Page 94 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Unit 5: Combinational Circuits

Binary encoder: It encodes information from 2n inputs into an n-bit code. Exactly one of the input Notes
signals should have a value of 1, and the outputs present the binary number that identifies which
input is equal to 1.
Decoder: This circuit is used to decode encoded information. A binary decoder is a logic circuit
with n inputs and 2n outputs.
Priority encoder: Here each input has a priority level associated with it the encoder outputs
indicate the active input that has the highest priority.
Segment decoder: It converts one binary-coded decimal (BCD) digit into information suitable for
driving a digit-oriented display.
Subtractor: This circuit takes two binary numbers as input and subtracts one binary number input
from the other binary number input. Similar to adders, it gives out two outputs, difference and
borrows (carry–in the case of Adders).

1. Write logic equations of half adder and draw circuit diagram.
2. Draw a circuit diagram for 3-to-8 decoder using two 2-to-4 decoders.

5.7 Review Questions

1. Describe the adder in brief. And draw the circuit diagram.
2. What do you understand by comparators?
3. Define the BCD-to-7-segment decoder.
4. What is subtractor? Define the types of subtractor.
5. What do you understand by encoder? Draw the circuit diagram.

6. What do you understand by decoder? Write the truth table.
7. Differentiate between half adder and full adder.
8. Write the truth table of full adder.
9. Differentiate between half subtractor and full subtractor.
10. Explain the Priority Encoders.
Answers to Self Assessment

1. (c) 2. (b) 3. (a) 4. (b) 5. (d)
6. (a) 7. (b) 8. (d) 9. (a)

5.8 Further Reading

Digital Fundamentals: Ninth Edition, by Floyd Thomas L.

http://www.ariese.articlealley.com/combinational-circuit-design-165328.
html

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