Synchronous Counters

If all the flip-flops receive the same clock signal, then that counter is called as Synchronous counter. Hence, the outputs of all flip-flops change affect

at the same time.

Now, let us discuss the following two counters one by one.

• Synchronous Binary up counter
• Synchronous Binary down counter

Synchronous Binary Up Counter

An ‘N’ bit Synchronous binary up counter consists of ‘N’ T flip-flops. It counts from 0 to 2^𝑁 − 1. The block diagram of 3-bit Synchronous binary up counter is shown in the following figure.

The 3-bit Synchronous binary up counter contains three T flip-flops & one 2-input AND gate. All these flip-flops are negative edge triggered and the outputs of flip-flops change affect

synchronously. The T inputs of first, second and third flip-flops are 1, Q0 & Q1Q0

respectively.

The output of first T flip-flop toggles for every negative edge of clock signal. The output of second T flip-flop toggles for every negative edge of clock signal if Q0

is 1. The output of third T flip-flop toggles for every negative edge of clock signal if both Q0 & Q1

are 1.

Synchronous Binary Down Counter

An ‘N’ bit Synchronous binary down counter consists of ‘N’ T flip-flops. It counts from 2^𝑁 − 1 to 0. The block diagram of 3-bit Synchronous binary down counter is shown in the following figure.

The 3-bit Synchronous binary down counter contains three T flip-flops & one 2-input AND gate. All these flip-flops are negative edge triggered and the outputs of flip-flops change affect

synchronously. The T inputs of first, second and third flip-flops are 1, Q0′ &' Q1′Q0′

respectively.

The output of first T flip-flop toggles for every negative edge of clock signal. The output of second T flip-flop toggles for every negative edge of clock signal if Q0′

is 1. The output of third T flip-flop toggles for every negative edge of clock signal if both Q1′ & Q0′ are 1.