ELECTRONICS BRANCH INTERVIEW QUESTIONS
1.What are the differences between voltage and current controlled devices?
Ans-In any (electronic) device controlling parameter is current it is called current controlled
device. eg bipolar transistor- output current is a function of base current.
In any (electronic) device controlling parameter is voltage it is called voltage controlled device.
eg Field effect transistor- output current is a function of gate voltage.
It depends on the inherent physical mechanism which defines the primary (independent)
controlling parameter.
2- What is the difference between Power Amplifier and Voltage Amplifier?
Ans-Power amplifiers basically amplify both current and voltage (p=v*i). Voltage amplifiers
only amplify the voltage.
In power amplifier feedback employed is current feedback and In voltage amplifier voltage
feedback is employed.
3- why the BJT is known as current controlled device and FET is known as voltage controlled
device ?
Ans- 1. In BJT because of the current the output will vary.
2. Where as in FET by means of Voltage the output is varied.
4-What is the difference between DCS & PLC & SCADA ?
Ans-PLC stands for Programmable Logic Controller DCS for Data control System SCADA for
Supervisory Control And Data Acquisition SCADA involves supervision by a user in most cases
the plant controller.Whereas PLC is the means by which he performs the function of
SCADA.DCS on the other hand stand only to control the system and not to log any data in the
process of controlling .DCS controllers are faster than PLCs In DCS controller we can adjust the
scan time DCS are costly more inputs and outputs are there for DCS and SCADA does not
have a dedicated controller. In a DCS system there is SCADA system already in it but for PLC
system addition all SCADA software must be provided.
5-What is the difference between Silicon Controlled Switch (SCS) and Gate Turn-off Switch
(GTO)?
Ans-scs is nothing but it is the silicon controlled switch as an SCR but gate turn off is that in
which one of the turn off method of SCR.
6-What is the difference between emulator and simulator?
Ans-Simulator: A software program impersonating a Hardware. Thus SIMULATING the
scenarios faced in the original hardware.
Emulator: A Hardware (with or without software) impersonating another Hardware. Thus
ELIMINATING the need for the original.
7- What is the difference between Circuit Switching and Packet Switching?
Ans-Circuit switching is the transmission technology that has been used since the first communication networks in the nineteenth century. In circuit switching, a caller must first establish a
connection to a callee before any communication is possible. During the connection
establishment, resources are allocated between the caller and the callee.
packet switching is a more recent technology than circuit switching which addresses a
disadvantage of circuit switching: the need to allocate resources for a circuit, thus incurring link
capacity wastes when no data flows on a circuit. Packet switching introduces the idea of
cutting data on a flow into packets which are transmitted over a network without any
resource being allocated.
8- the number of columns in a state table for a sequential circuit with m flip-flops and n
inputs is.
Ans-Its 2m+2n because.. If there are m flip-flops there should be 2m nodes. If there are n
inputs then each node will have 2n.
Q-Design a digital circuit which has one input two output and one select line input should be
1000khz output should be 500khz and 250Khz
select line either 0 or 1
if 0 select 250khz
if 1 select 500 khz
Ans-Demux is the circuit which satisfies the given requirement if 0 is given to the select line
250 khz o/p is provided else 500 khz o/p is provided.
9- What are digital electronic flip flops, State the different types of flip flop and their uses.
Ans-Digital electronic flip flops are temporary single bit storage devices. Different types of flip
flops are JK f/f RS f/f T F/F D f/f this flip flops are using as storage device delay purpose as
counter for toggled as shift register etc
10- What is the difference between latches and flip flop ?
Ans-Latch e is a bistable circuit which responds to change of logic level as they occur. It has no
external inputs.
Flip flop is a basic element of memory. It stores a single bit. It has a multiple input.
Latches are level sensitive devices where as Flip flops are edge sensitive device so it is said that
latches are level triggered and flip flop is edge triggered.
11-What is the Tri State of a Signal?
Ans-In digital circuit the gate output can be only high or low. In high state the output source
current at a minimum voltage greater than ~2.8V if load(fan out ) is proper. In low state it will
sink current at max output voltage less than ~0.8V.
