## Signals and Systems Interview Questions & Answers

1. Question 1. Define Continuous-time Signal?

A continuous-time signal is a quantity of interest that depends on an independent variable, where we usually think of the independent variable as time. Two examples are the voltage at a particular node in an electrical circuit and the room temperature at a particular spot, both as functions of time.

2. Question 2. Define Signal?

In electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another. The simplest form of signal is a direct current (DC).

4. Question 3. What Are The Major Classifications Of The Signal?

1. Discrete signal
2. continuous signal
3. Non continuous signal
4. periodic signal
5. Non periodic signal.
5. Question 4. State Properties Of Convolution?

1. commutative
2. associative
3. distributive
4. shifting property etc.
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7. Question 5. What Is Dft ?

DFT stands for discrete fourier transform. it converts a finite list of equally spaced samples of a function into the list of coefficients of a finite combination of complex sinusoidal.

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9. Question 6. What Are The Applications Of Correlation?

correlation is used in radar,sonar,digital communication geology etc.

It is of two types:

• cross correlation
• auto correlation
10. Question 7. What Are The Classification Of Continuous Time Signals? Name Them?

1. deterministic and non deterministic signal.

2. periodic and non periodic signal

3. even and odd signal

4. energy and power signal

5. causal and non causal signal

11. Question 8. Give Some Examples Of Causal Signal?

A signal is said to be causal,if it is defined for t>=0. examples are: step signal,unit step signal,exponential signal.

12. Question 9. What Is Amplitude Scaling And Time Scaling?

The amplitude scaling is performed by multiplying the amplitude of the signal by constant. similarly time  scaling is performed by multiplying the variable time by constant.

13. Question 10. What Is Unit Delay Element ?

The unit delay element delay the input signal passing through it by one sample.

y(n)=x(n-1)

14. Question 11. Classify Discrete Time Signal?

1. static and dynamic system
2. causal and non causal system
3. time invariant and time variant signal
4. linear and non linear signal
5. stable and unstable signal.
15. Question 12. State Superposition Theorem?

The response of the system to a weighted sum of signals will be equal to the corresponding weighted sum of the response i.e. output of the system to each of the individual system.” otherwise system will be non linear.

17. Question 13. How The Analog To Digital Conversion Takes Place. Name All The Steps Involved?

A/D conversion takes place in three steps:

• sampling
• quantization
• coding
18. Question 14. What Is Meant By Step Response Of The Dt System?

The output of the system y(n) is obtained for the unit step input u(n) then it is said to be step response of the system.

19. Question 15. Define Transfer Function Of The Dt System?

The Transfer function of DT system is defined as the ratio of Z transform of the system output to the input. That is , H(z)=Y(z)/X(z).

20. Question 16. Define Impulse Response Of A Dt System?

The impulse response is the output produced by DT system when unit impulse is applied at the input.The impulse response is denoted by h(n). The impulse response h(n) is obtained by taking inverse Z transform from the transfer function H(z)

21. Question 17. State The Significance Of Difference Equations?

The input and output behaviour of the DT system can be characterized with the help of linear constant coefficient difference equations.

22. Question 18. Write The Difference Equation For Discrete Time System?

The general form of constant coefficient difference equation is, Here n is the order of difference equation. x(n) is the input and y(n) is the output

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24. Question 19. What Are The Blocks Used For Block Diagram Representation?

The block diagrams are implemented with the help of signal multipliers, adders, delay elements, time advance elements and constant multipliers.

25. Question 20. State The Significance Of Block Diagram Representation?

The LTI systems are represented with the help of block diagrams. The block diagrams are more effective way of system description. Block Diagrams indicate how individual calculations are performed. Various blocks are used for block diagram representation.

26. Question 21. What Are The Properties Of Convolution?

• Commutative
• Associative
• Distributive
27. Question 22. State The Commutative Properties Of Convolution?

Commutative property of Convolution is, x(n)*h(n) = h(n)*x(n)

28. Question 23. State The Associative Properties Of Convolution?

Associative Property of convolution is, [x(n)*h1n)]*h2(n)=x(n)*[h1(n)*h2(n)]

29. Question 24. Define Causal Lti Dt System?

For a LTI system to be causal if h(n)=0, for n<0.

30. Question 25. How The Discrete Time System Is Represented?

The DT system is represented either Block diagram representation of difference equation representation.

31. Question 26. What Are The Classification Of The System Based On Unit Sample Response?

• FIR (Finite impulse Response) system.
• IIR ( Infinite Impulse Response) system.
32. Question 27. What Is Meant By Fir System?

If the system have finite duration impulse response then the system is said to be FIR system.

33. Question 28. What Is Meant By Iir System?

If the system have infinite duration impulse response then the system is said to be FIR system.

34. Question 29. What Is Recursive System?

If the present output is dependent upon the present and past value of input then the system is said to be recursive system.

35. Question 30. What Is Non Recursive System?

If the present output is dependent upon the present and past value of input and past value of output then the system is said to be non-recursive system.

36. Question 31. What Is The Difference Between Recursive And Non Recursive System?

A recursive system have the feed back and the non recursive system have no feed back.And also the need of memory requirement for the recursive system is less than non recursive system.

37. Question 32. Define Realization Structure?

The block diagram representation of a difference equation is called realization structure.These diagram indicate the manner in which the computations are performed.

38. Question 33. What Are The Different Types Of Structure Realization?

• Direct form I
• Direct form II
• Parallel Form.
39. Question 34. What Is Natural Response?

This is output produced by the system only due to initial conditions . Input is zero for natural response. Hence it is also called zero input Response.

40. Question 35. What Is Zero Input Response?

This is output produced by the system only due to initial conditions. Input is zero for zero input response.

41. Question 36. What Is Forced Response?

This is the output produced by the system only due to input. Initial conditions are considered zero for forced response.It is denoted by y (f ) (n).

42. Question 37. What Is Complete Response?

The complete response of the system is equal to the sum of natural response and forced response .Thus initial conditions as well as input both are considered for complete response.

43. Question 38. What Are The Steps Involved In Calculating Convolution Sum?

The steps involved in calculating sum are:

1. Folding
2. Shifting
3. Multiplication
4. Summation