Synchronous counters use a common clock signal to toggle all flip-flops simultaneously, preventing propagation delay issues seen in asynchronous counters. A synchronous mod-10 (decimal) counter can be built from binary counters by adding logic to reset the count to 0 after reaching 10. This is achieved by detecting the 1001 state and toggling an additional flip-flop on the next clock pulse. Synchronous counters are used in applications like machine motion control and RPM measurement but require more components and complex circuitry compared to asynchronous counters.

2. Synchronous Counter
• Synchronous Counters are so called because the
clock input of all the individual flip-flops within
the counter are all clocked together at the same
time by the same clock signal.
• Asynchronous counter suffers from what is known
as “Propagation Delay” in which the timing signal
is delayed a fraction through each flip-flop.
• In Synchronous counters all the individual output
bits changing state at exactly the same time in
response to the common clock signal with no
ripple effect and therefore, no propagation delay.

3. Synchronous Mod –10 Counter
• A 4-bit decade synchronous counter can also be
built using synchronous binary counters to
produce a count sequence from 0 to 9. A standard
binary counter can be converted to a decade
(decimal 10) counter with the aid of some
additional logic to implement the desired state
sequence.
• After reaching the count of “1001”, the counter
recycles back to “0000”. We now have a decade
or Modulo-10 counter.

4. Circuit Diagram

6. Working Principle
• The additional AND gates detect when the
counting sequence reaches “1001”, (Binary
10) and causes flip-flop FFD to toggle on the
next clock pulse. Flip-flop FFA toggles on
every clock pulse. Thus, the count is reset
and starts over again at “0000” producing a
synchronous decade counter.

7. Applications & Limitations
• Used in Machine Motion control.
• Used in Motor RPM counter.
• Used in Rotary Shaft Encoders.
• Used in digital clock or pulse generators.
• Used in digital Watch and Alarm systems.
• They require large no. of components and
circuitry than asynchronous counters.
• The design involves a complex logic circuit as well
as the increasing no. of states.

8. Thank You