Johnson vs. Ring Counter: Period and State Comparison
A 4-bit shift register forms a Ring counter when its last bit Q3 feeds back directly to Q0, and a Johnson counter when the inverted last bit feeds back to Q0.
Three signals are shown: CLK (clock, period 2), QR0 (Ring counter output bit 0), and QJ0 (Johnson counter output bit 0). Both circuits are positive-edge-triggered and shift right from Q0 to Q3. The Ring counter begins in state 1000 (meaning QR0 is initially 1 and all other bits are 0), while the Johnson counter begins in state 0000.
Trace QR0 and QJ0 across all 16 time steps.
Constraints
- Both shift registers evaluate the value at
Q3immediately prior to the rising clock edge to determine the next value ofQ0. - Output transitions occur only on the LOW-to-HIGH edge of
CLK. - State shifts strictly from index 0 toward index 3.
Topics
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