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Using Area-based Templates for Pass/Fail Limit Waveform Testing
Area-based Templates
Area-based templates represent an improvement over the
standard “+/-“ band type of templates by offering more
flexibility in template creation. Users are able to create
more complex tolerance bands to address a wider variety
of applications. Figure 3 shows an example in which an
area-based template is being used to test rise-time.
The TBS1000B Series of oscilloscopes supports the
creation of standard line-based templates based on a single
waveform as well as enhanced templates using two reference
waveforms. In Dual Ref mode, a user can define a limit testing
tolerance band as the area between the two reference
waveforms with specific horizontal and vertical tolerances —
in other words, an area-based template.
Solving Problems Quickly
Let’s say you are working with a Keithley Series 2280S-32-6
Programmable DC Power Supply. This instrument has
a programmable voltage slew rate when in constant voltage
mode.
Imagine that your goal is to build an automatic test to ensure
that the product’s output fall times are within an acceptable
range for a number of slew rate settings.
In this case, the specification indicates that the discharge time
should fall within 10 milliseconds to 50 milliseconds. During
the discharge time the voltage should smoothly decrease from
90% of V
out
to 10% of V
out
. (V
out
= 5V).
An automatic limit test would be a great solution, but the
standard single reference template would not be adequate in
this case. As the capacitor discharge time can be anywhere
within 10 milliseconds to 50 milliseconds, the tolerances
will change the farther the waveform gets from the trigger.
A limit test is needed that can accommodate this more
complex condition.
Figure 3. Area-based template to evaluate the rise time of a signal.