Section 7: TSP command reference
Model 2657A High Power System SourceMeter® Instrument Reference Manual
7-244
2657A-901-01 Rev. B/December 2012
smuX.trigger.source.logY()
This function configures an exponential (geometric) source sweep.
Type
TSP-Link accessible
Affected by
Where saved
Default value
Function
Yes
Usage
smu
X
.trigger.source.log
Y
(
startValue
,
endValue
,
points
,
asymptote
)
X
Source-measure unit (SMU) channel (for example,
smua.trigger.source.logv(1,
10, 11, 0)
applies to SMU channel A)
Y
SMU source function (
v
= voltage,
i
= current)
startValue
Source value of the first point
endValue
Source value of the last point
points
The number of points used to calculate the step size
asymptote
The asymptotic offset value
Details
This function configures the source action to be a geometric source sweep in a subsequent sweep. During the
sweep, the source generates a geometric series of ascending or descending voltage or current changes called
steps. Each step is larger or smaller than the previous step by a fixed proportion. The constant of proportionality
is determined by the starting value, the ending value, the asymptote, and the number of steps in the sweep. The
number of source steps is one less than the number of sourced
points
.
The
points
parameter does not set the number of steps in a sweep, but rather is used to calculate source
values within a subsequent sweep. If the subsequent sweep has more points than specified in
points
, the
source restarts at the beginning. This means that if the trigger count is greater than the number of points in a
sweep as configured, the SMU satisfies the trigger count by restarting the sweep values from the beginning.
If the subsequent sweep has fewer points than specified in
points
,
endValue
is not reached during the sweep.
This means that if the trigger count is less than the number of source values configured, the SMU satisfies the
trigger count and ignores the remaining source values.
In cases where the first sweep point is nonzero, it may be necessary to pre-charge the circuit so that the sweep
returns a stable value for the first measured point without penalizing remaining points in the sweep.
With logarithmic sweeps, it is usually necessary to allow the source to autorange to maintain good source
accuracy when sweeping over more than one decade or across range boundaries.
The
asymptote
parameter can be used to customize the inflection and offset of the source value curve. This
allows log sweeps to cross zero. Setting this parameter to zero provides a conventional logarithmic sweep. The
asymptote
value is the value that the curve has at either positive or negative infinity, depending on the direction
of the sweep.
The
asymptote
value must not be equal to or between the starting and ending values. It must be outside the
range defined by the starting and ending values.
The SMU stores only the most recent configured source action. The last call to
smu
X
.trigger.source.linear
Y
()
,
smu
X
.trigger.source.list
Y
()
, or
smu
X
.trigger.source.log
Y
()
is used for the source action.
Source functions cannot be changed within a sweep.
After configuring the sweep source values, enable the source action by setting
smu
X
.trigger.source.action
.
Example
smua.trigger.source.logv(1, 10, 11, 0)
Sweeps SMU channel A from 1 V
to 10 V in 10 steps with an
asymptote of 0 V.
Summary of Contents for 2657A
Page 3: ......
