Distinguishing a ring shift counter from a Johnson (twisted-ring) counter What is the key difference between a ring counter and a Johnson counter?

Introduction / Context:
Both ring and Johnson counters are built from shift registers with feedback, but their feedback polarity changes the sequence of states, the number of states, and common use cases. Correctly identifying the feedback difference is essential to predicting sequences and designing decoders.

Given Data / Assumptions:

• Ring counter: last stage output fed directly (non-inverted) back to the first stage.
• Johnson counter: last stage output is inverted before being fed back to the first stage.
• Both are clocked synchronously.

Concept / Approach:
With non-inverted feedback, a ring counter simply circulates a single 1 (or 0), producing N states from N flip-flops (one-hot). With inverted feedback, a Johnson counter produces 2N states by toggling runs of 1s and 0s, which are convenient for evenly distributed decoded outputs.

Step-by-Step Solution:
Identify feedback path: ring → direct; Johnson → inverted.Relate to number of states: ring → N; Johnson → 2N.Therefore, the distinguishing feature is inverted feedback in the Johnson counter.

Verification / Alternative check:
Enumerating states for a 4-bit example: ring → 4 states; Johnson → 8 states. Textbook sequences confirm the feedback polarity difference.

Why Other Options Are Wrong:

• “No difference” is incorrect; the feedback polarity is fundamental.
• Speed claims (always faster) are context-dependent and not a defining difference.

Common Pitfalls:

• Confusing Johnson with ring due to similar shift-register structures.
• Forgetting that Johnson counters are sometimes called twisted-ring counters precisely because of the inverted feedback.

Final Answer:
The feedback is inverted in the Johnson counter, non-inverted in the ring counter