  The switching time of a magnet in a spin current based majority gate depends
on the input vector combination, and this often restricts the speed of
majority-based circuits. To address this issue, this work proposes a novel
two-phase scheme to implement majority logic and evaluates it on an all-spin
logic (ASL) majority-based logic structures. In Phase 1, the output is
initialized to a preset value. Next in Phase 2, the inputs are evaluated to
switch the output magnet to its correct value. The time window for the output
to switch in Phase 2 is fixed. Using such a scheme, an n-input AND gate which
requires a total of (2n-1) inputs in the conventional implementation can now be
implemented with only (n+1) inputs. When applied to standard logic functions,
it is demonstrated that the proposed method of designing ASL gates are 1.6-3.4X
faster and 1.9-6.9X more energy-efficient than the conventional method, and for
a five-magnet full adder, it is shown that the proposed ASL implementation is
1.5X faster, 2.2X more energy-efficient, and provides a 16% improvement in
area.
