Digital Electronics Interview Questions

Introduction to Digital Electronics Interview Questions

Digital electronics is electronics that operate on digital signals where digital electronic circuits are made from a series of logic gates by assembling them. Each logic gate performs a function based on Boolean values with help of signals from logic gates. In general logic gates are created from one or more switches controlled electrically like transistors. Engineers use different methods to use fewer logic functions, to reduce the digital electronic circuit complexity so that it will be less expensive. In general digital circuits are represented using two types of digital systems such as combinational system and a sequential system where combinational system represents same output when it receives same input and a sequential system is described as a combinational system with some of the outputs as inputs i.e. feedback. As digital circuits are made from analog components we need to make sure that analog components behavior should not dominate the digital behavior. There will be so many challenges and issues while designing and representing digital circuits. I will be focusing on mostly asked digital electronics topics in interviews and discussing top ten topics with digital electronics interview questions.

Now, if you are looking for a job which is related to Digital electronics then you need to prepare for the 2019 Digital electronics interview questions. It is true that every interview is different as per the different job profiles. Here, we have prepared the important Digital electronics interview questions and answers which will help you get success in your interview.

In this 2019 Digital electronics interview questions article, we shall present 10 most important and frequently asked Digital electronics interview questions. These Digital electronics interview questions are divided into two parts are as follows:

Part 1 – Digital Electronics Interview Questions (Basic)

This first part covers basic Digital Electronics Interview Questions and Answers.

Q1.What is the difference between Latch and Flip-flop?

Answer:
The difference between latch and flip-flop is that latches are level sensitive while flip-flops are edge sensitive. Both latch and flip-flop will be used in sequential logic and requires a clock signal. Latch output will track the input when the signal is high i.e. when the clock is high 1, the output can change if input changes. Whereas in flip-flop input will be stored only when there is a raising/falling edge of the clock and it is immune to glitches where Latch is sensitive to glitches. Latches need fewer logic gates than flip-flop to implement, so latches are faster than a flip-flop.

Q2.Why did hexadecimal number system call as an alphanumeric number system?

Answer:
The hexadecimal number system is called as alphanumeric number system as hexadecimal number system has a base as 16, so it requires 16 unique symbols to represent the hexadecimal number. These are numbers from 0-9 and alphabets from A to F. As both numbers and alphabets both are used to represent numbers in hexadecimal number system it is called as an alphanumeric number system.

Q3.What is the difference between Mealy and Moore state machines?

Answer:
Moore Machine: This machine is a basic model of a state machine, a state machine whose output depends on the state by using only entry actions is called a Moore model.

Mealy Machine: This machine is a basic model of a state machine, a state machine whose output depends on both input and state is called a Mealy model.

The choice between these models will depend on the type of application, project requirement and complexity. Most of the models will depend only on state whereas Mealy model output depends on both inputs and states.

Let us move to the next Digital Electronics Interview Questions.

Q4.Why most interrupts active Low?

Answer:
The reason for most signals to be active low is as below: If you consider transistor as an example, active low means the capacitor in transistor output terminal will get charged or discharged based on signals from low to high or from high to low transitions respectively. When the signal goes from high to low it depends on the resistor that pulls down it called pull-down resistor. It is easy for output capacitance to discharge rather than charging. So, most people will refer to use signals which are inactive low.

Q5.What is the difference between Sequential and Combinational Circuit?

Answer:
Sequential Circuit: The Sequential circuit is a circuit which will depend on clock cycles, present input and past outputs in-order to generate the output is called Sequential circuit.
Combinational Circuit: The combinational circuit is a circuit which will be called as time-independent circuits i.e. they won’t dependent on time clocks and previous inputs in-order to generate the output is called Combinational circuit.

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Part 2 – Digital Electronics Interview Questions (Advanced)

Let us now have a look at the advanced Digital Electronics Interview Questions.

Q6.What is the race around the problem, how you resolve it?

Answer:
Race around a problem is defined as below in terms of a digital circuit as the time clock pulse will remain in state 1 while both J and K inputs are equal to 1 and it will cause the output to complement and these set of states repeats until the pulse goes back to 0 called race around a problem. In order to avoid this situation, clock pulse needs to have the time duration which is less than propagation delay time for F-F which is restrictive. So the alternative is master-slave or edge triggered construction.

Q7.How will you implement a full subtractor from a full adder?

Answer:
It can be implemented as by connecting all the bits of subtractor to the xor-gate and other input to xor as one and then carry bit as an input to full adder which needs to be made as one. So, Full adder will work as a Full subtractor.

Let us move to the next Digital Electronics Interview Questions.

Q8.Define Minterm and Maxterm?

Answer:

A Minterm is defined as the product of Boolean expression where all possible variables will appear once in complement or un-complement variables is called Minterm.

Maxterm is defined as the sum of Boolean expression where all possible variables will appear once in complement or un-complement variables is called Maxterm.

Q9.What is an edge-triggered flip-flop?

Answer:
The problem of a race around condition can be solved by using an edge-triggered flip-flop. The edge-triggered flip-flop will change its state either at the positive edge or negative edge of the clock pulse. The edge-triggered flip-flop is sensitive to its inputs only at this transaction of a flip-flop.

Q10.What are different types of shift register Counter?

Answer:
There are two types of shift register counters such as Ring counter and Johnson counter.

Ring Counter: Ring Counter is defined as a circular shift register with only one flip-flop being set at any time and other bits will get cleared.

Johnson Counter: Johnson counter is defined as k-bit switch ring counter with 2^K decoding gates to provide outputs for 2^k timing signals.

Conclusion

Finally, it’s an overview of digital electronics interview questions on major topics. I hope you will have good preparation after reading this 2018 digital electronics interview questions article and I will suggest practicing questions on logical gates for Interview preparation.

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