Tag: sr flip flop vs jk flip flop

JK Flip Flops

What is JK Flip Flop?

 

JK flip flop is a refined and improved version of the SR flip flop that has been introduced for solving the problem of indeterminate state that occurs in SR flip flop when both the inputs are 1.

In JK flip flop,

  • Input J behaves like input S of SR flip flop which was meant to set the the flip flop.
  • Input K behaves like input R of SR flip flop which was meant to reset the the flip flop.

 

Difference between JK Flip Flop and SR Flip Flop-

 

Functionally, both JK flip flop and SR flip flop are same with only one difference.

The only difference between SR flip flop and JK flip flop is that in JK flip flop, indeterminate state does not occur.

Instead of indeterminate state, in JK flip flop, the present state toggles i.e. the present state gets inverted when both the inputs are 1.

 

Construction of JK Flip Flop-

 

JK flip flop can be constructed in two ways-

  1. By using SR flip flop constructed using NOR latch
  2. By using SR flip flop constructed using NAND latch

 

Remember

JK Flip Flop = SR Flip Flop + 2 other connections

 

Way-01: Construction of JK Flip Flop by using SR Flip Flop constructed using NOR latch-

 

Here, we use SR flip flop constructed using NOR latch and two other connections to construct the JK flip flop.

 

Logic Circuit-

 

 

Way-02: Construction of JK Flip Flop by using SR Flip Flop constructed using NAND latch-

 

Here, we use SR flip flop constructed using NAND latch and two other connections to construct the JK flip flop.

 

Logic Circuit-

 

 

Logic Symbol-

 

 

Truth Table-

 

INPUTSOUTPUTS
JKQn

(Present State)

Qn+1

(Next State)

0000
0011
0100
0110
1001
1011
1101
1110

 

The above table can be reduced as-

 

INPUTSOUTPUTSREMARKS
JKQn

(Present State)

Qn+1

(Next State)

States and Conditions
00XQnHold State condition J = K = 0
01X0Reset state condition J = 0 , K = 1
10X1Set state condition J = 1 , K = 0
11XQ’nToggle state condition J = K = 1

 

Characteristic Equation-

 

Draw a k map using above truth table-

 

 

Qn+1 = Q’n (JK + JK’) + Qn (J’K’ + JK’)

Qn+1 = Q’nJ + QnK’

 

Excitation Table-

 

We will draw excitation table of any flip flop using its truth table.

 

What is excitation table?

For a particular combination of present state Qn and next state Qn+1, excitation table tell the inputs required.

 

QnQn+1SR
000X
011X
10X1
11X0

 

 

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