Electronics and Telecommunication Technical Questions with Answers

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. E.g. bipolar transistor- output current is a function of base current.In any (electronic) device controlling parameter is voltage it is called voltage controlled device. E.g. Field effect transistoroutput 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.

  • Ø SCADA involves supervision by a user, in most cases the plant controller.
  • Ø Whereas PLC is the means by which he performs the function of SCADA.
  • Ø DCS on the other hand stand only to control the system and not to log any data in the process of controlling.
  • Ø DCS controllers are faster than PLCs, in DCS controller we can adjust the scan time.
  • Ø 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 turnoff method of SCR.

    6. What is the difference between emulator and simulator?
    Ans-Simulator: A software program impersonating 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.

9. 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 1if 0 select 250khz

if 1 select 500khz

Ans-demux is the circuit which satisfies the given requirement if 0 is given to the select line 250khz o/p is provided else 500khz o/p is provided.

10- 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.

11- What is the difference between latches and flip flop?
Ans-Latch 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 whereas Flip-flops are edge sensitive device so it is said that latches are level triggered and flip flop is edge triggered.

12-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.Sometimes 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.

13- What is the main difference between 8085 and 8086 processors?
Ans-8085 is an 8 bit microprocessor, having 16-bit address bus.8086 is a 16-bit microprocessor having 20-bit address bus.

13. 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

14. What is the difference between masking and non-masking?

Ans-In 8085 processor TRAP is a non maskable interrupt.
Whereas RST 7.5, 6.5, 5.5, intr are maskable interrupts.
Maskable means this interrupts can be left without considering during the execution of the program.
Non maskable depicts that it has to be taken into account during the execution of the program

15. 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 won’t have to bias the circuit yourself but will lose some of the gain of the circuit as a price.

16. 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

17. 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.

18. What is meant by saying at what current is transistor biased?
Ans-Bias current of a transistor is the preset DC current when no input voltage signal is applied to it.

19. 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”..

20. 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 equivalent of 3 from the binary number.

21. 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.

22. What is the meaning of Tristate Signal in Electronics?
Ans-Tristate device is 3 terminal devices & 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.

23. 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.

24. Why gold is added to the p-n junction?
Ans-To reflect heat. To reduce the recombination time.

25. 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 whereas the other(Inverting) pin produce 180 degree phase shifted output.

26. What is the equivalent of negative logic AND gate?

Ans-Negative logic of AND gate is NAND.

27. 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.

28. How does a Signal differ from a Wave?
Ans-Signal means information. Wave is something that carries the information from source to destination.

29. 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

30. 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.

31. 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
nmos and it serves as output. Source of nmos is grounded.

32. What are the advantages of using C band for satellite communication?
Ans-Its frequency ranges from 12 to 18MHz

33. What is a BCD? What are its advantages and disadvantages? Why an excess-3 code is called an unweight 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.

34. 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.

35. 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 writes data from and to the memory.
Basically a microcontroller is a device which integrates a number of the components of a microprocessor system onto a single microchip.
So a microcontroller combines onto the same microchip: The CPU core Memory (both ROM and RAM) Some parallel digital I/O Essentially a microcontroller is obtained by integrating the key components of microprocessor RAM ROM and Digital I/O onto the same chip die. Modern microcontrollers also contain a wealth of other modules such as Serial I/O Timers and Analogue to Digital Converters.

36. What is function of ALE in 8085 microprocessor?
Ans-AlE stands for the address latch enable its 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.

37. Why we are using the bridge rectifier in most of the circuits instead of full wave rectifier even though the output of both is same?
Ans-In bridge type (FWR) rectifiers centre tapping transformer are not required so small transformers are used and we will get twice of the output voltage that of the centre tapped FWR.

38. 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 up to 2^16(64KB) of address space.

39. What is Edison Effect?
Ans-Edison Effect is also referred 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.

40. 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

41. 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.

42. 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 OPAMPand
Real OP-AMP in the following conditions when
1- load is not connected.
2- load is connected.

Ans- Ideal OP-AMP is a power ful 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 opamp 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 theoritical analysis.
To measure input resistance of non ideal opamp 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 opamp 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 opamp 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 meaure the output voltage. Output voltage by current gives the output impedance.
Can refer application notes by device manufacturer available in internet for more precise and practical solutions.

43. 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.

44. 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.

45. Why the shape of OP-AMP is triangular no other shape?
Ans-The Triangular shape symbolizes that it works for continuous signals and hence forth it is an analog device. ex: Opamp
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

46. What is interfacing?
Ans-The peripheral (simple input/output devices) connected with computer to perform tasks is known as interfacing.

47 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.

48. 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.

49. 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.

50. 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, microcontrollers, static RAM and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits 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 nanometer technology node) are almost always made from a different material polysilicon 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 nanometer node and beyond