# Digital Electronics MCQ

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Digital electronics

Digital electronics

Important questions of basic digital electronics

A negative level triggered flip – flop has a NOT gate present between clock input and the input of AND gate. Thus, the negative level triggered flip – flop change its state when the clock is negative.

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Category: Electronics basics

1. When does a negative level triggered flip-flop in Digital Electronics changes its state?

In Digital Circuits, a frequency division of 2n of the pulsed clock signal can be obtained by connecting n flip – flops in cascade. Thus, for 4 flip – flops clock frequency can be divided by 16.

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Category: Electronics basics

2. What frequency division of the pulsed clock signal can be obtained by connecting 4 flip – flops in cascade?

A digital circuit is a circuit that has a signal that must fall into one of two discrete levels. Each level is read as one of two states (on/off, 0/1, true/false, for example). To perform Boolean logic, digital circuits use transistors to generate logic gates.

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Category: Electronics basics

3. Which of the following is correct for Digital Circuits?

A sequential code is a code where each succeeding code is one binary number more than the preceding code. Thus, 8421 is a sequential code. Sequential codes are useful in manipulating mathematical data.

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Category: Electronics basics

4. Which of the following codes is a sequential code?

The negative level triggered the flip – flop in Digital Electronics changes its state when the clock is negative. Thus, a negative level triggered flip – flop has a NOT gate present between clock input and the input of AND gate.

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Category: Electronics basics

5.  What gate is placed between clock input and the input of AND gate to convert a positive level triggered flip – flop to a negative level triggered flip – flop?

TTL circuit uses multi – emitter transistors which have a smaller area. The capacitance can be represented in terms of area and distance between the plates using the expressions C = Aε0/d. As “C” is directly proportional to “A”, a smaller area leads to a lower capacitance.

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Category: Electronics basics

6. What characteristic will a TTL digital circuit possess due to its multi-emitter transistor?

Check sum enables to find double errors and also find the erroneous bits. The parity method can help in finding only single errors within a word as a double error will not change the parity bits.

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Category: Electronics basics

7. Which of these error-detecting codes enables to find double errors in Digital Electronic devices?

When the clock is low, the input given to D will have no effect. This is because the set and reset pins of the NAND gates are kept high. When HIGH value is given to NAND gates the output result will be zero.

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Category: Electronics basics

8. What will be the output from a D flip – flop if the clock is low and D = 0?

A circuit is a closed-loop through which electrons can pass. Electrical energy is provided in the circuit by a source of electricity, such as a battery.

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Category: Electronics basics

9. What is a Circuit?

TTL circuit uses multi – emitter transistors. These transistors have a smaller area. As Capacitance is directly proportional to area, a smaller area leads to a lower capacitance.

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Category: Electronics basics

10. What will a TTL digital circuit possess due to the presence of a multi – emitter transistor?

According to Hamming’s analysis, a minimum distance of 2 is required for single error detection. This Hamming distance represents the number of bits that are changed from one code word to the other.

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Category: Electronics basics

11. What is the minimum distance required for single error detection according to Hamming’s analysis in Digital Electronics?

A clock must be used along with synchronous control inputs to trigger a change in the flip flop. These flip – flops may be edge – triggered or level – triggered. A change should occur only when the clock changes from 0 to 1 or vice versa.

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Category: Electronics basics

12. What must be used along with synchronous control inputs to trigger a change in the flip flop?

A reflexive code is a code where the code for 9 is the complement of code for 0 and so on. A sequential code is a code where each succeeding code is one binary number more than the preceding code. Excess – 3 code satisfies both these properties.

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Category: Electronics basics

13. Which of the following options correctly represent the characteristic of Excess – 3 code?

An enable pin allows to activate and deactivate the multiplexer. When enable pin is 0, the output is obtained while when enable pin is 0, the multiplexer is disabled.

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Category: Electronics basics

14. Which of these pins will allow to activate and deactivate a multiplexer?

The TTL circuit uses multi – emitter transistors with many emitters in the input. Thus, the number of emitters is determined by the fan – in. Fan – in determines the number of inputs the particular gate can handle

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Category: Electronics basics

15. Which of the following majorly determines the number of emitters in a TTL digital circuit?

The parity method can help in finding only single errors within a word. The double errors cannot be found as the parity of the bits does not change. If double errors need to be identified, the check – sum method can be used.

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Category: Electronics basics

16. How many errors can the Digital Electronics parity method can find in a single word?

Bipolar IC’s can be classified as saturated and non – saturated logic families. ECL (Emitter – coupled Logic) and Schottky TTL are said to come under the non – saturated logic family.

