Counters are sequential circuits where the output value increases by one on each clock cycle and wraps around back to zero after reaching the maximum value. Ripple counters are asynchronous counters where the flip-flops are not connected to a common clock, but instead are triggered one after another by each previous flip-flop's output in a ripple effect. This causes the periods of each successive flip-flop to be multiples of the clock period, with the last flip-flop having the largest period of 2n for an n-bit ripple counter.

1. Counters
• Counters are a specific type of
sequential circuit.
• Like registers, the state, or the flip-
flop values themselves, serves as the
“output.”
• The output value increases by one on
each clock cycle.
• After the largest value, the output
“wraps around” back to 0.
1

2. Using two bits:
1
00 01
Present State Next State
A B A B
0 0 0 1 1 1
0 1 1 0
1 0 1 1
1
1 1 0 0
11 10
2

3. RIPPLE COUNTER
(ASYNCHRONOUS COUNTER)
3

4. Asynchronous Counters
• This counter is
called asynchronous
because not all flip
flops are hooked to
the same clock.
4

5. • This is called as a ripple
counter due to the way the FFs
respond one after another in a
kind of rippling effect.
• In a ripple counter, a flip-flop
output transition serves as a
source for triggering other flip-
flops. 5

6. 6

7. Asynchronous counters
If the clock has period T.
Q0 has period 2T. Q1
period is 4T
With n flip flops the period
is 2n.
7

8. • Binary Ripple Counter
–(2 bits, 3 bits, 4 bits, …)
– 1 to 0
• Binary Countdown Counter
– 0 to 1
• BCD Ripple Counter
–4 bits
8

9. 9

10. BINARY RIPPLE COUNTER
10

11. BINARY COUNTDOWN COUNTER
11

12. 12

13. BCD RIPPLE COUNTER
13

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