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A record length must be selected
that has an adequate number of
points to reconstruct the desired
waveform. The waveform period
is 1 ms and there are 1000
carrier cycles in this period. A
record length of 20,000 points
would allocate 20 points per
cycle, which adequately over-
samples the ideal waveform.
Any sampling system must
sample at least twice as fast as
the analog bandwidth of the
underlying signal (i.e.,
1000 kHz). A sample rate of
20 MHz meets this criterion and
would require a record length of
20,000 points. In general, to
obtain reasonable results the
sample rate should be at least 3
times the analog bandwidth of
the underlying signal.
The AWG equation compiler
converts the waveform defini-
tion to a 1 ms series of 20,000
points (Figure 2). The AWG can
repetitively generate this series
to create the AM carrier in
Figure 3. The TDS 744A scope
captures the resulting waveform.
To aid in scope triggering, the
AWG was programmed to gener-
ate a marker signal once per
period on a separate output.
Figure 2. The AWG’s compiler converts the modu-
lation equation into a series of points that will
become the output record. The graphical display
provides an oscilloscope-like overview of the
record.
Figure 3. This is a TDS 744A oscilloscope display
of the modulated waveform; two complete AWG
records are shown in this two millisecond display.
The scope is triggered on one of the two marker
outputs from the AWG. The marker output was
programmed to generate a pulse once per record.