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Category: Electronics basics

17. Which of the following options comes under the non – saturated logic family in Digital Electronics?

Ex – NOR gate is a one – bit comparator as the output for the gate is 1 if similar inputs are given to the gate and output is 0 if different inputs are given to the gate.

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Category: Electronics basics

18. Which of the following points is not correct regarding an Ex – NOR gate in Digital Electronics?

The results “X + XY = X” and “X(X + Y) = X” follows the absorption law. The expression given can be written in the form X + XY = X(1 + Y). Any value – added with 1 will give 1 itself. Therefore 1 + Y = 1 and X + XY = X.

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Category: Electronics basics

19. The result “X + XY = X” follows which of these laws?

A single flip flop is a divide – by – two device. The frequency of the output from a JK flip – flop, when J = 1, K = 1, and a clock with pulse waveform is given is half the frequency of clock input.

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Category: Electronics basics

20.  What will be the frequency of the output from a JK flip – flop, when J = 1, K = 1, and a clock with pulse waveform is given?

A reflexive code is the one where the code for 9 is the complement of code for 0, code for 8 is the complement of code for 1, and so on. Thus, 2421 and 5211 are reflexive codes.

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Category: Electronics basics

21. Which of these code pairs correctly represent Digital Electronics reflective codes?

Two 2 input AND gates are placed with a NOR – based S – R latch to convert it to an S – R flip – flop. One AND gate is given R in one input and clock in the other. Similarly the second AND gate is given S in one input and clock in the other.

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Category: Electronics basics

22.  Which gates in Digital Circuits are required to convert a NOR-based SR latch to an SR flip-flop?

A don’t care condition can take 0 or 1 according to the requirement. SOP expressions may consider it to be 1 to increase the number of 1s and POS expressions may consider it to be 0 to increase the number of 0s.

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Category: Electronics basics

23. What value is to be considered for a “don’t care condition”?

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Category: Electronics basics

24. What is a switching function that has more than one output called in Digital Electronics?

According to Hamming’s analysis, a minimum distance of 3 is required for a single error correction. Hamming distance represents the number of bits that change from one code word to the other.

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Category: Electronics basics

25. What minimum distance is required for a single error correction according to Hamming’s analysis in Digital Electronics?

In a K – map if a group of 1s in eight cells are present, it makes an Octet. A group of 1s in two cells is called a Pair and a group of 1s in four cells is a Quad.

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Category: Electronics basics

26. What is the group of 1s present in 8 cells of a K – map called?

In Digital Electronics, 4 cycles of addition and shifting in a 4 – bit multiplier are required to perform multiplication using the shift method. The multiplicand is copied as a partial product when multiplier bit is 1 and multiplicand is 0 when multiplier bit is 0.

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Category: Electronics basics

27. How many cycles of addition and shifting in a 4 – bit multiplier are required to perform multiplication using the shift method?

The input for which the flip flop changes its state when synchronized with the clock is called the synchronous control inputs. For the S – R flip flop, both S and R are synchronous control inputs

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Category: Electronics basics

28. Which of the following options represent the synchronous control inputs in an S – R flip flop?

A 4 x 1 multiplexer has 2 select lines, 4 input lines, and 1 output line. AND gates are required to pass the inputs. Thus 4 AND gates will be used for each input. 3 – input AND gate is used, where 2 inputs come from each of the select lines and 1 input for the data.

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Category: Electronics basics

29. Which of the following options are correct for a 4×1 multiplexer?

Emitter coupled logic or ECL is a Current – Mode logic. While operating in active mode, they help in eliminating the turn – off delay of saturated transistors. ECL family has a higher switching speed and dissipates more power.

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Category: Electronics basics

30. Which of the following options is a Current – Mode logic used in Digital Circuits?

SR, D, and JK flip flops can be used to construct a serial shift register. A T flip – flop gives the output 0 when input 1 is given and gives output 1 when input 0 is given. Thus, it cannot be used as a serial shift register.

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Category: Electronics basics

31. Which of these flip – flops cannot be used to construct a serial shift register?

If the gate output is high in a TTL circuit, the current must be given to the input of the gate being driven. Thus, the output must act as a current source. In a normal TTL circuit, about 40μA of current is drawn from the input from a output that is HIGH.

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Category: Electronics basics

32.  How must the output of a gate in a TTL digital circuit act when it is HIGH?

The input at which the flip flop changes its state when synchronized with the clock is called the synchronous control inputs. For T flip flop T is the synchronous control input.

