Tektronix, Inc. P6240, User Manual

Page: 71 / 321

Acquisition
2–20
TLS 216 User Manual
Sampling is the process of converting the analog input signal to digital data for
display and processing. (See Figure 2-5.)
Sampling Rate
Record Points
Figure 2-5: Real-Time Sampling
Two factors that affect real-time sampling are interleaving and interpolation.
Turning the Horizontal SCALE knob clockwise causes the scope to assign
shorter time periods to the waveform record. The smaller the time period gets,
the faster the logic scope needs to acquire record points to fill up the record.
If you turn the Horizontal SCALE knob to a point that the time base is faster
than 25 ns, the logic scope will not acquire enough samples for a complete
waveform record. When that happens, the logic scope uses a process called
interpolation to create the intervening points in the waveform record. There are
two options for interpolation: linear or sin(x)/x.
Linear interpolation computes record points between the samples acquired by
using a straight line fit. It 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.
Sin(x)/x interpolation computes record points using a curve fit between the actual
values acquired. It assumes all the interpolated points fall along that curve. That
is particularly useful when acquiring more rounded waveforms such as sine
waves. Actually, it is appropriate for general use, although it may introduce some
overshoot or undershoot in signals with fast rise times.
NOTE
. When using either type of interpolation, you may wish to set the display
style so that the real samples are displayed intensified relative to the interpolated
samples. The instructions under To Choose a Display Style on page 3–36
explain how to turn on intensified samples.
Sampling
Interpolation