Some times it is desirable to have a state output both not high or low. with neither sinking or
sourcing (with high output impedance). This is called tristate. Tristate output cannot change
output condition of succeeding logic gates unless tristate is disabled.
12- what is the main difference between 8085 and 8086 processors?
Ans-8085 is a 8 bit microprocessor,having 16-bit address bus.8086 is a 16-bit microprocessor
having 20-bit address bus.
Q- What is a sequential circuit and What is a combinational circuit? Is there any difference
between them? If yes what is it?
Ans-Combinational circuit are those whose output depends only upon the present inputs but
in sequential circuit the output depends upon both present and past inputs. that is the
difference
Combinational circuit does not have any memory in the feedback path but the sequential
circuit has memory in the feedback path.
Ex of SEQ Circuit: Encoder Decoder etc
Ex of Comb Circuit; Flip flop
13. What is the difference between masking and non-masking?
Ans-In 8085 processor TRAP is a non mask-able interrupt.
Whereas RST 7.5 6.5 5.5 intr are mask-able interrupts.
Mask-able means this interrupts can be left without considering during the execution of the
program.
Non mask-able depicts that it has to be taken into account during the execution of the
program
14. What is difference between Fixed-Bias Circuit & Self-Bias Circuit?
Ans-Fixed bias circuits get their bias voltages from independently designed reference voltage
sources (or even something as simple as a voltage divider). Often is the case that the bias may
be left for the end-user to give some control over the operation point of the circuit.
Self biased circuits get their bias voltages from the circuit itself often in the form of a negative
feedback. This is very useful when a circuit is extremely sensitive to bias points and it becomes
impractical to provide external biases that are correct to very high accuracies. This can happen
in high gain amplifiers with very high impedance output nodes such as a common source
amplifier with an active load. The operation of the circuit depends on the bias of the active
load. It would therefore be desirable to sacrifice some of this gain by providing a negative
feedback from the output to the gate of the active load. This way you wont have to bias the
circuit yourself but will lose some of the gain of the circuit as a price.
15. What is meant by filter? What are the different types of filters?
Ans-Filters are the components of a circuit which remove distortion or ripples.Types of filters :
1. High pass filters
2. Low pass filters
3. Band pass filters
16. what is meant by virtual ground in the op amp ?
Ans-Ideally the output of op-amp should be zero. So for this to happen the 2 inputs must be
same. Hence one of the input is considered to be low or at ground potential. But this input is
not actually ground hence it is called as virtual ground.
17. What is meant by saying at what current is transistor biased?
Ans-Bias current of a transistor is the pre-set DC current when no input voltage signal is applied
to it.
18. What is Race Around Condition in a JK Flip Flop?
Ans-IN J-K FF , The clock time is higher than the output toggling time then for J=1 & K=1 , the
output will be changed irrelevant of our input. This condition is known as "RACE AROUND
CONDITION"..
19. How to Convert Binary to Excess 3 Code and vice versa?
Ans-A number i binary can be converted to excess-3 just by adding the binary equivalent of 3
to the binary number.similarly a number in excess-3 can be converted to binary just by
subtracting the binary equivaent of 3 from the binary number.
20. How to convert Binary to Gray Code?
Ans-Take XOR of binary no. starting from right with the next bit. Add 0 as leftmost bit to get
answer eg. Â 111=7
Gray code 0 XOR 1,1 XOR 1, 1 XOR 1 i.e. 100 ans.
21. What is the meaning of Tristate Signal in Electronics?
Ans-Tristate device is 3 terminal device & it has three states. They are logic 0 logic 1 & high
impedance state or tristate. This device can be used as switch. For ON logic 0 or logic 1
(depending on active low or active high appl) OFF as high independence state.
22. When a sample of germanium and silicon having same impurity density are kept at room
temperature then Resistivity of silicon will be higher than that of germanium, Why?
Ans-The answer is simple. Consider the PN diode for Ge 0.3eV is the breakdown voltage and
in the case of Si its 0.7eV since the impurities are added in the same amount the bond due to
the other atoms of the Si makes it resistive compared to the Ge.. thats all!.
23. Why gold is added to the p-n junction?
Ans-To reflect heat. To reduce the recombination time.
24. Why are the 2 input terminals of an op-amp are called as inverting & non-inverting
terminals?
