When the output of a flip flop is used as the clock input for the next flip flop, the counter is called 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.
It is simple and easy to construct.
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.
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