HDO4000 High Definition Oscilloscope
Calculating Measurements
Determining Top and Base Lines
Proper determination of the top and base reference lines is fundamental for ensuring correct parameter
calculations. The analysis begins by computing a histogram of the waveform data over the time interval
spanned by the left and right measurement gates. For example, the histogram of a waveform transitioning
in two states will contain two peaks (see figure). The analysis will attempt to identify the two clusters
that contain the largest data density. Then the most probable state (centroids) associated with these two
clusters will be computed to determine the top and base reference levels: the top line corresponds to the
top and the base line to the bottom centroid.
Determining Rise and Fall Times
Once top and base are estimated, calculation of the rise and fall times is easily done (see figure). The
appropriate threshold levels are automatically determined by the instrument, using the amplitude (ampl)
parameter.
Rising Edge Duration
Falling Edge Duration
Where
Mr
is the number of leading edges found,
Mf
the number of trailing edges found,
the time when
rising edge
i
crosses the x% level,
and the time when falling edge
i
crosses the x% level.
922498 Rev B
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