# 7 Difference Between Ring Counter And Johnson Counter

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## What Is A Ring Counter?

A ring counter is a type of counter composed of flip-flops connected into a shift register, with the output of the last flip-flop fed to the input of the first, making a ‘’circular’’ or ‘’ring’’ structure.

There are two types of ring counters:

• Straight ring counter-connects the output of the last shift register to the first shift register input and circulates a single one (or zero) bit around the ring.
• Twisted ring counter-connects the complement of output of the last shift register to the input of the first register and circulates a stream of ones followed by zeros around the ring.

### What You Need To Know About Ring Counter

• Ring counter is mostly used in successive approximation type ADC and stepper motor control.
• In ring counter, the output of the last flip flop is connected to the input of the first flip flop.
• Decoding is easy in ring counter as the number of states is equal to the number of flip flops.
• If ‘n’ is the number of flip flops that is used in ring counter, the number of possible states is ‘n’. That means the number of states is equal to the number of flip flops used.
• In ring counter, if input frequency is f in ring counter then the output is f/n.
• The total number of unused states in the ring counter is (2^n-n).

## Jonson Counter

A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first. It is referred to as Inverse Feedback Counter. The register cycles through a sequence of bit-patterns. The MOD of the Johnson counter is 2n if n flip-flops are used. The main advantage of the Johnson counter is that it only needs half the number of flip-flops compared to the standard ring counter for the same MOD.

### What You Need To Know About Johnson Counter

• Johnson counter is also referred to as walking counter or  switching tail counter and is mostly used in phase shift or function generator.
• In Johnson counter, the output bar or Q-bar of the last flip flop is connected to the input of the first flip flop.
• Decoding Johnson counter is complex as compared to ring to counter.
• If ‘n’ is the number of flip flop used in Johnson counter, then the total number of states used is ‘2n’.
• In Johnson counter, if input frequency is ‘f’ then the output is ‘f/2n’.
• The total number of unused states in Johnson counter is (2^n-2n).

## Difference Between Ring Counter And Johnson Counter In Tabular Form

 BASIS OF COMPARISON RING COUNTER JOHNSON COUNTER Application Ring counter is mostly used in successive approximation type ADC and stepper motor control. Johnson counter is also referred to as walking counter or  switching tail counter and is mostly used in phase shift or function generator. Output In ring counter, the output of the last flip flop is connected to the input of the first flip flop. In Johnson counter, the output bar or Q-bar of the last flip flop is connected to the input of the first flip flop. Decoding Decoding is easy in ring counter as the number of states is equal to the number of flip flops. Decoding Johnson counter is complex as compared to ring to counter. Number Of Flip-Flops Vs Number Of Possible States Used If ‘n’ is the number of flip flops that is used in ring counter, the number of possible states is ‘n’. That means the number of states is equal to the number of flip flops used. If ‘n’ is the number of flip flop used in Johnson counter, then the total number of states used is ‘2n’. Input Frequency In Johnson counter, if input frequency is ‘f’ then the output is ‘f/2n’. In Johnson counter, if input frequency is ‘f’ then the output is ‘f/2n’. Unused States The total number of unused states in Johnson counter is (2^n-2n). The total number of unused states in Johnson counter is (2^n-2n).
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