Table of Contents
Advertisement
Operation
Figure
4-9
Common-emitter
characteristics
of
an
NPN
silicon
Transistor
4.5
Measurement
considerations
sideration;
however,
it
can
seriously
degrade
measurement
accuracy
when
testing
high-impedance
devices.
The
voltage
measured
across
such a
device, for
example,
can be
substantially
attenuated
by
the
volt-
age
divider action of the device source resistance
and
path
isolation resistance,
as
shown
in
Figure
4-11.
Also,
leakage currents can
be
generated through
these
resis-
tances
by
voltage sources
in the
system.
Rout
-
Source
Resistance
of
OUT
Edut
=
Source
EMF
of
DUT
Rpath
=
Path
Isolation
Resistance
RiN
=
input
Resistance
of
Measuring
instrument
Many
measurements
made
with
the
Model
7012
are
subject
to
various
effects
that
can
seriously
affect
low-
level
measurement
accuracy.
The
following para-
graphs
discuss these
effects
and ways
to
rninimize
them.
Figure
4-10
Path
isolation resistance
4.5.1
Path
isolation
The
path
isolation
is
simply
the equivalent
impedance
between any two
test
paths
in
a
measurement
system.
Ideally,
the
path
isolation
should be
infinite,
but
the
ac-
tual resistance
and
distributed
capacitance of cables
and
connectors
results in less
than
infinite
path
isola-
tion
values
for
these devices.
IDUT
EoUT =
Edut
Rpath
Rout
+
Rpath
Path
isolation resistance
forms a
signal
path
that
is
in
Figure 4-11
parallel
with
the equivalent resistance of the
DUT,
as
Voltage attenuation
by
path
isolation
resistance
shown
in
Figure
4-10.
For
low-to-medium
device
resis-
tance
values,
path
isolation
resistance
is
seldom
a con-
4-13
Advertisement
Table of Contents
