NANOSCALE STANDARD DIGITAL MODULES - Bio-Inspired and Nanoscale Integrated Computing - page 244

The architectures presented here use spin waves for information transmission
and data processing. Spin wave is a collective oscillation of spins in an ordered
spin lattice around the direction of magnetization [2]. A propagating spin wave
changes the local polarization of spins in ferromagnetic material. In turn, the
change in magnetic field results in an inductive voltage. Recent published
experimental results indicate that an inductive voltage signal of the order of mV
produced by spin waves propagating through a nanometer thin ferromagnetic film
are detectable at the distances of up to 50 microns at room temperature [3, 4].
A number of spin-wave architectures have been recently proposed, namely, logic
gates [5-7], a crossbar [8, 9], a reconfigurable mesh [10, 11], and a fully interconnected
cluster [12]. Similar to those architectures, in the spin-wave digital modules presented
here, information is encoded into the phase of the spin waves. Moreover, all these
architectures are capable of transmitting multiple waves simultaneously.
In this chapter, we present a set of widely used digital architectures and
demonstrate how they can be implemented at the nanoscale [13]. A number of
these standard and combinational arithmetic and logic modules, including full
adders, multipliers, logic gates, decoders, encoders, multiplexers, and demultiplex-
ers can be implemented by employing the concurrent write and superposition
property of the spin waves. To implement more complex modules such as priority
encoders and shifters, spin-wave switches [8] are used as well.
The rest of this chapter is organized as follows: In Section 9.2, we present our
proposed spin-wave combinational arithmetic modules. We then describe the
proposed spin-wave standard combinational logic modules in Section 9.3. We
present more complex digital modules in Section 9.4, followed by our conclusion
and future work in Section 9.5.

9.2. NANOSCALE SPIN-WAVE STANDARD ARITHMETIC MODULES

In this section, we first present a digital to analog module that is used in the design
of several other arithmetic and logic modules. Afterwards, we show how to
implement spin-wave full adders and multipliers.

9.2.1. Nanoscale Spin-Wave Digital to Analog Converter
As mentioned in Chapter 7, the computation using spin waves can be done in both
digital and analog forms. We assume that upon receiving an analog signal, analog
to digital conversion is performed in each processing node by comparing the signal
value to several threshold voltages. In this section, we illustrate a simple method
for converting a digital value to an analog signal to be transmitted via the spin-
wave bus. The analog value is computed as the weighted sum of input bits, where
the weight of the ith value is 2 i .

Analog value ¼ X

N 1

i 2 i

i ¼ 0