Digital Logic · Unit 4
Combinational Logic Circuits
Exam-focused notes for Combinational Logic Circuits (Digital Logic, BIT103): what the TU syllabus asks and how it has actually been tested, with 10 solved past questions from this unit.
What this unit covers
- Half adder and full adder design
- Half subtractor and full subtractor design
- Binary parallel adder
- Magnitude comparator circuits
- Combinational circuit design methodology
Combinational circuit design methodology
Design a combinational circuit with three inputs. The output is 1 when the binary value of the input is odd.[10]
Design a combinational circuit with three inputs (A, B, C) where the output F = 1 when the binary value of the inputs is odd. --- Signal Description --------------------- A Most Significant Bit (MSB) B Middle Bit C Least Significant Bit (LSB) F Output (1 if...
Full solved answer →Define combinational logic circuit. Design a combinational circuit whose input is a four-bit number and output is the 1's complement of the input number.[10]
A combinational logic circuit is a digital circuit in which the output at any instant of time depends only on the present input values and not on any previous inputs or outputs. There is no memory element involved; the circuit has no feedback path. Key char...
Full solved answer →Design a combinational circuit with four inputs and one output. The output is equal to 1 when (i) all the inputs are equal to 1 or (ii) none of the inputs are equal to 1 or (iii) an odd number of inputs are equal to 1.[10]
Let the four inputs be A, B, C, D and output be F. Output F = 1 when: 1. All inputs are 1 (i.e., ABCD = 1111) 2. None of the inputs are 1 (i.e., ABCD = 0000) 3. An odd number of inputs are 1 (i.e., exactly 1 or exactly 3 inputs are 1) --- List all 16 minter...
Full solved answer →Design a combinational circuit whose input is a four-bit number and output is 2's complement of the input number.[10]
The 2's complement of a binary number is obtained by: 1. Taking the 1's complement (inverting all bits), then 2. Adding 1 to the result For a 4-bit input A = A₃A₂A₁A₀, the output is S = S₃S₂S₁S₀ --- The 2's complement of N is: S = 2⁴ - N = 16 - N A₃ A₂ A₁ A...
Full solved answer →Magnitude comparator circuits
Define magnitude comparator?Design a 4-bit magnitude comparator circuit.[2+8]
A magnitude comparator is a combinational logic circuit that compares two binary numbers and determines their relative magnitudes. Given two n-bit numbers A and B, the comparator produces three output signals: - A B (output is HIGH when A is greater than B)...
Full solved answer →What is magnitude comparator? Design 2-bit magnitude comparator. [5]
A magnitude comparator is a combinational circuit that compares two binary numbers and determines their relative magnitudes. It produces three outputs indicating whether: - A B - A = B - A < B --- Let the two 2-bit numbers be: - A = A₁A₀ - B = B₁B₀ A₁ A₀ B₁...
Full solved answer →Half subtractor and full subtractor design
Define Half-subtractor with truth table and logic diagram. [5]
A half-subtractor is a combinational logic circuit that performs subtraction of two single-bit binary numbers. It produces two outputs: the Difference (D) and the Borrow (B). - It subtracts the subtrahend (B) from the minuend (A) - It does not account for a...
Full solved answer →Define Half-subtractor with truth table and logic diagram. [5]
A half-subtractor is a combinational logic circuit that performs subtraction of two single-bit binary numbers. It produces two outputs: the Difference (D) and the Borrow (B). - It subtracts the subtrahend (B) from the minuend (A) - It does not account for a...
Full solved answer →Implement a full subtractor with two half subtractors and one OR Gate. [5]
A Half Subtractor subtracts two single bits (A and B) and produces: - Difference: D = A ⊕ B - Borrow: Bout = A'B A B D Bout ---------------- 0 0 0 0 0 1 1 1 1 0 1 0 1 1 0 0 --- A Full Subtractor subtracts three bits: A (minuend), B (subtrahend), Bin (borrow...
Full solved answer →Binary parallel adder
Write short notes on Binary parallel adder Write short notes on Jonson counter. [2.5+2.5]
--- A binary parallel adder is a combinational circuit that adds two binary numbers simultaneously (in parallel) by connecting multiple Full Adders (FA) in cascade. - To add two n-bit binary numbers, n full adders are connected in series such that the carry...
Full solved answer →Make Unit 4 stick
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