Mastering the Sum of Product and Product of Sum: A Comprehensive Guide

Mar 16, 20243 min read

In Boolean algebra, representing functions with different forms helps understand, optimize, and implement them :

Sum of Products (SOP):  A function expressed as a sum of product terms (minterms). Each term represents a combination of variables where the output is True. It considers all possible minterms and includes only those relevant to the function.
Product of Sums (POS):  A function expressed as a product of sum terms (max terms). Each term represents a combination of variables where the output is False. It considers all possible maxterms and excludes those relevant to the function.

Standard Forms:

Standard SOP/POS:  A version of SOP/POS where each variable appears in every term either uncomplemented (True) or complemented (False). This ensures a consistent and simpler representation.

Minterms and Maxterms:

Minterm:  A product term representing a single combination of variables where the function is True. Example: For three variables A, B, C, the minterm ABC represents the combination where all three variables are True.
Maxterm:  A sum term representing a single combination of variables where the function is False. Example: For A, B, C, the maxterm (A + B' + C') represents the combination where either A is False or B is True or C is True (or any combination where not all variables are True).

Example:

Consider a function F(A, B, C) that outputs True when either A and B are True or B and C are True, but not both.

Canonical SOP: F = AB + BC (Only the two relevant minterms are included)
Canonical POS: F = (A + C')(B + C') (Excludes the maxterms where AB and BC are both True)
Standard SOP: F = AB + A'BC (Each variable appears in both forms)
Standard POS: F = (A + C')(B + C')(A' + B + C) (Each variable appears in both forms)

Que. Convert the following Boolean expression to standard SOP form:

F(A, B, C) = (A' + B)C' + B'.

Soln -   F = (A'C' + BC') + B'

F = A'C' + BC' + A'B' + B'B'

F = A'C' + BC' + A'B'

Que. Express the following Boolean function with a maxterm product:

F(A, B, C) = AB + A'C'.

Soln - m5 (101), m7 (111).

M5' = (A' + B' + C), M7' = (A + B + C').

F = M5' M7' = (A' + B' + C) (A + B + C')

Advantages of  Canonical Form:

Uniqueness: A Boolean function's canonical form is unique, meaning that a given function can only have one conceivable canonical form.
Clarity: A Boolean function's canonical form offers a straightforward and unambiguous description of the function.
Completion: Regardless of its complexity, any Boolean function that exists can be represented by its canonical form.

Disadvantages of Canonical Form:

Complexity: The canonical form of a boolean function can be complex, especially for functions with many variables.
Computation: Computing the canonical form of a boolean function can be computationally expensive, especially for large functions.
Redundancy: The canonical form of a boolean function can be redundant, which means that it can contain unnecessary terms or variables that do not affect the function.

Advantages of Standard Form:

Simplicity: The standard form of a boolean function is simpler than the canonical form, making it easier to understand and work with.
Efficiency: The standard form of a boolean function can be implemented using fewer logic gates than the canonical form, making it more efficient in hardware and computation.
Flexibility: The standard form of a boolean function can be easily modified and combined with other functions to create new functions that meet specific design requirements.

Disadvantages of Standard Form:

Non-uniqueness: The standard form of a boolean function is not unique, which means that there can be multiple possible standard forms for a given function.
Incompleteness: The standard form of a boolean function may not be able to represent some complex boolean functions. Ambiguity: The standard form of a boolean function can be ambiguous, especially if it contains multiple equivalent expressions.