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 all connected to the same clock, resulting in a rippling effect where each flip-flop responds one after the other. In ripple counters, the output of one flip-flop triggers the next flip-flop, and the period of the output doubles with each additional flip-flop.

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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