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OPERATION
2.4.1 Single-Ended
Switching
same potential
as signal high, protection
from possible
hazardous voltages (up to 2ooV) must be provided.
Many
In the single-ended
switching
configuration,
the source or
instruments
have the capability
of configuring
their input
measure instrument
is connected to the DUT through
a
or output such that a driven guard is placed on the inner
single pathway as
shown
in Figure 2-4. Note that in the
shield of a triax connector. The outer shield, connected to
illustration
that the matrix card guard (G) is used as a
system common,
provides
protection
from the guard
shield. The matrix card guard is used as the shield because
voltage. When making connections
from the matrix card
its PC board trace physically
surrounds
the high (H) and
to the DUT, make sure that a safety shield is used as shown
low (L) traces.
in the illustration.
2.4.2 Differential
Switching
2.4.4 Sensing
The differential
or floating
switching
configuration
is
Figure 2-7 shows how the matrix card can be configured
shown in Figure 2-5. The advantage of using this configura-
to use instruments
that have sensing capability.
The main
tion is that the terminals of the source or measure instru-
advantage of using sensing is to cancel the effects of matrix
ment are not confined to the same matrix crosspoint. Each
card path resistance (< 1.5II) and the resistance of exter-
terminal of the instrument
can be connected to any of the
nal cabling. Whenever path resistance is a consideration,
96 matrix crosspoints.
Again, the guard terminals
of the
sensing should be used. In the illustration,
matrix card
matrix card are used as a shield.
guard is again used as a shield. In a system whew a driven
guard is required,
matrix card guard (G) can be discon-
nected from circuit LO and connected to the guard poten-
2.4.3 Guarding
tial. However, make sure that the guard is adequately in-
sulated to prevent possible electrical shock, or use quadrax
Figure 2-6 shows how the matrix card can be used with
cables using the outer shield as a grounded
safety shield.
a driven guard. Since the driven guard is at virtually
the
Shield
Figure 2-4. Single-Ended
Switching
Example (Guard Used as Shield)
2-6
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