Ans-Because if we give input to one input means that will produce the same phase output
where as the other(Inverting) pin produce 180 degree phase shifted output.
25. What is the equivalent of negative logic AND gate?
Ans-Negative logic of AND gate is NAND.
26. What are the main advantages of synchronous circuit?
Ans-All the inputs are feed at the rising or falling end of the clock signal. This makes the circuit
to perform task in sync. so that the functional integrity of the logic device is as expected.
27. How does a Signal differ from a Wave?
Ans-Signal means information. Wave is something that carries the information from source to
destination.
28. Why do we use two ground pins in the pin diagram of 8086?
Ans-There are basically two reasons for doing so one is to remove GROUND BOUNCE one
more reason is circuit complexity demands a large amount of current flowing through the
circuits and multiple grounds help in dissipating the accumulated heat so that device will be
safe.
29. What is the difference between Power Amplifier and Voltage Amplifier?
Ans-Power amplifiers basically amplify both current and voltage (p=v*i).
Voltage amplifiers only amplify the voltage.
30. How to manufacture the CMOS inverter?
Ans-It can be made by using pmos and cmos in series. Both gate are connected together and
act as input. Source of pmos is connected to supply. drain of pmos is connected to drain of
nmosand it serves as output. source of nmos is grounded.
31. What are the advantages of using C band for satellite communication?
Ans-Its frequency ranges from 12 to 18MHz.
32. What is a BCD? What are its advantages and disadvantages? Why is an excess-3 code is
called an unweighted code?
Ans-BCD means Binary coded decimal its advantage is it can represent decimal numbers in
the form of binary value says (0000-0 to 1001-9).
Binary codes are divided into weighted binary code and non weighted binary code Excess 3
code is an example of non weighted codes since the position of each bits in excess 3 code does
not have weights says like ones tens hundred in decimal and 2^0 2^1 2^2 in binary.
33. What is power electronics?
Ans- Power electronics is the technology associated with high power which is more than 430v 3
phase supply.Generally it is consider in industries for the efficient conversion control and
conditioning of electric power by static means from its available input form into the desired
electrical output form.
34. What are the differences between microprocessor and micro controller.
Ans-The microprocessor is the integration of a number of useful functions into a single IC
package.
These functions are: The ability to execute a stored set of instructions to carry out user defined
tasks. The ability to be able to access external memory chips to both read and write data from
and to the memory.
Basically a micro controller is a device which integrates a number of the components of a
microprocessor system onto a single microchip.
So a micro controller combines onto the same microchip : The CPU core Memory (both ROM
and RAM) Some parallel digital I/O Essentially a micro controller is obtained by integrating the
key components of microprocessor RAM ROM and Digital I/O onto the same chip die. Modern
micro controllers also contain a wealth of other modules such as Serial I/O Timers and Analogue
to Digital Converters.
35. What is function of ALE in 8085 microprocessor?
Ans-AlE stands for the address latch enableit 's working is that it differentiate the address and
data bus in microprocessor.when it is high it select address bus .when it is low it select data bus.
36. Why we are using the bridge rectifier in most of the circuits instead of full wave rectifier
eventhough the output of both are same?
Ans-In bridge type (FWR) rectifiers center tapping transformer are not required so small
transformers are used and we will get twice of the out put voltage that of the center tapped
FWR.
37. What type of architecture is used in 8085 microprocessor?
Ans- INTEL 8085 is a 8-bit microprocessor.
It's based on Von-Neumann architecture in which the data and instructions are in the same
memory space without any distinction between them.
Data line: 8-bits--Can process 8-bits of data at a time.
Address line: 16-bits--Can address upto 2^16(64KB) of address space.
38. What is Edison Effect?
Ans-Edison Effect is also refferred as "Thermionic emission". Here the charge carriers flow from
a charge-carrying surface due to vibrations caused by thermal energy.
This phenomenon can be seen in the house-hold electrical bulb in which is a metal filament is
heated by the thermal energy from electricity.
39. how to design a software IC using VHDL ?
Ans-you can use software like altera write the required programme download to the chip
here is your software ic.
40. What are semiconductor devices ?
Ans-Semiconductor Devices is nothing but a device which conduct semi /partially conducting (
semiconductor which conduction property lies between conductor and insulator)is termed as
semiconductor device.
