Table of Contents
Advertisement
100 ps
Input Signal
Sample Points
Equivalent Time
Sampled Signal
Figure 28. Basic Sampling. Sampled points are connected by interpolation
to produce a continuous waveform.
Starting and Stopping the Acquisition System
One of the greatest advantages of digital oscilloscopes is their ability to
store waveforms for later viewing. To this end, there are usually one or
more buttons on the front panel that allow you to start and stop the
acquisition system so you can analyze waveforms at your leisure.
Additionally, you may want the oscilloscope to automatically stop
acquiring after one acquisition is complete or after one set of records
has been turned into an envelope or average waveform. This feature is
commonly called single sweep or single sequence and its controls are
usually found either with the other acquisition controls or with the
trigger controls.
Sampling
Sampling is the process of converting a portion of an input signal into
a number of discrete electrical values for the purpose of storage,
processing and/or display. The magnitude of each sampled point is
equal to the amplitude of the input signal at the instant in time in which
the signal is sampled.
1 Volt
1 Volt
100 ps
XYZs of Oscilloscopes
Sampling is like taking snapshots. Each snapshot corresponds to a
specific point in time on the waveform. These snapshots can then
be arranged in the appropriate order in time so as to reconstruct the
input signal.
In a digital oscilloscope, an array of sampled points is reconstructed on a
display with the measured amplitude on the vertical axis and time on the
horizontal axis, as illustrated in Figure 28.
The input waveform in Figure 28 appears as a series of dots on the
screen. If the dots are widely spaced and difficult to interpret as a
waveform, the dots can be connected using a process called interpolation.
Interpolation connects the dots with lines, or vectors. A number of
interpolation methods are available that can be used to produce an
accurate representation of a continuous input signal.
Sampling Controls
Some digital oscilloscopes provide you with a choice in sampling method –
either real-time sampling or equivalent-time sampling. The acquisition
controls available with these oscilloscopes will allow you to select a sample
method to acquire signals. Note that this choice makes no difference for
slow time base settings and only has an effect when the ADC cannot
sample fast enough to fill the record with waveform points in one pass.
Sampling Methods
Although there are a number of different implementations of sampling
technology, today's digital oscilloscopes utilize two basic sampling methods:
real-time sampling and equivalent-time sampling. Equivalent-time
sampling can be divided further, into two subcategories: random and
sequential. Each method has distinct advantages, depending on the
kind of measurements being made.
Primer
23
www.tektronix.com
Advertisement
Table of Contents
