<s>
An	O
optical	B-Device
trackpad	I-Device
is	O
an	O
input	B-Device
device	I-Device
based	O
on	O
an	O
optical	O
sensor	O
,	O
which	O
detects	O
the	O
displacement	O
of	O
a	O
finger	O
that	O
is	O
moving	O
on	O
top	O
of	O
it	O
.	O
</s>
<s>
The	O
sensor	O
is	O
used	O
typically	O
in	O
smartphones	B-Application
,	O
where	O
it	O
replaces	O
the	O
D-pad	B-Device
,	O
and	O
in	O
ultra-portable	B-Device
or	O
ultra-mobile	B-Device
PCs	I-Device
,	O
where	O
it	O
replaces	O
touchpads	B-Application
,	O
pointing	B-Device
sticks	I-Device
or	O
trackballs	B-Device
as	O
pointing	O
device	O
.	O
</s>
<s>
The	O
main	O
advantages	O
over	O
a	O
D-pad	B-Device
are	O
:	O
</s>
<s>
In	O
comparison	O
with	O
touchpads	B-Application
,	O
it	O
detects	O
actual	O
skin	O
displacement	O
,	O
instead	O
of	O
displacement	O
of	O
the	O
center	O
of	O
the	O
area	O
being	O
touched	O
,	O
and	O
more	O
similar	O
to	O
pointing	B-Device
sticks	I-Device
or	O
compact	O
trackballs	B-Device
by	O
using	O
experience	O
,	O
but	O
with	O
less	O
physical	O
feedback	O
.	O
</s>