41. Why the input resistance of an ideal OP-AMP is infinite and output resistance is zero?
secondly, how can we measure these resistances(input and output) in case of an ideal OP-AMP and
Real OP-AMP in the following conditions when
1- load is not connected.
2- load is connected.
Ans- Ideal OP-AMP is a power full concept.
If one goes through the history of amplifying devices it becomes clear that less it loads the
previous stage better the output signal. ie. it is a trend toward higher and higher input
impedances.
Also it is better to maintain the signal level irrespective of the LOAD connected at the output.
Lesser the output impedance less the signal amplitude reduction when load is connected. ie. it
is a trend toward lower and lower output impedances.
As ideal op-amp is a concept by virtue it has zero output impedance and infinite input
impedance and they are not physically measurable but has to be taken for granted for the
use in theoretical analysis.
To measure input resistance of non ideal op-amp connect a known source at the input and
give a signal (within Specifications) through a current meter of sufficient precision. Input
voltage by current gives the input impedance.
To measure input resistance of non ideal op-amp connect a known source at the input and
give a signal (within Specifications) through a current meter of sufficient precision. Input
voltage by current gives the input impedance.
To measure output resistance of non ideal op-amp connect a known source at the input such
that the output does not saturate and connect a load (within Specifications ) through a
current meter of sufficient precision and measure the output voltage. Output voltage by
current gives the output impedance.
Please refer application notes by device manufacturers freely available in internet for more
precise and practical solutions.
previous stage better the output signal. ie. it is a trend toward higher and higher input
impedances.
Also it is better to maintain the signal level irrespective of the LOAD connected at the output.
Lesser the output impedance less the signal amplitude reduction when load is connected. ie. it
is a trend toward lower and lower output impedances.
As ideal op-amp is a concept by virtue it has zero output impedance and infinite input
impedance and they are not physically measurable but has to be taken for granted for the
use in theoretical analysis.
To measure input resistance of non ideal op-amp connect a known source at the input and
give a signal (within Specifications) through a current meter of sufficient precision. Input
voltage by current gives the input impedance.
To measure input resistance of non ideal op-amp connect a known source at the input and
give a signal (within Specifications) through a current meter of sufficient precision. Input
voltage by current gives the input impedance.
To measure output resistance of non ideal op-amp connect a known source at the input such
that the output does not saturate and connect a load (within Specifications ) through a
current meter of sufficient precision and measure the output voltage. Output voltage by
current gives the output impedance.
Please refer application notes by device manufacturers freely available in internet for more
precise and practical solutions.
42. What is Pulse Width Modulation?
Ans-Pulse width modulation is a modulation technique in which the width of the pulse is
varied in accordance with the message signal. Pulse width Modulation is abbreviated as PWM.
PWM can be used to reduce the total amount of power delivered to a load without losses
normally incurred when a power source is limited by resistive means. This is because the
average power delivered is proportional to the modulation duty cycle. With a sufficiently high
modulation rate, passive electronic filters can be used to smooth the pulse train and recover
an average analog waveform.
PWM is used in sound synthesis circuits.
43. How many type of resistor are there in diode?
Ans-They are two types one is forward resistance
1.Forward resistance
2.Reverse resistance
1.Forward resistance-This is the resistance offered in forward bias condition of the diode. It is
calculated by with the help of graph for voltage and current characteristic.
2.Reverse resistance-This resistance is offered in the reverse bias condition of the diode. It is also
calculated by the same method.
44. Why the shape of OP-AMP is triangular not other shape?
Ans-The Triangular shape symbolizes that it works for continuous signals and hence forth it is an
analog device. ex: Op amp
If it is square then it is digital device. ex: Multiplexer
If the shape is both triangular and square then it is mixed signal device. ex: ADC DAC.
45 What is Interfacing?
Ans-The peripheral (simple input/output devices ) connected with computer to perform tasks
is known as interfacing.
46 How microprocessor works without internal memory?
Ans-microprocessor works without internal memory because it consists of address data and
control buses with some registers to process the task given to processor through the external
memory.
47. What is a sequential circuit and What is a combinational circuit?Is there any difference
between them? If yes what is it?
