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 bilpolar 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 ControllerDCS for Data control SystemSCADA 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 datain 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  ystem already in it but for PLC sydtem 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 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 500khz

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

9- What are digital elctronic 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-Latche 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  Flipflops 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 ciruit the gate output can be only high or low. In highstate 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 succeding 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; Flipflop

13.    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

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 dependson 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 preset DC current when no input voltage signal is applied to it.

18.    What is Race Around Condition in a JK FlipFlop?

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 irrelavent 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.