Counters in Digital Logic

Types of Ring Counter

Straight Ring Counter

A straight Ring Counter is also known as One hot counter. The result of the previous flip-flop is used as an input to the first flip-flop. The ORI input is connected to the PR input of the first flip flop and the clear input of the other flip flops in the ring counter.

Twisted Ring Counter

It's also known as a Johnson counter, a switch-tail ring counter, or a walking ring counter. It circulates a stream of ones followed by zeros around the ring by connecting the complement of the output of the final shift register to the input of the first register.

Binary Counter

A binary counter connects several flip-flop circuits. The flip-flops change state with every clock pulse, producing a binary number for digital timers. Binary synchronous counters in digital logic eliminate the settling time issue of ripple counters. These counters use count pulses. This counter is sometimes known as a "ripple through" counter.

All flip-flops's control inputs Clk are connected directly. A 4-bit binary counter's state and block diagram are given below:

State Diagram

As demonstrated below, a 4-bit binary synchronous counter with count enable function may be implemented:

Block Diagram of a Binary Counter

Working

Each flip-flop's J and K inputs are set to 1 to create a toggle at each clock input cycle. A toggle is made in the second cell for every two toggles in the first cell and so on down to the fourth cell. This yields a binary number equal to the input clock signal's number of cycles.

Truth Table

Johnson Counter

The Ring counter and the Johnson counter are pretty similar. The main difference between the Johnson counters and the ring counters in digital logic is that the last flip flop's result is supplied as an input to the first flip flop. The inverted outcome Q' of the last flip flop, on the other hand, is provided as an input in the Johnson counter. The Johnson counter's remaining tasks are similar to a ring counter. The Creeping counter is another name for the Johnson counter.

In a Johnson Counter,

1. No. of states in Johnson counter = No. of flip-flops used  
2. Number of used states = 2n
3. Number of unused states = 2n - 2*n

State Diagram

Block Diagram of a Johnson Counter

The 4-bit Johnson counter uses four D flip flops, similar to the Ring counter, and the same clock pulse is applied to all of the flip flops' inputs.

Truth Table

Ripple Counter

A ripple counter is an asynchronous counter in which the clock pulse ripples through the circuit. The n-MOD ripple counter is created by mixing n flip-flops. The n-MOD ripple counter may count 2ⁿ states before resetting to its starting value.

State Diagram

Block Diagram of a Ripple Counter

What's Happening here

The circuit of a binary ripple counter is depicted in the diagram above. J0K0 and J1K1 are the two JK flip flops used here. Flip flops' JK inputs are provided with a high voltage signal that keeps them in state 1. The symbol representing the clock pulse shows a negative triggered clock pulse. The output Q0 of the first flip flop is applied as a clock pulse to the second flip flop, as shown in the diagram.

Truth Table

The fourth condition of the JK flip flop happens when high voltage is applied to the inputs of the flip flops. When we supply high voltage to the input, the flip-flops will be in state 1. As a result, at the negative going end of the clock pulse, the states of the flip flips passes are toggled. 

Here's the truth table of the J-K flip flop for relativity.

Working

When the negative clock edge passes through the flip flop, the state of the output Q0 changes. All of the flip-flops are initially set to 0. These flip-flops change states when the passed clock goes from 1 to 0. When the inputs of the flip flops are all one, the JK flip flop toggles, changing its state from 0 to 1. The procedure is the same for all clock pulses.

The clock pulse from the first flip flop is sent to the second. The state of the second flip flop is changed when the output Q0 transitions from 1 to 0. Q0 and Q1 are treated as LSB and MSB, respectively. The counter keeps track of the numbers 00, 01, 10, and 11. After counting these figures, the counter resets itself and begins counting anew from 00, 01, 10, and 1. Count values until clock pulses are sent to the J0K0 flip flop.

Must Read Shift Registers in Digital Electronics

Frequently Asked Questions

What is a counter in digital logic?

A counter is a device in digital logic that keeps track of (and occasionally shows) the number of times a specific event or process has occurred, usually connected to a clock signal. It helps maintain the process synchronisation.

What are ring counters and Johnson counters?

A ring counter is a specific Serial IN Serial OUT Shift register application. The Ring counter and the Johnson counter are pretty similar. The main difference between the Johnson and ring counters in digital logic is that the last flip-flop's result is supplied as input to the first flip-flop. 

Why JK flip flop is used in counters?

In digital logic designing, the JK flip-flops are used in counters. Using a JK flip-flop is important because, based on the clock pulse, it can change its state if both inputs are high.

Which IC is used in the ring counter?

The term "integrated circuit" (abbreviated as "IC") refers to any semiconductor-based chip that contains an integrated collection of digital circuitry. The IC components required for ring counters are IC 74164 and IC 7404.

Conclusion

In this article, we have extensively discussed four main counters in digital logic, with how they are built and work along with the truth table curated upon the input signal provided to the flip flops used in the counters in digital logic.

We hope that this blog has helped you enhance your knowledge regarding counters used in digital logic and if you would like to learn more, check out our articles on  Code Studio. Do upvote our blog to help other ninjas grow. Happy Coding!