Welcome to our series on NPTEL course assignments! This week, we are thrilled to share the solutions for the Week 0 Assignment of the NPTEL Digital Electronic Circuits course. This is a foundational assignment designed for practice and is not included in the final evaluation. Stay with us until the end to explore the details of this assignment and gain valuable insights.

Also Read: NPTEL Swayam Courses 2025

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NPTEL Digital Electronic Circuits Week 0 Assignment 2025

The Week 0 Assignment for NPTEL Digital Electronics Circuits serves as an introduction to basic concepts. It provides an excellent opportunity for students to familiarize themselves with the type of questions they can expect in subsequent weeks.

Note: This assignment is for practice purposes only and will not contribute to the final score.

Detailed Solutions

Q1. Which of the following is true about a pn-junction diode?

a. It is forward biased when voltage at anode is greater than voltage at cathode.

b. It is forward biased when voltage at cathode is greater than voltage at anode.

c. The resistance across the diode is higher in forward biased condition as compared to that in reverse bias.

d. The resistance offered by the diode remains same for both forward and reverse biased condition.

Answer: [ a ]  

It is forward biased when voltage at anode is greater than voltage at cathode.

Explanation:

• Forward Bias: A pn-junction diode is forward biased when the anode (p-side) is at a higher potential than the cathode (n-side). In this condition, the diode allows current to flow, and its resistance is low.
• Reverse Bias: When the cathode is at a higher potential than the anode, the diode is reverse biased, and it offers very high resistance, blocking the current (except for a small leakage current).
• Option c and d: These are incorrect because the resistance of the diode is lower in forward bias and much higher in reverse bias.

Q2. Consider the following diagram of a pn-junction diode which is made up of silicon.

Which of the following is incorrect?

a. The arrow describes the direction of current flow when diode is forward biased.

b. Holes and electrons constitute majority current carriers in p-side and n-side of a pn- junction diode in forward bias.

c. The depletion region is widened when the diode is forward biased.

d. The voltage drop across the diode is nearly constant when forward biased and is approximately 0.7V.

Answer: [ C ] 

The depletion region is widened when the diode is forward biased.

Explanation:

• a. The arrow describes the direction of current flow when the diode is forward biased:
  This is correct. The arrow in the diode symbol indicates the conventional current flow direction (from p-side to n-side) in forward bias.

• b. Holes and electrons constitute majority current carriers in p-side and n-side of a pn-junction diode in forward bias:
  This is correct. In forward bias, holes are the majority carriers on the p-side, and electrons are the majority carriers on the n-side.

• c. The depletion region is widened when the diode is forward biased:
  This is incorrect. In forward bias, the applied voltage reduces the barrier potential, and the depletion region narrows, allowing current to flow easily.

• d. The voltage drop across the diode is nearly constant when forward biased and is approximately 0.7V:
  This is correct for a silicon diode. The voltage drop across a silicon pn-junction diode in forward bias is typically about 0.7V.

Q3. Which of the following four Io vs. Vo plots represents the characteristics of an ideal diode? 

Answer: [ C ] 

Q4. When transistors are used in digital circuits they usually operate in:

a. active region

b. breakdown region

c. saturation and cutoff regions

d. linear region

Answer: [ C ]  saturation and cutoff regions

Explanation:

• Active region: This is where a transistor operates in analog circuits, amplifying signals. It is not typically used in digital circuits.
• Breakdown region: This region occurs when the voltage across the transistor is too high, leading to the transistor breaking down. This is not typically used in digital circuits.
• Saturation and cutoff regions: These are the regions used in digital circuits. In the saturation region, the transistor is "on," allowing current to flow, while in the cutoff region, the transistor is "off," and no current flows.
• Linear region: This is more relevant to analog circuits where the transistor behaves as a variable resistor.

In digital circuits, transistors are used as switches, and they operate in the saturation (on) and cutoff (off) regions.

Q5. How many combinations of three variables are possible where each variable can take only two values?

a. 4

b. 8

c. 16

d. 32

Answer: [ B ] 8

Here, n=3. The number of combinations is 2^n = 2^3 = 2*2*2 = 8 

6) In the following circuit, the value of voltages Va, Ve at nodes A and B respectively are:

a. Va = 2.5V, Vb = 5V

b. Va = 5V, Vb = 2.5V

c. Va = 2.5V, Vb = 2.5V

d. Va = 5V, Vb = 5V

Answer: [ b ]  Va = 5V, Vb = 2.5V

Q7. In the following figure,

In which of the following states of the diodes will current now theough the restist it during the positive hall of input AC voltage, Consider diodes to be ideal

a. D1=ON, D2=OFF, D3=OFF, D4=ON

b. D1=ON, D2=OFF, D3=OFF, D4=ON

c. D1=ON, D2=OFF, D3=OFF, D4=ON

d. D1=ON, D2=OFF, D3=OFF, D4=ON

Answer: [ c ]  D1=ON, D2=OFF, D3=OFF, D4=ON

Q8. Which of the following is NOT true about an ideal OP-AMP ?

a. It has zero input resistance.

b. It has infinite gain.

c. It is a differential amplifier.

d. It provides DC voltage gain.

Answer: [ a ]  It has zero input resistance

Q9. If log_2(512) = x then what is X ____ ?

a. 6 

b. 7

c. 8

d. 9    

Answer: [ d ]  9

Q10. Which of the following gates are called as the universal gates?

a. AND gate & OR gate

b. NAND gate & NOR gate

c. XNOR gate & XOR gate

d. NAND gate, NOR gate & NOT gate

Answer: [ b ] NAND gate & NOR gate

Q11. The minimum hardware required to realize a full subtractor is

a. One half subtractor and one OR gate

b. Two half subtractors and one OR gate

c. One half subtractor and one AND gate

d. Two half subtractors and one AND gate

Answer: [ b ] Two half subtractors and one OR gate

Q12. Which of the following are the characteristic equations of J-K and S-R Flip flop?

Answer: [ a ] 

Q13. How many 4:1 multiplexer are required to generate 64:1 multiplexer?

a. 20

b. 21

c. 16

d. 17

Answer: [ b ]  21

Q14. Consider the Johnson Counter and the clock timing diagram as shown in the figure below.

Let the initial state of Johnson Counter be 0000. Consider the delay from ip to oip of each flip- flop is negligible compared to clock time period. After, how much time the o/p of the counter will be all one?

a. 13ms

b. 8ms

c. 9ms

d. 7ms

Answer: [ d ] 7ms

Q15. Which of the following ADC circuit has the fastest conversion time?

a. Counter type converter

b. Successive approximation type converter

c. Flash counter

d. Dual slope converter

Answer: [ c ] Flash counter

Q16. Find the output of the circuit shown below

a. ABC'

b. AB' C

c. A' BC

d. ABC

Answer: [ d ]  ABC

Q17. A ripple counter with positive edge triggered flip flop is given below. If present state of the counter is Q0Q1Q2 = 011 then its next state will be ____ ?

a. 001

b. 010

c. 101

d. 100

Answer: [ d ] 100

Conclusion 

We hope these detailed solutions help you understand the concepts better. Stay tuned for upcoming solutions and tips to ace the NPTEL assignments.

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