Second Semester_Digital Logic_Simplification of Boolean Functions
3.1 Simplification of Boolean Algebra using Boolean Rules
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Boolean Algebra: Mathematical framework for analyzing logic circuits.
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Basic Rules / Laws:
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Identity Law: A + 0 = A, A·1 = A
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Null Law: A + 1 = 1, A·0 = 0
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Idempotent Law: A + A = A, A·A = A
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Complement Law: A + A' = 1, A·A' = 0
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Distributive Law: A·(B + C) = A·B + A·C
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De Morgan’s Theorems:
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(A·B)' = A' + B'
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(A + B)' = A'·B'
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Purpose: Reduce complexity of logic circuits and minimize number of gates.
3.2 Karnaugh Map (K-Map) Method
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K-map: Graphical method to simplify Boolean expressions.
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Maps: 2, 3, or 4 variables (can extend to 5-6, but rare in exams).
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Steps:
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Fill K-map using truth table.
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Group 1’s in powers of 2 (1, 2, 4, 8…).
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Derive simplified expression for Sum of Products (SOP).
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Don’t Care Conditions (X): Inputs that won’t occur, can be used to simplify further.
3.3 Canonical and Standard Forms
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Canonical Forms:
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Sum of Minterms (SOP): Expression written as sum of AND terms representing 1s in the truth table.
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Product of Maxterms (POS): Expression written as product of OR terms representing 0s in the truth table.
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Standard Forms: Simplified version of canonical forms for implementation.
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Purpose: Provides systematic method for logic design and circuit realization.
3.4 NAND and NOR Implementation
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Universal Gates: Can implement any Boolean function using only NAND or NOR gates.
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NAND Implementation: Convert all AND, OR, NOT using NAND gates.
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NOR Implementation: Convert all AND, OR, NOT using NOR gates.
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Advantage: Cost-effective in digital IC design.
3.5 Quine-McCluskey Method
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Tabular Method: Systematic algorithm for minimizing Boolean functions, especially for more than 4 variables.
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Steps:
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List all minterms.
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Group minterms by number of 1s.
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Compare minterms to find prime implicants.
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Use prime implicant chart to find essential prime implicants.
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Useful for computer-aided design (CAD) of logic circuits.
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