4-bit Johnson Counter Simulator

This simulator demonstrates the operation of a 4-bit Johnson counter (also known as a twisted-tail ring counter). The Johnson counter is a shift register where the inverted output of the last flip-flop is fed back to the input of the first flip-flop.

Counter Controls

Speed:
Current State:
0
0
0
0
Step Count: 0 / 8

Johnson Sequence

A 4-bit Johnson counter cycles through 8 distinct states:

0:
0
0
0
0
1:
1
0
0
0
2:
1
1
0
0
3:
1
1
1
0
4:
1
1
1
1
5:
0
1
1
1
6:
0
0
1
1
7:
0
0
0
1

Circuit Diagram

The circuit diagram below shows how a 4-bit Johnson counter is implemented using D flip-flops. Notice how the inverted output Q' of the last flip-flop is connected to the input D of the first flip-flop.

D Flip-Flop 3
0
Q
0
Q'
1
D Flip-Flop 2
0
Q
0
Q'
1
D Flip-Flop 1
0
Q
0
Q'
1
D Flip-Flop 0
0
Q
0
Q'
1

About Johnson Counters

The Johnson counter (also known as a twisted ring counter) is a modified shift register where the inverted output of the last flip-flop is fed back to the input of the first flip-flop. This creates a sequence that cycles through 2n states for n flip-flops, making it twice as efficient as a standard ring counter.

Key characteristics of a Johnson counter: