Asynchronous Counter

By Priyanshu Vaish|Updated : August 26th, 2022

The Asynchronous Counter is made of two words asynchronous and counter. The word Asynchronous refers to managing the operation timing in a computer or communications stream by delivering a pulse only when the preceding operation is done rather than sending it at regular intervals.

A counter is a device that can count any specific event based on how many times that event(s) occurs. Therefore, An Asynchronous counter can count using Asynchronous clock input. An Asynchronous counter can count 2n- 1 possible counting states. Here, we will see the Asynchronous Counter in detail along with its applications, advantages, and disadvantages, along with knowing what "Asynchronous Counter is also known as".

What is an Asynchronous Counter?

Asynchronous counters have an output that is independent of the clock signal. Because the flip flops in asynchronous counters are provided with distinct clock signals, the output may be delayed. The number of logic gates required to build asynchronous counters is quite small. As a result, their design is straightforward. The asynchronous counter is also known as "Ripple counters".

The number of flip-flops needed in a ripple counter is determined by the number of counter states (ex: Mod 4, Mod 2, etc.). The number of output states of a counter is referred to as its "Modulus" or "MOD." A counter can have a maximum of 2n states, where n is the number of flip-flops utilized in the counter.

Asynchronous Counter Applications

Asynchronous counters, often known as divide by N counters, are used as frequency dividers. These are utilized for low-power applications and emit less noise. These are utilized in the creation of an asynchronous decade counter.

The Asynchronous counter is also included in the Ring counter and the Johnson counter. Mod N ripple counters employ asynchronous counters. For example, the ripple counters are Mod 3, Mod 4, Mod 8, Mod 14, Mod 10, etc.

Advantages of Asynchronous counter

Asynchronous counters may be simply constructed with Toggle or D-type flip-flops. Because the clock inputs of the flip-flops are not all controlled by the same clock signal, they are referred to as "Asynchronous Counters."

Each output in the chain is dependent on the previous flip-flop's output. Asynchronous counters are sometimes known as ripple-counters because the data seems to "ripple" from one flip-flop’s output to the next input.

Disadvantages of Asynchronous counter

An additional "re-synchronizing" output flip-flop may be needed. Extra feedback circuitry is necessary to count a shortened sequence that is not equal to 2n. When a significant number of bits are counted, the propagation delay via succeeding steps may grow unacceptably long. Because of this delay, they are known as "Propagation Counters."

At high clocking frequencies, counting mistakes arise. Because they use the same clock signal for all flip-flops, synchronous counters are quicker and more dependable.

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FAQs on Asynchronous counter

  • Asynchronous counters have an output that is independent of the clock signal. Because the flip flops in asynchronous counters are provided with distinct clock signals, the output may be delayed. The number of logic gates required to build asynchronous counters is quite small.

  • Asynchronous counters may be constructed with Toggle or D-type flip-flops. Because the clock inputs of the flip-flops are not all controlled by the same clock signal, they are referred to as "Asynchronous Counters."

  • An additional "re-synchronizing" output flip-flop may be needed. Extra feedback circuitry is necessary to count a shortened sequence that is not equal to 2n. When a significant number of bits are counted, the propagation delay via succeeding steps may grow unacceptably long.

  • Asynchronous counters, often known as divide by N counters, are used as frequency dividers. These are utilized for low-power applications and emit less noise. These are utilized in the creation of an asynchronous decade counter.

  • Asynchronous counters are referred to as ripple counters due to the latency in transmitting pulses from flip-flop to flip-flop. Hence, Asynchronous counters are slower than synchronous counters. Asynchronous counters are sometimes known as ripple counters due to the way the clock pulse ripples through the flip-flops.

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