Keithley 237

Source
Value
jE"Delay~
!E"Oelay~
~Delay~
l l
r~o..,
......
~Delay~
+
Measure
Measure Measure
Measure Measure
Point 1
Point2 Point3
Point4
Point5
Time
Sweep Waveform
Figure
1-5.
Example
Sweep
''Elapsed
time"
time stamps each measurement of
the
sweep. Each elapsed time
is
measured from the begin-
ning of the sweep to the
end
of the measurement for each
point. Notice that
in
addition to the programmed delay,
there is time contributed
by
other factors, such as the inte-
gration time
of
the measurement. The time stamps are
useful
when
performing
V
or
I versus t tests.
When RECALL is enabled, the
data
in
the sweep buffer is
displayed
by
the Source Measure
Unit
using the rotary
knob
and
the
SELECT
buttons. The display serves as a
"window"
to view each
data
parameter. As
shown
in
the
illustration, the rotary knob moves the display "win-
dow" vertically, while the
SELECT buttons move the dis-
play "window"
horizontally.
1.3
BASIC CIRCUIT CONFIGURATIONS
The simple models
shown
in
Figure
1-1
have been ex-
panded
to include the driven
guard
and
sense circuits,
and
are
shown
in
Figure 1-6
and
Figure 1-7.
Source I Measure
V
To Source I Measure
V
(see Figure 1-6), a voltmeter
(VMETER)
is connected
in
parallel
with
the current source
(!soURCE).
In this configuration, the Source
Measure
Unit
will function as a high-impedance current source
with
voltage measure (and limit) capability.
+
+
Point
Ol
1
2
3
Rotary
4
5
Knob
<]
SELECT
[>
SECTION1
Getting
Started
Source
Delay
Measure
Elapsed
Time
1.00V 1s 2m A
1.002s
3.00V
1s 6mA
2.003s
5.00V
1s 10mA
3.004s
3.00V 1s 6mA
4.005s
1.00V
2s 2mA
6.006s
Sweep Buffer
Contents
Sense
selection (local
or
remote) determines where the
voltage measurement is made.
In
local sense, voltage is
measured
at
the
output
of the
Source
Measure
Unit.
In
re-
mote sense, voltage is measured
at
the DUT eliminating
any voltage
drops
that
may
be
in
the test leads
or
connec-
tions between the
Source Measure
Unit
and
the DUT.
The driven
guard
needed to accurately source
low
cur-
rent is provided
by
a buffer circuit. The
X1
buffer ensures
that
GUARD
and
OUTPUT
HI
always remain
at
the same
potential. Proper
use
of GUARD virtually eliminates
leakage
paths
in
the cable, test fixture
and
connectors.
Source
V
Measure I
To Source
V
Measure I (see Figure 1-7),
an
ammeter
(~METER)
is connected between the voltage source
(VsoURcE)
and
OUTPUT
HI.
In
this configuration, the Source Meas-
ure
Unit
will
function as a low-impedance voltage source
with
current measure (and limit) capability.
Sense
circuitry
is
used
to constantly monitor the
output
voltage
and
make adjustments to
VSOURCE
as needed.
VMETER
measures the voltage
at
the
output
(local sense)
or
at
the DUT (remote sense)
and
compares
it
to
the
pro-
grammed voltage level.
If
the sensed (measured) level
and
the
programmed
value are
not
the same,
V
soURCE
is
adjusted accordingly.
Here
again, remote sense elimi-
nates the effect of voltage
drops
in
the test leads ensuring
that
the exact
programmed
voltage appears
at
the DUT.
The driven
guard
needed
to accurately measure
low
cur-
rent is
provided
by
the
X1
buffer circuit.
GUARD
and
OUTPUT
HI
will always
be
at
the same potential.
1-7