### Model question paper  DIGITAL ELECTRONICS  electronics enginnering diploma 3rd semester

(ii) Model question paper

Course Title : DIGITAL ELECTRONICS
Course Code : 15EC32T Time : 3 Hrs
Semester : Third Max. Marks: 100
Instructions : 1. Answer any SIX question from Part A (5x6=30 Marks)
2. Answer any SEVEN full questions from Part B (7x10=70 Marks)

Part A
1. Define combinational and sequential digital circuits with examples.
2. Describe the functioning of RS flip-flop with gate-level circuit and truth table.
3. Define shift register and list different types of data movements in it.
4. Sketch the timing diagram for serial shifting of 101 data in 3-bit shift register.
5. Define resolution, accuracy, settling time, monotonicity, and speed as related to DAC.
6. List the features of magnetic memories.
7. Explain the working principle of Dynamic RAM cell.
8. Compare PLA and PAL.
9. Describe briefly the operation of TTL NAND gate with circuit.
Part B
1. (a) Construct 4:1 multiplexer using 2:1 multiplexers.
(b)Illustrate use of multiplexer in implementation of simple Boolean functions with example.
2. a) Explain the role of BCD to 7–segment decoder in numbers display.
b) Discuss the role of control signals in demultiplexer circuit.
3. a) Explain the function of D flip-flop and also write truth-table.
b) Calculate the frequency at Q of JK flip-flop if it is triggered by 1 KHz clock signal under toggle mode, and sketch the input and output signals.
4. Show how to configure 555 timer as monostable multivibrator and astable multivibrator.
5. Construct a mod-7 counter and explain its functioning with the help of truth table and timing waveforms.
6. Show how to configure 7490 IC as decade counter and write its truth table.

7. Explain a binary ladder network of DAC with expression output. List its advantages.
8. (a) Calculate the resolution of a 4-bit DAC in terms of percentage of full-scale voltage
(b) For a 5-bit resistive divider, determine the following i) the weight assigned to the LSB.
ii) The change in the output voltage due to a change in the LSB. iii) The output voltage for  a digital input of 10110. Assume 0= 0 V and 1= + 10 V.
9. a) Calculate the number of address lines required to access 512 Kilo bytes of memory and calculate how many bytes of memory can be accessed with 15 address lines assuming byte addressable memory.
b) Identify the functional pins required for a typical RAM IC.
10. a) Explain the functioning of CMOS inverter.
b) List the voltage levels of TTL family.

The following are suggested institutional activities, to be carried out at least one during the semester. The course teacher/coordinator is expected to maintain the relevant record (Containing, Activity name, Resource persons and their details, duration, venue, student feedback, etc) pertaining to Institutional activities.

 Sl. No. Activity 1 Organize   Seminar,   workshop    or    Lecture   from   experts    on    the   modern trends/developments in digital electronics. 2 Organize hands-on practice on design and simulation of digital circuits. 3 Motivate students to take case study on different digital electronics-based mini projects to inculcate self and continuous learning.

Model Question Bank
Note: The questions in the question bank are indicative but not exhaustive. Sub-questions on different CLs may be combined to frame 10-marks questions or 10-marks questions given here can be splitted into 5-marks questions if necessary keeping weightage of CLs approximately intact and adhering to SEE end-exam pattern.

Unit-1: Combinational logic circuits Five-mark Questions
REMEMBER
1. Define combinational and sequential digital circuits with examples.
2. List any five combinational circuits and state their functions.
3. List any five sequential circuits and state their functions.
4. Define i) encoder, ii) decoder, iii) multiplexer, iv) demultiplexer, and v) priority encoder
5. Describe the demultiplexing function with the help of any demux circuit/IC
6. Describe the working of 4:1 multiplexer with the help of suitable diagram

