prin
ted
circuit
b
oards
to
a
v
oid
ground
lo
ops
crosstalk
oscillation
and
other
e ects
A
solution
to
suc
h
a
problem
is
to
design
a
device
that
could
b
e
more
fully
digital
p
ossibly
tting
mostly
in
to
one
application sp
eci c
IC
or
eld programmable
gate
arra
y
Suc
h
a
solution
could
b
e
attained
b
y
dev
eloping
a
miniature
time of igh
t
range nder
The
time of igh
t
range nder
relies
on
a
simple
principle
measure
the
time
it
tak
es
a
short
pulse
of
laser
ligh
t
to
lea
v
e
the
device
hit
an
ob
ject
and
return
Most
of
the
hardw
are
could
b
e
dev
elop
ed
in
an
FPGA
All
that
is
otherwise
needed
is
a
high gain
photo
dio
de
receiv
er
and
a
laser
pulser
The
laser
pulser
can
simply
b
e
a
logic
line
pulsing
a
fast
driv
er
suc
h
as
the
one
w
e
already
ha
v
e
The
receiv
er
can
also
b
e
similar
to
what
exists
in
our
curren
t
circuit
with
the
simple
addition
of
a
high pass
lter
and
digital
discriminator
after
the
fron
t
end
ampli er
The
only
problem
that
exists
is
that
of
resolution
Since
ligh
t
tra
v
els
at
x
m s
in
order
to
measure
with
an
accuracy
of
one
meter
y
ou
need
to
clo
c
k
the
coun
ter
with
a
Mhz
input the
divide b
y t
w
o
comes
from
the
path
bac
k
as
w
ell
as
to
the
ob
ject
measuring
a
meter
in
range
requires
a
tra
v
el
of
t
w
o
meters
If
one
w
an
ted
to
clo
c
k
with
cen
timeter
resolution
the
clo
c
k
rate
rises
to
times
that
frequency
whic
h
ma
y
b
e
somewhat
unreasonable
Man
y
systems
that
use
this
tec
hnique
emplo
y
t
w
o
phase lo
c
k
ed
clo
c
ks
th
us
reducing
the
n
um
b
er
of
bits
necessary
for
the
fast
clo
c
k BS
Y
ou
can
then
use
the
coarse
clo
c
k
for
lo
w
er
resolution
and
then
add
the
coun
ts
of
the
ne
clo
c
k
Other
systems
use
a
simple
time stretc
her
circuit VKY
quic
kly
c
harging
a
capacitor
during
the
in
terv
al
to
b
e
measured
then
timing
ho
w
long
it
tak
es
it
to
b
e
fully
disc
harged
at
a
m
uc
h
lo
w
er
curren
t
hence
longer
in
terv
al
These
o
v
erall
metho
ds
are
simple
but
mostly
require
v
ery
fast
logic
Suc
h
TOF
systems
are
most
often
used
in
cases
w
ere
higher
precision
isn t
necessary
e g
in
military
ri e
sigh
ts Urb
or
spacecraft
remote
sensing Col
Microscanners
The
next
impro
v
emen
t
that
could
b
e
addressed
is
that
of
the
scanning
and
optical
assem
blies
They
can
easily
b
e
made
m
uc
h
smaller
There
are
t
w
o
lev
els
of
minia