-sideband modulation (SSB) is a refinement of amplitude modulation that moreefficiently uses electrical power and bandwidth. It is closely related to vestigial sideband

modulation (VSB)

Amplitude modulation produces a modulated output signal that has twice the bandwidth of the

original baseband signal. Single-sideband modulation avoids this bandwidth doubling, and thepower wasted on a carrier, at the cost of somewhat increased device complexity.

4. What is FM?

Ans. Frequency modulation (FM) conveys information over a carrier wave by varying its

instantaneous frequency. This is in contrast with amplitude modulation, in which the amplitude

of the carrier is varied while its frequency remains constant. In analog applications, the

difference between the instantaneous and the base frequency of the carrier is directly

proportional to the instantaneous value of the input signal amplitude. Digital data can be sent by

http://en.wikipedia.org/wiki/GPS_receiverhttp://en.wikipedia.org/wiki/GPS_receiver

8/7/2019 chan viva

35/41

shifting the carrier's frequency among a set of discrete values, a technique known as frequency-

shift keying.

FM is widely used for broadcasting of music and speech, and in two-way radio systems

5. Noise in Analog communication?

Ans. Analog systems are less tolerant to noise, make good use of bandwidth, and are easy to

manipulate mathematically. However, analog signals require hardware receivers and transmitters

that are designed to perfectly fit the particular transmission. If you are working on a new system,

and you decide to change your analog signal, you need to completely change your transmitters

and receivers.

6. What is a Radio transmitter?

Ans. Radio transmitter is an electronic device which, with the aid of an antenna, produces radio

waves. The transmitter itself generates a radio frequency alternating current, which is applied to

the antenna. When excited by this alternating current, the antenna radiates radio waves. In

addition to their use in broadcasting, transmitters are necessary component parts of many

electronic devices that communicate by radio.

7.What is a Radio receiver?

Ans. A radio receiver is an electronic circuit that receives its input from an antenna, uses

electronic filters to separate a wanted radio signal from all other signals picked up by this

antenna, amplifies it to a level suitable for further processing, and finally converts through

demodulation and decoding the signal into a form usable for the consumer, such as sound,

pictures, digital data, measurement values, navigational positions, etc

8. What is TDM?

Ans. Time-division multiplexing (TDM) is a method of putting multiple data streams in a single

signal by separating the signal into many segments, each having a very short duration. Eachindividual data stream is reassembled at the receiving end based on the timing.

The circuit that combines signals at the source (transmitting) end of a communications link is

known as a multiplexer. It accepts the input from each individual end user, breaks each signal

into segments, and assigns the segments to the composite signal in a rotating, repeatingsequence.

8/7/2019 chan viva

36/41

8/7/2019 chan viva

37/41

QPSK is applied extensively on certain systems. It can be used to maintain the data rate while

ensuring that the bandwidth of the signal is stable. This enables the system to efficiently utilize

its bandwidth resources.

4. What is baseband signal?

Ans. A baseband signal converter device for an impulse radio receiver combines multiple

converter circuits and an RF amplifier in a single integrated circuit package. Each converter

circuit includes an integrator circuit that integrates a portion of each RF pulse during a samplingperiod triggered by a timing pulse generator. The integrator capacitor is isolated by a pair of

Schottky diodes connected to a pair of load resistors. A current equalizer circuit equalizes the

current flowing through the load resistors when the integrator is not sampling. Current steeringlogic transfers load current between the diodes and a constant bias circuit depending on whether

a sampling pulse is present.

5. Define Shannons Entropy?

Ans. Shannon's entropy represents an absolute limit on the best possible lossless compression of

any communication, under certain constraints: treating messages to be encoded as a sequence ofindependent and identically-distributed random variables, Shannon's source coding theorem

shows that, in the limit, the average length of the shortest possible representation to encode the

messages in a given alphabet is their entropy divided by the logarithm of the number of symbolsin the target alphabet.

6. Define Shannons Theorem?

Ans. A given communication system has a maximum rate of information C known as thechannel capacity.

If the information rate R is less than C, then one can approach arbitrarily small error

probabilities by using intelligent coding techniques.

To get lower error probabilities, the encoder has to work on longer blocks of signal data.

This entails longer delays and higher computational requirements.

7. What is linear block codes?

Ans. If more error-correcting bits are included with a message, and if those bits can be arranged

such that different incorrect bits produce different error results, then bad bits could be identified.In a 7-bit message, there are seven possible single bit errors, so three error control bits couldpotentially specify not only that an error occurred but also which bit caused the error

8. What is Convolutional Codes?

Ans. This chapter describes the encoder and decoder structures for convolutional codes. Theencoder will be represented in many different but equivalent ways. Also, the main decoding

8/7/2019 chan viva

38/41

strategy for convolutional codes, based on the Viterbi Algorithm, will be described. A firm

understanding of convolutional codes is an important prerequisite to the understanding of turbo

codes.

TELECOMMUNICATION SWITCHING SYSTEMS

1. Principles of cross bar switching?

Ans. A crossbar switch (also known as cross-point switch, crosspoint switch, or matrix

switch) is a switch connecting multiple inputs to multiple outputs in a matrix manner. Originally

the term was used literally, for a matrix switch controlled by a grid of crossing metal bars, and

later was broadened to matrix switches in general. It is one of the principal switch architectures,

together with a memory switch and a crossover switch.

