HP 8340b - Page 213

As
shown
in
Figure
E-1,
analog
and
digital
trace layers
are
separated
by
ground
plane
layers.
These
layers
were
designed to disperse
any
digital
noise
into
the
ground planes
and act
as an
electrostatic
shield
between
the
digital
and
analog
signal
traces.
The
ground
planes
extend to each
edge
of the
motherboard and
are
connected
to
STAR
GND.
This
provides
isolation
between
analog
and
digital
grounds
while
reducing
signal
crosstalk.
•
REFERENCE
GND
—
is
connected
to
STAR
GND
and
is
used
as
a
very
stable
low
current refer¬
ence
for
integrated
circuits
and cable
shields.
•
MISCELLANEOUS GROUND
PLANES:
A.
The
ground plane
under
the
20/30
Loops'
aluminum
casting completes
a
radio
frequency
interference
(RFI)
"box"
comprised
of the
casting, assembly
covers,
and
the
20/30
loops'
ground
plane.
This
ground
plane
is
connected
to
STAR
GND
via
a
GND
trace,
and
to
chassis
GND
through
the
aluminum
casting.
B.
A
ground plane under
the M/N
Loop's aluminum casting
connects
to
STAR GND
and
is
used
as an
RFI
shield.
•
CHASSIS GND
—
All
grounds
and
ground
planes are
mechanically
secured
to the
chassis
(CHAS¬
SIS
GND)
around
the
instrument's
perimeter
and
to
various
other parts
of the
A62
motherboard.
MOTHERBOARD
REPLACEMENT
The
A62
motherboard
is
not
customer/field
replaceable.
Direct
any
questions
concerning mother¬
board
replacement
to
your nearest
HP
service center
for
more
specific instructions.
Refer
to
the
HP
service
center
listing
at
the
end
of
this
manual.
E-2
A62
Motherboard Overall Descriptfon
HP
8340B/41B