to
b
e
maximized pro
viding
an
additional
dB
of
gain
The
MAX
is
follo
w
ed
b
y
t
w
o
Linear
T
ec
hnology s
L
T
MHz
curren
t feedbac
k
ampli ers
They
are
used
as
lo
w gain
cable
driv
ers
in
actualit
y
eac
h
pro
vides
an
additional
dB
of
gain
then
reduced
b
y
a
factor
of
from
cable
matc
hing
A
BNC
cable
follo
ws
this
stage
and
connects
to
the
rac
k
unit
demo
dulator
The
signal
follo
wing
the
last
stage
is
w
ell conditioned
and
stable
enough
to
b
e
fed
directly
in
to
the
demo
dulator
As
the
gain
of
b
oth
b
oards
and
photo
dio
de
together
approac
hes
dB
it
w
as
imp
or
tan
t
to
appropriately
shield
the
b
oards
and
tak
e
considerable
la
y
out
e ort
to
prev
en
t
the
laser
mo
dulation
from
con
taminating
the
photo
dio
de
signal
The
b
oards
eac
h
ha
v
e
top
and
b
ottom
ground
planes
The
alumin
um
moun
t
is
also
grounded
The
op
enings
of
the
housing
are
co
v
ered
b
y
copp
er
plates
The
p
erformance
of
this
unit
w
as
optimized
in
the
second
protot
yp
e
b
y
incorp
orating
lessons
learned
from
the
rst
protot
yp
e
in
to
the
PCB
b
oard
la
y
outs
Laser
Driv
er
The
laser
driv
er
b
oard
w
as
also
attac
hed
to
the
main
scanning
assem
bly
It
is
housed
in
its
o
wn
oating
shielded
b
o
x
isolating
it
from
the
receiv
e
electronics
It
con
tains
a
line
receiv
er
for
the
MHz
clo
c
k
signal
The
output
of
this
receiv
er
is
connected
to
the
gate
of
a
fast
Sup
ertex
VN
MOSFET
The
drain
of
the
MOSFET
is
wired
to
a
resistor
put
in
series
with
the
laser
dio
de
used
to
limit
the
driv
e
curren
t
A
mW
visible
laser
dio
de
is
used
F
or
v
arious
tests
dep
ending
on
the
a
v
ailabilit
y
and
cost
a
range
of
w
a
v
elengths
w
ere
used
v
arying
from
nm
The
laser
w
as
to
b
e
driv
en
at
ab
out
mA
a
v
eraged
curren
t
as
the
laser
is
to
b
e
mo
dulated
with
a
dut
y
cycle
the
p
eak
curren
t
can
b
e
higher
than
the
recommended
setting
The
ano
de
of
the
laser
dio
de
is
connected
to
the
laser
p
o
w
er
connection
of
the
b
oard
The
p
o
w
er
source
for
the
laser
dio
de
can
b
e
switc
hed
on
the
rac
k
unit
It
can
b
e
a
constan
t
v
olts
or
a
serv
o
ed
v
oltage
that
is
a
function
of
the
demo
dulated
receiv
e
signals
the
maxim
um
of
jI
j
and
jQj
This
allo
ws
the
p
o
w
er
of
the
laser
to
decrease
with
re ected
in
tensit
y
e g
increasing
the
measuremen
ts
range
b
y
not
saturating
the
fron
t
end
ampli er
stage
when
an
ob
ject
is
close
to
the
scanner
and
a
v
oiding
ey
e