Ans-Combinational circuit are those whose output depends only upon the present inputs but
in sequential circuit the output depends upon both present and past inputs. that is the
difference.
48. What are digital electronic flip flops, State the different types of flip flop and their uses.
Ans-digital electronic flip flops are temporary single bit storage devices.different types of flip
flops are JK f/f RS f/f T F/F D f/f this flip flops are using as storage device delay purpose as
counter for toggled as shift register etc.
49. What CMOS Transistor?
Ans-CMOS-->>Complementary Metal Oxide Semiconductor
Complementary metal–oxide–semiconductor (CMOS) is a major class of integrated circuits.
CMOS technology is used in chips such as microprocessors micro controllers static RAM and other
digital logic circuits. CMOS technology is also used for a wide variety of analogcircuits such as
image sensors data converters and highly integrated transceivers for many types of
communication.
CMOS is also sometimes explained as complementary-symmetry metal–oxide–semiconductor.
The words "complementary-symmetry" refer to the fact that the typical digital design style
with CMOS uses complementary and symmetrical pairs of p-type and n-type MOSFETs for
logic functions.
Two important characteristics of CMOS devices are high noise immunity and low static power
supply drain. Significant power is only drawn when its transistors are switching between on and
off states; consequently CMOS devices do not produce as much heat as other forms of logic
such as TTL (transistor-transistor logic). CMOS also allows a high density of logic functions on a
chip.
The triple compound "metal–oxide–semiconductor" is a reference to the nature of the physical
structure of early (and interestingly now the very latest) field-effect transistors having a metal
gate electrode placed on top of an oxide insulator which in turn is on top of a semiconductor
material. Instead of metal current gate electrodes (including those up to the 65 nanometre
technology node) are almost always made from a different material poly silicon but the terms
MOS and CMOS nevertheless continue to be used for the modern descendants of the original
process. (See also MOSFET.) Metal gates have made a comeback with the advent of high-k
dielectric materials in the CMOS transistor as announced by IBM and Intel for the 45
nanometre node and beyond.
CMOS technology is used in chips such as microprocessors micro controllers static RAM and other
digital logic circuits. CMOS technology is also used for a wide variety of analogcircuits such as
image sensors data converters and highly integrated transceivers for many types of
communication.
CMOS is also sometimes explained as complementary-symmetry metal–oxide–semiconductor.
The words "complementary-symmetry" refer to the fact that the typical digital design style
with CMOS uses complementary and symmetrical pairs of p-type and n-type MOSFETs for
logic functions.
Two important characteristics of CMOS devices are high noise immunity and low static power
supply drain. Significant power is only drawn when its transistors are switching between on and
off states; consequently CMOS devices do not produce as much heat as other forms of logic
such as TTL (transistor-transistor logic). CMOS also allows a high density of logic functions on a
chip.
The triple compound "metal–oxide–semiconductor" is a reference to the nature of the physical
structure of early (and interestingly now the very latest) field-effect transistors having a metal
gate electrode placed on top of an oxide insulator which in turn is on top of a semiconductor
material. Instead of metal current gate electrodes (including those up to the 65 nanometre
technology node) are almost always made from a different material poly silicon but the terms
MOS and CMOS nevertheless continue to be used for the modern descendants of the original
process. (See also MOSFET.) Metal gates have made a comeback with the advent of high-k
dielectric materials in the CMOS transistor as announced by IBM and Intel for the 45
nanometre node and beyond.
50 . What is Virtual Grounding?
Ans-Virtual grounding is the shorting of the inverting and the non-inverting terminals of the
op-amp.
The i/p resistance of opamp is v high. thus the base currents are v less approx 0. thus no
current flows thru i/p resistance. thus we can say that both the NI and INV terminals of opamp
are virtually shorted. i.e the voltage across both terminals is same. thus if NOW one terminal is
grounded due to virtual short other terminal also will be grounded.
51. Why the input impedance of OP-Amp is so high?
Ans-In OPAMP we have 4 stages 1st stage i.e the input stage is a dual i/p balanced o/p opamp
whose i/p resistance is v high. and if we use FET in case of BJT for 1st stage diffamp then i/p
resistance will be v high in M ohms.
52. what is meant by virtual ground in the op amp ?
