Differential Conductance; Model 622X Measurement Process - Keithley 6220 DC User Manual

5-34 Delta, Pulse Delta, and Differential Conductance
3. When using a Fixed output, use the SOUR:PDEL:INT command to set the
Pulse Delta cycle time period (in PLCs).
When using Sweep output, use the SOUR:DEL command to set the Pulse
Delta cycle time period (in seconds) for a linear or log sweep. For a custom
sweep, use the SOUR:LIST:DEL command to cycle time (in seconds). See
Section 4
4. When using a Fixed output, use the SOUR:PDEL:RANG command to set the
source range. When using a Sweep output, use the SOUR:SWE:RANG com-
mand to set range.
5. After setting up Pulse Delta using the setup commands, the :ARM command
arms Pulse Delta. During the arming process, the Model 622x communicates
with the Model 2182A.
When armed, Pulse Delta will start when the Model 6221 is triggered. Pulse
Delta can be "un-armed" by sending the following command:
SOURce:SWEep:ABORt.
The query form for the arm command (SOUR:PDEL:ARM?) is used to deter-
mine if Pulse Delta is armed. A returned "1" indicates that Pulse Delta is
armed. A "0" indicates that Pulse Delta is not armed.
If the Model 6221 is already armed for another action (e.g., Differential Con-
ductance or Delta), the Pulse Delta arm command will "un-arm" the other
action and arm Pulse Delta.

Differential Conductance

Differential measurements can be used to study the individual slopes of an I-V (or
V-I) curve. By applying a known differential current (dI) to a device, differential
voltage (dV) measurements can be performed. With dI and dV known, differential
conductance (dG) and differential resistance (dR) can be calculated.

Model 622x measurement process

This measurement process is used to eliminate the effects of thermal EMFs, and
a 3-point moving average calculation algorithm is used to provide more accurate
readings.
The differential measurement process is shown in
configured to output a stepped sweep with a specified Delta, which is the differen-
tial current (dI). As shown in the illustration, Delta is added to and subtracted from
each subsequent step in the sweep. The solid line is the actual output of the
Model 622x.
As shown, each differential voltage calculation (dV Calc) uses the three previous
Model 2182/2182A A/D measurement conversions. Keep in mind that dI (Delta) is
the same for all calc points. With dI known and dV calculated, the Model 622x can
for details on sweeps.
Return to Section 5 topics
Model 6220/6221 User's Manual
Figure 5-10. The Model 622x is