Introduction of K-Map (Karnaugh Map)

In many digital circuits and practical problems, we need to find expressions with minimum variables. We can minimize Boolean expressions of 3, 4 variables very easily using K-map without using any Boolean algebra theorems. It is a tool which is used in digital logic to simplify boolean expression. It helps to simplify logic into simpler form by organizing grid from truth table values. This helps it to create a minimal Boolean expressions by identifying patterns.

K-map can take two forms:

1. Sum of product (SOP)
2. Product of Sum (POS)

According to the need of problem. K-map is a table-like representation, but it gives more information than the TABLE. We fill a grid of the K-map with 0’s and 1’s then solve it by making groups.

Steps to Solve Expression using K-map

1. Select the K-map according to the number of variables.
2. Identify minterms or maxterms as given in the problem.
3. For SOP put 1’s in blocks of K-map respective to the minterms (0’s elsewhere).
4. For POS put 0’s in blocks of K-map respective to the max terms (1’s elsewhere).
5. Make rectangular groups containing total terms in power of two like 2,4,8 ..(except 1) and try to cover as many elements as you can in one group.
6. From the groups made in step 5 find the product terms and sum them up for SOP form.

SOP FORM(Sum of Product Form)

SOP form is way to simplify and write Boolean expressions using AND to combine inputs and OP to combine the results.

1. K-map for 2 variables

In the 2 variable k-map, four squares are constructed. Each square contains one term of expression with two variables.

K-Map for 2 variables

2. K-map of 3 variables

K-map SOP form for 3 variables

Z= ΣA,B,C(1,3,6,7)  

From red group we get product term: 

A’C 

From green group we get product term: 

AB 

Summing these product terms  we get- Final expression (A’C+AB) 

3. K-map for 4 variables

K-map 4 variable SOP form

F(A,B,C,D)=Σ(0,2,5,7,8,10,13,15)  

k map 4 variables

From red group we get product term: 

AB

From green group we get product term: 

A'B'

Summing  these product terms  we get- Final expression (AB+A’B’).

POS FORM (Product of Sum Form)

POS form is a way to simplify and write Boolean expressions using OR to combine terms inside parentheses and then AND to combine those groups.

1.K-map of 2 variables

In the 2 variable k-map, four squares are constructed. Each square contains one term of expression with two variables.

K-map of 2 variables

2. K-map of 3 variables

K-map 3 variable POS form

F(A,B,C)=Σ(0,3,6,7)

 From red group we find terms 

A    B   

Taking complement of these two 

A'     B'    

Now sum up them 

(A' + B') 

From brown group we find terms 

B   C 

Taking complement of these two terms 

B’  C’ 

Now sum up them 

(B’+C’) 

From yellow group we find terms 

A' B' C’ 

Taking complement of these two 

A B C 

Now sum up them 

(A + B + C) 

We will take product of these three terms : Final expression –

(A' + B’) (B’ + C’) (A + B + C) 

3. K-map of  4 variables  

K-map 4 variable POS form

F(A,B,C,D)=Σ(3,5,7,8,10,11,12,13) 

From green group we find terms 

C’  D  B 

Taking their complement and summing them 

(C+D’+B’) 

From red group we find terms 

C  D  A’ 

Taking their complement and summing them 

(C’+D’+A) 

From blue  group we find terms

A  C’  D’ 

Taking their complement and summing them 

(A’+C+D) 

From brown  group we find terms

A  B’  C 

Taking their complement and summing them 

(A’+B+C’) 

Finally we express these as product –

(C+D’+B’).(C’+D’+A).(A’+C+D).(A’+B+C’) 

Advantages of K-MAP

• Makes Logic Simpler: It makes complicated Boolean expressions simpler.
• Minimizes Logic Gates: Simplifying the logic helps us to use fewer logic gates, making circuits more efficient.
• Reduce Errors: The visual representation of k-map helps to avoid errors while simplifying.
• Time-Saving: It’s quicker than traditional methods for simplifying logic.
• No need for Boolean Laws: K-map doesn’t require deep knowledge of Boolean laws, making it easy for beginners.

Disadvantages of K-MAP

• Limited to Fewer Variables: K-maps are best suited for 2 to 4 variables and above it, process becomes hard and complicated to manage.
• Not suitable for all functions: In some cases, its hard to group terms correctly, leading to errors and making simplification difficult.
• Space Limitations: As the number of variables increases, the K-map grid becomes too large to handle easily.
• Requires Careful Grouping: Sometimes incorrect grouping of terms can cause mistakes in logic simplification.

Also attempt Quiz on K-MAP .

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Article Tags :

• Digital Logic