Ans-The op amp connected in a negative feedback configuration that is the o/p connected to
the inverting terminal tried to produce the same voltage at the inverting node as we applied
to the non-inverting terminal no matter whatever be the o/p. This happens because the
opamp has a very high differential gain. so only way to not to clip or saturate the o/p in either
positive or negative side is to make their both i/ps at the same potential. so when you apply
the i/p to the inverting terminal and you connect the feedback to the inverting node and your
non-inverting terminal is grounded then op amp tries to force the inverting node at the
ground potential and whatever the difference between these two nodes are amplified.
53. Which one is faster between NAND-SR FF and NOR-SR FF?
Ans-well both deals with same principle.but i think NAND-SR FF is faster than NOR-SR FF
54. Cost of storing a bit is minimum in
1. Cache 2. Register
3. RAM 4. Magnetic tape
Ans-Magnetic Tape
56. How many characters per sec (7 bits + 1 parity ) can be transmitted over a 2400 bps line
if the transfer is synchronous (1 start and 1 stop bit)?
1. 300 2. 240
3. 250 4. 275
Ans- 2400/(7+1+2) 240
57. What does CE mean..U will see it on almost every chip(IC)..
Ans-The CE mark is a mandatory European marking for certain product groups to indicate
conformity with the essential health and safety requirements set out in European Directives.
The letters 'CE' are an abbreviation of Conformité Européenne,
French for European conformity. The CE mark must be affixed to a product if it falls under the
scope of the approx. 20 so called 'New Approach' Directives. Without the CE marking, and
thus without complying with the provisions of the Directives, the product may not be placed in
the market or put into service in the fifteen member states of the European Union and
Norway, Iceland and Liechtenstein. However, if the product meets the provisions of the
applicable European Directives, and the CE mark is affixed to a product, these countries may
not prohibit, restrict or impede the placing in the market or putting into service of the product.
Thus, CE marking can be regarded as the products trade passport for Europe. The CE mark is
not a quality-mark. First, it refers to the safety rather than to the quality of a product. Second,
most quality markings are voluntary opposite to the CE marking, which is mandatory for the
products it applies to. CE indicates conformity with mandatory European safety requirements.
European conformity is certified by following clear and understandable procedures, the so called
‘conformity assessment procedures’.
58. What is the difference between PLC and DCS?
Ans-PLC means Programmable Logic Controller, which can be used to control one particular
control system such as a boiler or a injection system.
but DCS is Distributed control system, which is used to monitor and control the total process
plant. in DCS we have no of controllers connected to a single monitoring system.
59. why the feeding frequency to a microprocessor s twice the operating frequency.
Ans-since 8085 microprocessor operating frequency 5 mega hz but operating frequency is 10
mega hz because crystal effect in processor
60. Do we have any negative frequency?
Ans-no it can't be negative because frequency is simply the reciprocal of time and time can't
be negative.
We use negative frequencies in our calculations just for easiness but remember at last we
neglect it also
61. what is angle and amplitude modulation? what is noise in modulation?
Ans- modulation means change. to send a message of low frequency to a far distance we use
a carrier of high frequency to carry the message. while transferring we change some
parameters of carriers for faithful transformation of message signal. if the amplitude of the
carrier is varied in accordance with frequency of message signal then it is called amplitude
modulation. if either phase or frequency is changed in accordance with the frequency of
message signal then it is called angle modulation.
noise is an unwanted signal which enter in signal while transferring a signal and makes the
signal distorted.
62. what is selective flooding?
Ans- Selective Flooding is a method to compute the QoS of the system
63. what is fixed bias with and without decoupling capacitor
Ans- with ta decoupling capacitor you cannot get output because it blocks the DC and allows only AC OK.... is you do not us it it give the output but it's DC only so no use to have a DC voltage in O/P.
64. what is the main application of SCR in electronic field as well as in software field?
Ans- SCR is a rectifier we use this in power handling applications .
By varying on time and off time of the SCR i.e by giving the pulse to its gate we can vary the
average output power from the main power supply to the required device .
software part
we can use micro controller and write a programme so that to generate required pulses to
control the SCR.
65. What is Biasing?
Ans- Biasing is process of applying potential across any electronic equipment in order to make
it operate as we require.
