Digital Circuit Systems

Digital Electronics Viva Question (Part-2)

Digital Electronics Viva Question

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Digital Electronics Viva Questions (Part-1)

Short Questions and Answers

Q.1. What are logic levels?

Ans. In a positive logic system, the logic levels are usually +5 V for logic 1 and 0 V for logic 0 and in a negative logic system, they are +5 V for logic 0 and 0 V for logic 1. In practice, 0 V to 0.8 V is treated as logic 0 and 2 V to 5 V is treated as logic 1. The 2 V to 5 V range is invalid and the response is unpredictable.

Q.2. What is the difference between periodic and non-periodic pulse waveforms?

Ans. A periodic pulse waveform is one that repeats itself at regular intervals of time called the period (T). It has the same pulse width throughout. A non-periodic pulse waveform is one that does not repeat itself at regular intervals of time and may be composed of pulses of different pulse widths and/or different time intervals between the pulses.

Q.3. What is the duty cycle?

Ans. The duty cycle of a periodic pulse waveform is the ratio of the ON time to the period of the waveform.

Q.4. What is the frequency?

Ans. The reciprocal of the time period of a waveform is called frequency.

Q.5. What is encoding? What is an encoder?

Ans. Encoding b the process of convening a familiar number or symbol to some coded form. An encoder is a digital device that performs the operation of encoding, i.e. an encoder is a digital device that receives digits or alphabets, or special symbols and converts them into their respective binary codes.

Q.6. What is decoding? What is a decoder?

Ans. Decoding is the inverse operation of encoding, i.e. it is the process of convening the binary coded information to unique outputs. A decoder is a digital device that performs the operation of decoding, i.e., a decoder converts binary coded information to unique output such as digits, symbols, alphabetic characters, etc.

Q.7. What is multiplexing? What is a multiplexer?

Ans. Multiplexing means sharing. It is the process of switching information from several lines onto a single line in a specified sequence. A multiplexer or data selector is a logic circuit that accepts several data – inputs and allows only one of them to get through to the output.

Q.8. What is demultiplexing? What is a demultiplexer?

Ans. Demultiplexing is the inverse operation of multiplexing, i.e. demultiplexing is the process of switching information from one input line onto several output lines. A demultiplexer is a digital device that performs the operation of demultiplexing, i.e. a demultiplexer is a digital circuit that takes a single input and distributes it over several outputs. It is a 1-to-N device.

Q.9. What is a comparator?

Ans. A comparator is a logic circuit used to compare two quantities and give an output signal indicating whether the two input quantities are equal or not, and if not, which of them is greater.

Q.10. What is a code convener?

Ans. A code converter is a logic circuit used to convert information coded in one form to another form.

Q.11. What are registers?

Ans. Digital circuits used for temporary storage and shifting of information (data) are called registers.

Q.12. What are the basic methods for the transmission of digital information?

Ans. The two basic methods for the transmission of digital information are (a) serial data transmission and (b) parallel data transmission.

Q.13. Compare serial and parallel data transmission?

Ans. In parallel data transmission, all the bits are transmitted simultaneously. So one connecting line is required for each bit. Though data transmission is faster, the number of lines used between the transmitter and the receiver is more. This system is therefore complex and costly. On the other hand, in serial transmission, the information is transmitted bit-by-bit. So only one connecting line is sufficient between the transmitter and the receiver. Hence, serial transmission is simpler and cheaper but slower.

Q.14. What is a monolithic IC?

Ans. A monolithic IC is an electronic circuit that is constructed entirely on a single piece of semiconductor material (usually silicon) called substrate, which is commonly referred to as a chip.

Q.15. What are the advantages and drawbacks of ICs? Why cannot ICs handle large voltages and currents?

Ans. ICs have the advantages of low cost, low power, smaller size, and high reliability over discrete circuits. The disadvantages of ICs are: ICs cannot handle very large voltages or currents, and ICs cannot easily implement certain electrical devices such as precision resistors, inductors, transformers and large capacitors.

Q.16. Why ICs cannot handle large voltages and currents?

Ans. ICs cannot handle very large voltages or currents as the heat generated in such devices would cause the temperature to rise beyond acceptable limits resulting in the burning out of ICs.

Q.17. How are ICs classified?

Ans. ICs may be classified as analog (linear) ICs and digital ICs.

Q.18. Distinguish between digital and analog ICs.

Ans. Digital ICs are complete functioning blocks. No additional components are required for their operation. The output may be obtained by applying the input. Analog ICs are not complete functioning blocks. External components are required for their operation.

Q.19. What are the two main types of IC packages?

Ans. The two main types of IC packages arc: dual-in-line package and flat-package.

Q.20. How are digital ICs classified?

Ans. Depending on the principal components used digital ICs may be classified as unipolar ICs and bipolar ICs. In terms of the gate circuits per chip, digital ICs may be classified as SSI, MSI. LSI, VLSI, and ULSI.

Q.21. What are the different levels of integration? Give examples?

Ans. The different levels of integration based on the number of gate circuits per chip are as follows

  • Small scale integration SSI (less than 12 gate circuits per chip). Logic gates and flip.fk„ belong to this category.
  • Medium scale integration MSI (12 to 99 gate circuits per chip). Encoders, decoders, multiplexers, demultiplexers, counters, registers, and arithmetic circuits fall in this category.
  • Large scale integration LSI (100 to 9999 gate circuits per chip). Small memories and small microprocessors fall into this category.
  • Very large scale integration VLSI (10,000 to 99.999 gate circuits per chip). Large memories and large microprocessor systems belong to this category.
  • Ultra large scale integration ULSI (more than 1,00,000 gate circuits per chip). Very large memories and large microprocessor systems and single chip computers fall into this category.

Q.22. What is a microprocessor?

Ans. A microprocessor is an LSI/VLSI device that can be programmed to perform arithmetic and logic operations and other functions in a prescribed sequence for the movement and processing of data.

Q.23. What is a digital computer?

Ans. A digital computer is a system of hardware that performs arithmetic operations, manipulates data, and makes decisions.

Q.24. What are the major parts of a digital computer?

Ans. The five major functional units of a digital computer are (1) input unit, (2) memory unit. (3) control unit, (4) arithmetic logic unit, and (5) output unit.

Q.25. What are the basic classifications of computers?

Ans. The three basic classifications of computers are microcomputer, minicomputer, and mainframe. This classification is based on their physical size.

Q.26. What is a program?

Ans. The set of instructions that tells a computer what to do is called a program.

Q.27. Name the IC fabrication technologies currently in use?

Ans. The integrated circuit fabrication technologies currently in use are TTL. ECL, IIL, MOS, and CMOS technologies.

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