Information Technology Reference
In-Depth Information
implement the shifting operation [14]. Afterwards, we show how to extend the first
implementation if a simple shifter to design a p-shifter.
AS
PIN
-
WAVE
S
IMPLE
S
HIFTER
. A simple shifter is a combinational system
having (N+2)-bit data-input, N-bit data output, and two one-bit control inputs: d
(shifter direction) and s (shift or no shift). This system shifts the input data by one
bit either to the right or to the left (depending on the value of d ), or delivers the
input data unchanged [1]. In implementing a simple shifter, we need N+2
processing nodes. Except the first and last nodes which are just input nodes,
The nodes act as both inputs and outputs, except the first and last nodes that are
just inputs. We present two methods for implementing a simple shifter.
In the first method, a single frequency is assigned to each of the nodes. The
receiving frequencies of all nodes are tuned on these distinct frequencies. In
addition, each node is aware of the frequency of its neighboring nodes. Each node
determines its sending frequency based on the control signals. If control signal s
shows ''no shift,'' no node sends out any signal. On the other hand, if s commands
to ''shift,'' each node's sending frequency will be tuned on its right or left
neighbor's frequency depending on the direction shown by control signal d. For
instance, node x
i
sends its data on frequency f
i+1
if d indicates shift to the left and
on f
i
1
for shift to the right. Since these data transmissions are done on different
frequencies, all can be performed simultaneously. The structure of this shifter
(except s and d) is shown in Figure 9.9.
In the second method, all the nodes are tuned on the same frequency, and the
shifting operation is performed by using spin-wave switches. The structure of this
shifter is shown in Figure 9.10. If s indicated ''no shift,'' all the nodes keep their
switches off and no wave is transmitted; otherwise, the shifting operation is
performed by using the spin-wave switches. Note that spin-waves propagate in
both directions in the ferromagnetic bus; however, they can be forced in one
direction by using the spin-wave switches. The structure of spin-wave switches
were described in Chapter 7.
To implement shifting to the right, all the nodes turn off their left switch and
send out a spin-wave with an amplitude equal to their data while their right switch
is open. This forces the waves to be directed to the right. As soon as the nodes send
their waves, they immediately open their left switch and close their right switch.
...
...
...
...
y
n
−
1
y
n
−
2
y
i
x
i
y
0
x
0
x
n
x
n
−
1
x
i
x
0
x
−
1
Outputs:
Inputs:
...
...
x
n
x
n
−
1
x
n
−
2
x
−
1
s
d
S/N-S
L/R
Shifter
Shift right
Shift left
f
n
−
1
f
0
f
n
−
2
f
i
...
...
f
0
f
n
−
1
f
i
f
1
y
n
−
1
y
i
y
0
Figure
9.9.
Structure of a nanoscale spin-wave shifter using multiple frequency
assignments.
Search WWH ::
Custom Search