Displaying Waveforms
3- 134
CSA7000B Series & TDS7000B Series Instruments User Manual
Normal and Persistence Displays. Use the display persistence to control how
waveform data ages:
H Off style displays waveforms without persistence: each new waveform
record replaces the previously acquired record for a channel. You can choose
to display normal waveforms as vectors, which displays lines between the
record points or dots (vectors off) which displays the record points only. You
can also choose an interpolation mode. See Interpolation on page 3--134.
H Variable Persistence style accumulates the waveform-record points on screen
and displays them only for a specific time interval. Previous waveform data
continuously fades from the display as new waveform records acquire.
H Infinite Persistence style accumulates the data record points until you change
some control (such as scale factor) causing the display to be erased.
Waveform data builds up as new data records acquire.
Persistence style is only available for live waveforms (waveforms with data that
is being updated); reference waveforms are static and do not use persistence.
Math waveforms use persistence if their sources are live waveforms.
Interpolation. When, due to preview, zoom, or Real Time mode with limited
samples, the available sample density falls to less than 1 sample per display
column, the instrument calculates intermediate points by either the linear or sine
algorithms, and uses them to produce points. There are two options for interpola-
tion:
H Sin(x)/x interpolation computes record points using a curve-fit between the
actual values acquired. The curve-fit assumes all the interpolated points fall
along that curve. Sin(x)x interpolation is particularly useful when acquiring
more rounded waveforms such as sine waves. It is also appropriate for
general use, although it may introduce some overshoot or undershoot in
signals with fast rise times.
H Linear interpolation computes record points between actual acquired samples
by using a straight-line-fit. The straight-line-fit assumes all the interpolated
points fall in their appropriate point in time on that straight line. Linear
interpolation is useful for many waveforms such as pulse trains.
Interpolation is used whenever the displayed sample density falls below 1 sample
per column. If the acquired record length is 500 points, zoom of 2x requires
interpolation. If instead, the record length of the acquisition is 100K, horizontal
zoom of 200x produces 1 sample per column (100,000/500 = 200); therefore,
you will see interpolated samples starting at the next scale setting.
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