Beginningthemeasurement - Keithley 595 Instruction Manual

OPERATION
this would be the lowest range that doesn't "overrange" the
inshument. For example, to measure a capacitor with an
approximate value of l.SnF, the 2nF range would give a
higher degree of resolution than the 2OnF range (as long
as the change in capacitance vs. voltage does not cause the
value to exceed 2nJ? and overrange the instrument du+g
the test).
Now that the voltage limits, step size and measurement
range have been determined, it is tie to begin the set of
measurements that will form the curve.
3.8 BEGINNING THE MEASUREMENT
Select the DC waveform to keep the instnunent from begin-
ning the staircase measurement until the appropriate
parameters have been selected. Now, enter the upper and
lower voltage source limits as determined from the spot
check previously performed (in this example, -6.5V is the
lower limit~and -4.W is the upper limit). Also, select the
step size, direction, measurement range and delay time.
NOTE
When setting up measurements such as the IV for
a zoner diode illustrated in this example, delay time
is not a critical parameter due to the nature-of the
device. However, applications involving MOS de-
vices may require that the measurement be suffi-
ciently slow so that the device achieves equilibrium,
in which case delay time becomes critical. This
delay time, which occurs in the inversion region,
is also measurement-direction dependent. If a
measurement is changed to DC, the output voltage
is moved to the next level where the effective step
is off m order to preserve the direction of the
measurement. See Applications, paragraph 5.3.3,
for information on how to select the appropriate
delay time for MOS devices.
Connect the device and turn off ZERO CHECK. TO begin
the measurement, set STEP V to the staircase waveform,
and set the voltage squrce to the starting voltage 1eveI with
either the voltage source ADJUST buttons or PRESET. Final-
ly, select the steps waveform and the measurement staircase
will begi+
To pause the staircase, change the waveform to DC. If
desired, the step direction or voltage source can be adjusted
at this time, then the staircase can be resumed by return-
~. ^--
mg tne wavetonn to x%1'.
Reading rate is a function of delay time. For capacitance
measurements, there are two step times for every reading.
For current measurements, a reading is ready every step
time (delay time +O.C!4sec).
3.9 DIGITAL PLOTTING
The previous paragraphs described how to initiate a stair-
case CV, IV or Q/t-V measurement with the Model 595. Thii
section wilI illustrate how to plot a curve with a digital plot-
ter over the IEEE-488 bus with the Model 595 acting as a
controller.
The following HPGL-compatible (Hewlett Packard
Graphics Language) plotters are some of the types that may
be used with the Model 595 to plot curves: 747OA, 7475A,
755OA, 758OA, 7585A, 75858, 75868. The Model 595 uses
these HPGL commands to communicate with the digital
plotter: IN, IP, SC, PU, PD, PA, IW, LB, SP, and SI. All
numeric values are integers except those used with SI.
1.
2.
3.
4.
Use the following procedure to set up the Model 595 and
the plotter:
Set the waveform to-~ DC and select measurement
parameters as determined by the previous paragraphs.
@?I+ the plotter to the bus connector of the Model
595 and set the plottefs IEEE-488 address to 5. Then
power up the plotter (NOTE: some plotters only read
the address switch on power up). Make sure that Pen
#i is iti the holder.
Now set the Model 595's IEEE-488 code to 42 or 43 from
the front panel IEEE address program. This enables the
Model 595 to control the plotter. Select code 42 for a
standard plot (voltage on the X axis, running from the
Lo limit (left) to the HI limit) or select code 43 to "flip'
the X axis (so that voltage runs from the HI limit to the
LQ limit). Since the voltage source output is usually ap-
plied to the substrate of a MOS capacitor, the gates
voltage is effectively the negative of the voltage source
output. Code 43 allows the shape of the plot to resem-
ble the usual Capacitance vs. Gate Voltage Curve. (See
Appendix for a description of data and control strings
sent to the plotter).
Choose Y HI and Y LO values if desired from the front
panel programs as descriied in paragraph 3.4.10 to maxi-
mize plot resolution on the Y axis.
3-16