Abstract
The key enabling factor for Spin Wave (SW) technology utilization for
building ultra low power circuits is the ability to energy efficiently
cascade SW basic computation blocks. SW Majority gates, which constitute
a universal gate set for this paradigm, operating on phase encoded data
are not input output coherent in terms of SW amplitude, and as such,
their cascading requires information representation conversion from SW
to voltage and back, which is by no means energy effective. In this
paper, a novel conversion free SW gate cascading scheme is proposed that
achieves SW amplitude normalization by means of a directional coupler.
After introducing the normalization concept, we utilize it in the
implementation of three simple circuits and, to demonstrate its bigger
scale potential, of a 2-bit inputs SW multiplier. The proposed
structures are validated by means of the Object Oriented Micromagnetic
Framework (OOMMF) and GPU-accelerated Micromagnetics (MuMax3).
Furthermore, we assess the normalization induced energy overhead and
demonstrate that the proposed approach consumes 20% to 33% less energy
when compared with the transducers based conventional counterpart.
Finally, we introduce a normalization based SW 2-bit inputs multiplier
design and compare it with functionally equivalent SW transducer based
and 16nm CMOS designs. Our evaluation indicate that the proposed
approach provided 26% and 6.25x energy reductions when compared with
the conventional approach and 16nm CMOS counterpart, respectively, which
demonstrates that our proposal is energy effective and opens the road
towards the full utilization of the SW paradigm potential and the
development of SW only circuits.