2. What is Electronic space division switching?

Ans. All the automatic telephone switches, both electromechanical and electronic, discussed up

to this point are classified as space-division switches. Space-division switches are characterized

by the fact that the speech path through a telephone switch is continuous throughout the

exchange. That speech path is a metallic circuit, in the sense that it is provided entirely through

the metallic.

3. What is Subscriber loop systems?

Ans. Subscriber Loop Carrier (SLC - commonly pronounced "slick") refers to equipment

providing central office-like telephone interface functionality. The SLC Remote Terminal (RT)is typically located in a remote (from the telephone company central office) area with a high

density of telephone service such as a residential neighborhood.

4. What is Grade of service and blocking probability?

Ans. Grade of service is the probability of a call in a circuit group being blocked or delayed for

more than a specified interval, expressed as a vulgar fraction or decimal fraction. This is always

with reference to the busy hour when the traffic intensity is the greatest. Grade of service may beviewed independently from the perspective of incoming versus outgoing calls, and is not

necessarily equal in each direction or between different source-destination pairs.

5. Define network architecture?

Ans. Network architecture is the design of a communications network. It is a framework for thespecification of a network's physical components and their functional organization and

configuration, its operational principles and procedures, as well as data formats used in its

operation.

8/7/2019 chan viva

39/41

In telecommunication, the specification of a network architecture may also include a detailed

description of products and services delivered via a communications network, as well as detailed

rate and billing structures under which services are compensated.

6. What is OSI model?

Ans. The Open Systems Interconnection model (OSI model) is a product of the Open Systems

Interconnection effort at the International Organization for Standardization. It is a way of sub-

dividing a communications system into smaller parts called layers. A layer is a collection of

similar functions that provide services to the layer above it and receives services from the layer

below it. On each layer, an instance provides services to the instances at the layer above and

requests service from the layer below.

7. What is ISDN?

Ans. Integrated Services Digital Network (ISDN) is a set of communications standards for

simultaneous digital transmission of voice, video, data, and other network services over thetraditional circuits of the public switched telephone network.

8. What is cable modem?

Ans. A cable modem is a type of network bridge and modem that provides bi-directional data

communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems

are primarily used to deliver broadband Internet access in the form of cable Internet, taking

advantage of the high bandwidth of a HFC and RFoG network. They are commonly deployed in

Australia, Europe, Asia and Americas

Hybrid fiber-coaxial (HFC) is a telecommunications industry term for a broadband network

which combines optical fiber and coaxial cable.

Radio Frequency over Glass (RFoG) is a deep fiber network design in which the coax portion of

the HFC network is replaced by a single-fiber, passive optical architecture (PON)

CELLULAR AND MOBILE COMMUNICATIONS

1. What is Cellular network?

Ans. A cellular networkis a radio network distributed over land areas called cells, each served

by at least one fixed-location transceiver known as a cell site or base station. When joined

together these cells provide radio coverage over a wide geographic area. This enables a large

number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each

8/7/2019 chan viva

40/41

other and with fixed transceivers and telephones anywhere in the network, via base stations, even

if some of the transceivers are moving through more than one cell during transmission

2. What are the elements in Cellular Mobile Radio System Design?

Ans. Elements of Cellular Mobile Radio System Design1 (1) the concept of frequency reuse channels

2 (2) the cochannel interference reduction factor

3 (3) the desired carriertointerference ratio

4 (4) the handoff mechanism

5 (5) cell splitting.

3. What is co channel interference?

Ans. Co-channel interference with a desired signal in a receiver arrangement of a TDMA cellular

radio communications system having two antennas and receivers for providing two received

signals is reduced. Two sampled signals are derived from each of the two received signals by

sampling the respective received signal at twice the symbol rate of the system and separating

alternate samples at twice the symbol rate to produce the two sampled signals each with different

samples at the symbol rate, providing a total of four sampled signals from the two antennas.

These signals are linearly combined with respective weights to produce an output signal, the

weights being determined to reduce co-channel interference with the desired signal represented

by the output signal.

4. Discuss the merits of point-to-point model?

Ans. 1.The point-to-point provides a more accurate path loss data, while the area-to-area modelprovides data with 8 bD in case of point-to-point model.

2.The point-to-point prediction model can generate signal coverage maps, interference area

maps, hands-off occurrence maps.

5. What is Omni directional antenna?Ans. An omnidirectional antenna is an antenna which

radiates power uniformly in one plane, with the radiated power decreasing with elevation angle

above or below the plane, dropping to zero on the antenna's axis. Omnidirectional antennas are

widely used for radio broadcasting antennas, and in mobile devices that use radio such as cellphones, FM radios, walkie-talkies, Wifi, cordless phones, GPS as well as for base stations that

communicate with mobile radios, such as police and taxi dispatchers and aircraft

communications.

6. What is Channel allocation?

8/7/2019 chan viva

41/41

Ans. In TDMA and FDMA based cellular radio systems and wireless networks, channel

allocation schemes are required to allocate channels to base stations and access points and to

avoid co-channel interference among nearby cells. A number of approaches have been tried to

assign bandwidth to users in an efficient manner while minimizing interference to other users.

7. What is cell splitting?Ans. Cell splitting is one of the concept used to improve the utilization of spectrum efficiency.

When the traffic density is more in the system then the frequency channel present in a cell unitprovide enough mobile calls, hence the original call be split into smaller cells, which is known as

cell splitting.

8. What are GSM channels?

Ans. GSM provides a number of different types of channels for user traffic and signaling.

These channels are divided into two classes:

1. Traffic channels

2. Signaling channels