7. Describe the multiplexing process with suitable digital multiplexer circuit.
8. Describe the working of simple priority encoder
9. Name the pin functions in any typical demultiplexer IC
10. List the truth-table entries of BCD to 7-sgement decoder
11. List the similarities and dissimilarities between encoders and multiplexers
12. Name the applications of multiplexer, demultiplexer, encoder, decoder and priority encoder
UNDERSTAND
1. Explain the working of any decoder with logic circuit
2. Explain the working of encoder with logic circuit
3. Explain how to implement the Boolean function y=AB¯+A̅B using a multiplexer IC
4. Compare encoder and decoder
5. Differentiate between multiplexer and demultiplexer
6. Demonstrate how BCD are displayed using combinational circuit
7. Differentiate between encoder and priority encoder
APPLICATION
1. Show how a 4-to-1 multiplexer can be realized using 2-to-1 multiplexers.
2. Show how to implement NAND function using a multiplexer IC
3. Construct 1:2 demultiplexer using gates and demonstrate its function
4. Write the truth table of 3 bit priority encoder
5. Calculate the control lines needed for 4:1 mux and 1:8 demux sketch the their logic diagrams

Ten-mark Questions

UNDERSTAND
1. Classify the combinational circuits and state the function and application of each category.
2. (a) Explain the role of BCD to 7 –segment decoder in numbers display
(b) Compare combinational and sequential digital circuits with examples
3. (a) Convert multiplexer to logic gate
(b) Discuss the role of control signals in demultiplexer circuit.

APPLICATION
1. (a) Construct 4:1 multiplexer using 2:1 multiplexers.
(b) Illustrate use of multiplexer in implementation of simple Boolean functions
2. (a) Demonstrate the use of BCD to 7-segment decoder in numbers display
(b) Write simple encoder circuit and its truth-table
3. (a) List any five applications of combinational circuits
(b) List any five pin functions of multiplexer IC
4. (a) Write simple decoder circuit and its truth table
(b) List the similarities between demultiplexer and demultiplexer

REMEMBER

Unit-2: Flip-flops and related circuits Five-mark Questions

1. Define flip-flop and list its applications
2. Describe different types of triggering flip-flops
3. Describe the functioning of RS flip-flop with gate-level circuit and truth table
4. List various flip-flops with logic diagrams.

5. Name the pins and their functions in a typical JK flip-flop.
6. Describe the functioning of D flip-flop with truth table
7. Locate the toggle state in the truth table of JK flip-flop and state its meaning and relevance
8. Describe how flip-flop can be used as divide-by-two counter with relevant waveforms
9. List the pin functions of 555 timer and name any two applications
UNDERSTAND
1. Differentiate between combinational and sequential circuits.
2. Explain the truth table of a D flip-flop and sketch the timing waveforms.
3. Distinguish between Preset and Clear inputs and briefly explain their significance
4. Illustrate race-around problem and discuss how it can be eliminated in JK flip-flops
5. Explain different types of triggering of sequential circuits
6. Modify JK flip-flop into D flip-flop
7. Convert JK into T flip-flop
8. List the ICs of RS, JK, JK-MS, D flip-flops and timer
APPLICATION
1. Calculate the frequency at Q of JK flip-flop if it is triggered by 1KHz clock signal under toggle mode, and sketch the input and output signals.
2. Show how 555 timer can be configured to generate 1KHz clock signal
3. Calculate the pulse width of unstable sate of 555-monostable multivibrator for a 4.7KΩ resistor and a 1.5 μF capacitor.
4. Show how to configure JK flip-flop as D flip-flop with truth table
5. Demonstrate how flip-flop can be used as memory cell

Ten-mark Questions
UNDERSTAND
1. (a) Explain the working of D-flip-flop with relevant diagram and waveform
(b) Demonstrate conversion of JK flip-flop into T flip-flop
2. (a) Compare sequential circuits with combinational circuits
(b) Compare T flip-flop with D flip-flop
3. (a) Explain the concept of racing condition and suggest methods to overcome this.
(b) Show how two JK flip-flops can be cascaded to act as divided-by-4 counter.
4. Explain the working of clocked RS flip-flop with the help of gate-level diagram, truth-table and timing and output wave forms.
5. (a) Compare 555 timer as astable multivibrator and monostable multivibrator
6. (b) Demonstrate how flip-flop can be used as single-bit memory cell.
7. Explain the internal diagram of IC555 timer and name its applications

