A shift register with its complement output (Q’) of the last sta...
Ring counter:
The Ring shift counter is a recirculating register in which the serial output is connected back to the serial input as shown:

A Straight ring counter with ‘n’ flip-flops will have n states.
Johnson counter:
A Johnson counter is a modified ring counter, where the inverted output from the last flip flop is connected to the input to the first.
It is also called a twisted ring counter.
The MOD of the Johnson counter is 2n if n flip-flops are used.
The circuit diagram for a 4-bit Johnson Counter is as shown:
A shift register with its complement output (Q’) of the last sta...
Understanding Twisted-Ring Counter
A twisted-ring counter is a specific type of shift register configuration where the complement output of the last flip-flop stage is fed back into the first stage. This creates a unique behavior in the counting mechanism.
Key Features of Twisted-Ring Counter
- Feedback Mechanism: The last stage’s complement output (Q') is connected to the D-input of the first stage, which allows for a modified counting sequence.
- Counting Sequence: The feedback creates a pattern of binary counting that is not linear, resulting in a series of states that represent a cycle.
- State Representation: For an n-stage twisted-ring counter, there are 2^n possible states, but only n states are used in practice. This is because the nature of the feedback limits the number of valid states.
Applications of Twisted-Ring Counters
- Digital Circuit Design: Twisted-ring counters are commonly used in digital circuits for generating specific sequences, such as in sequence detectors or state machines.
- Synchronous Operation: Since all flip-flops in a twisted-ring counter can be clocked simultaneously, they operate in a synchronous manner, enhancing the stability and performance of the circuit.
Comparison with Other Counters
- Synchronous Counter: Unlike a twisted-ring counter, a synchronous counter counts in a straightforward binary manner without the unique feedback characteristic.
- Asynchronous Counter: An asynchronous counter does not have a direct feedback mechanism and relies on the propagation of clock signals, which can lead to delays.
Conclusion
Thus, the unique feedback mechanism and the resultant counting sequence characterize the twisted-ring counter, making it a distinct and valuable component in digital electronics.