A ring counter is a type of digital counter circuit that consists of a series of flip-flops (also known as bistable multivibrators) connected in a circular or ring configuration. The ring counter is designed to generate a cyclic sequence of binary states, where only one flip-flop is active at a time while the others remain inactive. The active flip-flop effectively acts as a "1" bit, while the inactive ones act as "0" bits.
The operation of a ring counter involves propagating the active state through the flip-flops in a continuous loop, creating a circular shift of the "1" bit. This cyclic sequencing is achieved by connecting the output of each flip-flop to the input of the next flip-flop in the sequence, with the final flip-flop's output looped back to the first flip-flop's input.
Here's a simple example to illustrate the concept of a 4-bit ring counter:
Initially, all flip-flops are set to the same value (either all "0" or all "1").
On the clock signal's rising edge (or falling edge, depending on the specific design), the active state (the "1" bit) moves one position to the right.
This shifting action continues with each clock pulse, and after each complete cycle, the active state has moved through all the flip-flops and returned to its original position.
The key feature of a ring counter is that only one flip-flop is active at any given time, creating a cyclic sequence of states. This can be useful in various applications such as digital clocks, frequency dividers, and control logic circuits.
It's important to note that a ring counter can suffer from the "race" condition, where multiple flip-flops may briefly be in an active state at the same time during the transition from one state to another. To avoid this issue, additional logic elements, like gates or synchronization signals, may be added to ensure proper operation and to suppress any unwanted glitches in the sequence.