APPLICATION
1. (a) Illustrate how JK flip-flop can be used as 1-bit memory element.
(b) Write gate-level circuit of clocked RS flip-flop and its truth table
2. (a) Calculate the frequency of the output at Q of a JK flip-flop when it is triggered by 100Hz signal under toggle state and justify your answer
(b) List the features of 555 timer IC
3. Show how to configure 555 timer as monostable multivibrator and astable multivibrator

REMEMBER

Unit 3: Registers and counters Five-mark Questions

1. Describe construction and working of 3-bit shift register
2. Define shift register and list different types of data movements in it
3. Describe the concept of universal shift register and list its applications
4. Define counter, modulus, register, up counting and down counting
5. List the pin functions of a typical IC counter
6. Name the applications of sequential circuits
7. Describe the functioning of mod -8 asynchronous counter with diagram
UNDERSTAND
1. Show how shift register can be realized using flip-flops
2. Explain shifting data bit-by-bit in a 3-bit shift register with relevant diagram
3. Sketch the timing diagram for serial shifting of 101 data in 3-bit shift register
4. Explain the working of 3-bit ring counter with truth-table and logic circuit
5. Compare Ring counter with Johnson counter
6. Differentiate between counter and shift register
7. Identify the applications of shift registers and counters
8. Relate number of flip-flops and modulus of a counter

APPLICATION
1. Write the truth table of 3-bit counter
2. Illustrate 3 bits can be stored in a 3-bit shift register
3. Construct 3-bit shift register to that can allow parallel movement of data
4. List pin functions of a typical shift register IC
5. Sketch the timing diagram/waveforms of a mod-6 counter
6. Sketch the timing diagram/waveforms of 3-bit ring counter
7. Compute the overall modulus of cascaded counter containing mod 2, mod5 and mod3, and justify your answer.

Ten-mark Questions

UNDERSTAND
1. (a) Compare Johnson counter and ring counter.
(b) Distinguish between synchronous counter and asynchronous counters.
2. (a) Compare SISO and PIPO operation of shift register with examples
(b) Distinguish between SIPO and PISO operation with examples.
3. Explain the functioning of a 3-bit shift register under SIPO and SISO modes.
4. Describe the operation of mod 8 counter with the help of circuit and truth table

APPLICATION
1. Construct a mod-7 counter and explain its functioning with the help of truth table and timing waveforms
2. (a) Show how flip-flops can be used to realise counter
(b) List different ways of data movement in shift registers
3. Show how to configure 7490 IC as decade counter and write its truth table
4. (a) Writ the truth table and circuit of mod 5 counter
(b)  Sketch the timing waveforms of a mod 5 counter
5. a) List the applications of counters and shift registers
(b) Construct a 3-bit counter that circulates the data.

Unit-4: Digital to Analog and Analog to Digital converters Five-mark Questions

REMEMBER
1. Define resolution, accuracy, settling time, monotonicity, and speed as related to DAC
2. Describe the functioning of a 4 bit ladder-type DAC
3. List the pin functions of a typical DAC IC
4. Describe briefly the operation of a 4-bit SAR DAC
5. List the specifications of ADC and define them
6. List the features of flash-type ADC

UNDERSTAND
1. Distinguish between DAC and ADC
2. Explain the need for ADC and DACs in computing
3. Identify the pins of a typical ADC IC and state their functions
4. Identify the different parts of SAR ADC and state their functions
5. Classify DAC circuits and compare them

