Section 4: Source-measure considerations
Model 2450 Interactive SourceMeter® Instrument Reference Manual
4-22
2450-901-01 Rev. B/September 2013
Using SCPI commands:
Send the command:
:SOURce:CURRent:HIGH:CAPacitance ON
To turn on high capacitance for a voltage source, replace
CURRent
with
VOLTage
.
Using TSP commands:
Set the source function, then send the command:
smu.source.highc = smu.ON
Charging the capacitor and making readings
The following steps outline the procedure to charge and read a capacitor in high-capacitance mode:
1. Set the current limit to a value that is higher than will be used for the measurement (for example,
if measuring at 10
µ
A, the initial current limit can be set for 1 A).
2. After the capacitor charges, lower the current limit and measure range to obtain the current
measurement.
Filtering measurement data
Filters allow you to produce one averaged sample from a number of measurements. In situations
where you have noise levels that fluctuate above and below the measured signal, this can help you
produce more accurate measurements.
The Model 2450 has two filter options, repeating average and moving average.
The repeating average filter produces slower results, but produces more stable results than the
moving average filter. For either method, the greater the number of measurements that are averaged,
the slower the averaged sample rate, but the lower the noise error. Trade-offs between speed and
noise are normally required to tailor the instrumentation to your measurement application.
If you create test algorithms and you are using the averaging filters, make sure the algorithms clear
the filter memory stacks at appropriate times to avoid averaging an inappropriate set of
measurements.
Repeating average filter
When the repeating average filter is selected, a set of measurements are made, which are stored in a
measurement stack and averaged together to produce the averaged sample. Once the averaged
sample is produced, the stack is flushed and the next set of data is used to produce the next
averaged sample. This type of filter is the slowest, since the stack has to be completely filled before
an averaged sample can be produced.
Moving average filter
When the moving average filter is selected, the measurements are added to the stack continuously
on a first-in, first-out basis. As each measurement is made, the oldest measurement is removed from
the stack. A new averaged sample is produced using the new measurement and the data that is now
in the stack.
Note that when the moving average filter is first selected, the stack is empty. When the first
measurement is made, it is copied into all the stack locations to fill the stack. A true average is not
produced until the stack is filled with new measurements. The size of the stack is determined by the
filter count setting.
