Date: 16 Jul 2013

When the output of a flip flop is used as the clock input for the next flip flop, the counter is called ripple counter.

Binary Ripple Counter

A binary ripple counter can be constructed by use of clocked JK flip flops. JK flip flops connected in cascade. The system clock, a square wave, drives flip flop A. The output of A drives B, and the output of B drives flip flop C. All the J and K inputs are tied to +Vcc. This means that each flip flop will change state with a negative transition at its clock input.

The A flip flop must change states before it can trigger the flip flop B which in turn has to change states before it can trigger the C flip flop.

Let us assume that the flip flops are initially reset to produce 0 outputs. If we consider A to be the least significant bit (LSB) and C the most significant bit (MSB) then we can say the contents of the counter is CBA = 000.

Every time there is a negative clock transition, flip flop A will change states. Thus at point ‘a’ on the time line, A goes high, at point ‘b’ it goes back low, at ‘c’ it goes back high and so on.

As A acts as the clock for B, each time the wave form at A goes low, flip flop B will toggle. Thus at point ‘b’ on that time line, B goes high. It then goes low at point ‘d’ and toggles back high again at point ‘f’. Note that the wave form at the output of the flip flop B is one half the frequency of A and one fourth the clock frequency.

Clock Transitions	C	B	A
0	0	0	0
1	0	0	1
2	0	1	0
3	0	1	1
4	1	0	0
5	1	0	1
6	1	1	0
7	1	1	1
0	0	0	0

Since B acts as a clock for C, each time the wave form at B goes low, flip flop C will toggle. Thus C goes high at point ‘d’ on the time line and goes back low again at point ‘h’. The frequency of the wave form at C is one half that at B, but it is only one-eighth the clock frequency.

Advantage of ripple counter

It is simple and easy to construct.

Disadvantages of ripple counter

It is slow as the rippling of the count pulses limit the speed.
It can follow only a straight binary code. So, code converter is required to get different count sequence code.