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Category: Electronics basics

33. In Digital Circuits, which of the following options represent the synchronous control inputs in a T flip flop?

Two 16 x 1 mux will enable to give 32 inputs. The final output can be obtained after passing the output from each 16 x 1 mux through an OR gate. The select lines will help in selecting a particular output.

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Category: Electronics basics

34. Which of the following gives the correct number of multiplexers required to build a 32 x 1 multiplexer?

Inter–Integrated circuits can be represented by IIC or I2C is also called the Merged Transistor Logic. They use n – p – n or p – n – p transistors to form IC’s.

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Category: Electronics basics

35. Which of these options represent the other name of Inter – Integrated logic?

Computers, information appliances, digital cameras, digital televisions, flash memory, key USB memory, mobile phones, hard discs, and computer memory devices are examples of digital electronics. After analog signals have been transformed to digital form, digital signal processing is applied to them.

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Category: Electronics basics

36. Which of the following is an example of a digital Electronic?

If the gate output is Low in a TTL digital circuit, the gate must be capable of sinking current drawn from the input of gates. Thus, the output must act as a current sink.

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Category: Electronics basics

37.  How must the output of a gate act when it is LOW in a TTL circuit?

Propagation delay represents a function of the switching time of a particular transistor or MOSFET. The propagation delay helps in determining the speed of logic circuits.

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Category: Electronics basics

38. Which characteristic of IC in Digital Circuits represents a function of the switching time of a particular transistor?

Four 4 – bit parallel binary adders along with 16 number of 2 – input AND gates will be required to construct a 4 – bit parallel multiplier. The AND gate helps in getting the partial products while the parallel – adder are used to add the partial products.

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Category: Electronics basics

39. How many AND gates are required to construct a 4 – bit parallel multiplier if four 4 – bit parallel binary adders are given?

A Ripple – carry adder is a parallel binary adder in which the addition of more than 1 – bit data can be done simultaneously. The inputs to a parallel circuit can be sent and processed at once unlike series circuits in which inputs are sent one by one.

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Category: Electronics basics

40. Which of the following digital logic circuits can be used to add more than 1 – bit simultaneously?

The MOS logic family uses the MOSFET devices to perform its operation. NAND and NOR are the basic gates that are the building blocks of most digital circuits.

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Category: Electronics basics

41.  What are the basic gates in MOS logic family?

XNOR gate is called coincidence gate and gives 1 if similar inputs are given to the gate and output is 0 if different inputs are given to the gate. XOR gate is called anti – coincidence gate and gives 0 if similar inputs are given to the gate and output is 1 if different inputs are given to the gate.

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Category: Electronics basics

42. Which gate is called the anti – coincidence and coincidence gate respectively?

The output in a combinational circuit depends on the mixture of input signals present at that moment. It is not determined by the past conditions. The output in a synchronous circuit depends on the mixture of input signals present at that moment and also the past conditions.

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Category: Electronics basics

43. What determines the output from the combinational logic circuit in Digital Electronics?

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Category: Electronics basics

44. What is Digital Electronics?

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45.  Which of the following is a type of digital logic circuit?

A group of 1s in 4 cells of a K – map is called Quad. A group of 1s in 2 cells of a K – map is called Pair and a group of 1s in 8 cells of a K – map is called Octet.

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Category: Electronics basics

46. What is the group of 1s in 4 cells of a K – map called?

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Category: Electronics basics

47.  When can one logic gate drive many other logic gates in Digital Electronics?

Four 4 – bit parallel binary adders along with 16 number of 2 – input AND gates will be required to construct a 4 – bit parallel multiplier. The parallel adders are used to add the partial products which are calculated using the AND gates.

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Category: Electronics basics

48. How many 4 – bit parallel binary adders will be required to construct a 4 – bit parallel multiplier?

When the clock is low, the input given to D will have no effect. The set and reset pins of the NAND gates are high. When a NAND gate is given 1 as an input to any of the pins, the output will always be 0.

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Category: Electronics basics

49. What will be the output from a D flip-flop if D = 1 and the clock is low?

Toggle operation in Digital Circuits like J – K flip – flop occurs when J = 1 and K = 1. The output toggles between 0 and 1 continuously. This oscillation between 0 and 1 leads to a race – around condition which can be solved using a Master – slave flip flop.

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Category: Electronics basics

50. What kind of operation occurs in a J – K flip flop when both inputs J and K are equal to 1?

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