HP 8340A Service Manual page 302

As shown in Figure 8E-l,
PLANE exists between the two innermost and two outermost
Motherboard printed circuit layers.
disperse any digital noise into the GND PLANES and act as an
electrostatic shield between the digital and analog signal
traces. The GND PLANES extend to each. edge of the Motherboard and
are connected to STAR GND.
analog and digital grounds is maximized and signal crosstalk
minimized.
REFERENCE GND - This ground is connected to STAR GND and is
�
used as a low current reference for integrated circuits,
cable shields,
MISCELLANEOUS GROUND PLANES
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A. The ground plane under the 20/30 Loops' aluminum casting
completes a radio frequency interference
comprised of the casting,
loops' ground plane.
GND via a GND trace,
-casting.
Under the M/N Loop's aluminum casting is a ground plane
B.
which connects to STAR GND and is used as an RFI shield.
CHASSIS GND - All grounds and ground planes are mechanically
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secured to the
perimeter and at various other places on the A62 Motherboard.
Model 8340A - Service
A62 Motherboard Cross Section,
With this scheme,
etc. where a very clean reference is desired.
assembly covers,
This ground plane is connected to STAR
and to chassis GND through the aluminum
8340A chassis (CHASSIS GND)
Scans by HB9HCA and HB9FSX
These layers were designed to
isolation between
(RFI) "box"
and the 20/30
around the
the GND
8-391/8-392