APPLICATION
1. An 8-bit DAC produces an analog output of 12.5 mV for a digital input 00000010. Determine the analog output for a digital input of 00001011
2. Determine the resolution of a 12-bit A/D convertor having a full-scale analog input voltage of 5V.
3. An 8-bit D/A convertor has a step size of 20mv.Determine the full-scale output and percentage resolution

Ten-mark Questions

UNDERSTAND
1. Explain a binary ladder network of DAC with suitable diagram and expressions. List its advantages.
2. Explain the working of a 3-bit flash type ADC. List its advantages.
3. Explain the working of a successive approximation type ADC and compare its features with flash type ADC.
4. Explain the working of a dual-slope type ADC and summarize its advantages.

APPLICATION
1. Show how dual-slope ADC can be used to convert analog signal into digital form with circuit and relevant waveforms.
2. (a) Calculate the resolution of a 4 bit DAC in terms of percentage of full-scale voltage
(b) For a 5-bit resistive divider, determine the following i) The weight assigned to the LSB.
ii) The change in the output voltage due to a change in the LSB. iii) The output voltage for a digital input of 10110. Assume logical 0= 0 V and 1= + 10 V.

REMEMBER

Unit 5: Memories and programmable devices Five-mark Questions

1. Describe the role of memories in computers
2. List the memory types based on fabrication material and data retention
3. List the features of DDR memory
4. List the features of flash memory
5. List the features of magnetic memories
6. List he features of PLA
UNDERSTAND
1. Classify the memories based on speed and fabrication material
2. Distinguish between (i) ROM and RAM memories and (ii) Flash and Magnetic memories
3. Compare the features of static and dynamic RAM
4. Explain the working principle of Dynamic RAM cell
5. Relate the memory capacity and address range with examples
6. Compare PLA and PAL

APPLICATION
1. Calculate the address lines required to access 512 Kilo bytes of memory and calculate how many bytes of memory can be accessed with 15 address lines assuming byte addressable memory
2. Identify the functional pins required for RAM IC
3. Show how PAL can be used to implement simple Boolean expressions

Ten-mark Questions

UNDERSTAND
1. (a) Compare volatile and non-volatile memories
(b) Compare PLA and PAL
2. (a) Explain the working principle of static RAM cell
(b) Compare the features of DDR1 and DDR2 memories

APPLICATION
1. Show how the PAL–type array should be programmed in order to implement each of the following SOP expressions. Use a mark X to indicate an intact fuse. Simplify the expressions, if necessary.   a )  Y= AB¯ C + A̅BC̅ + ABC b)  Y = AB¯ C + A̅B¯ C + AB¯ C̅ + A̅BC
2. A certain memory is specified as 32k x8.Determine a) the number of bits in each word b) the number of words being stored c) the number of memory cells d) the number of address input lines, e) the number of data input lines and f) the number of data output lines.
3. The 2125A is a static RAM IC that has a capacity of 1Kx1, one active-LOW chip select input, and separate data input and output. Show how to combine several 2125A ICs to form a 1Kx8 module.
4. Two 16 MB RAMS are used to build a RAM capacity of 32 MB. Show the configuration and also state the address inputs for which the two RAMs will be active. The two RAMs have common I/O pins, a write enable input that is active-LOW, and a chip select input that is active –HIGH.
5. (a) List the features and applications of E2PROM.
(b) List types and features of disk memories.
6. (a) Explain accessing process in (i) Magnetic memories and (ii) RAM

(b) List the features of DDR memory

REMEMBER

Unit 6: Digital integrated circuits Five-mark Questions

1. Define fan-in, fan-out, propagation delay, power dissipation and noise margin as applicable to logic families
2. Describe briefly the operation of TTL NAND gate with circuit
3. List the features of ECL family
4. List the features of CMOS family
UNDERSTAND
1. Compare CMOS family with TTL family
2. Distinguish between HMOS and CHMOS
3. Explain the functioning of CMOS inverter
4. Classify the Integrated circuits based on the scale of integration.

APPLICATION