Functional Overview
VX4792 User Manual
2-11
Data Length
You can specify the number of horizontal data points within a waveform using
the command (see page 3–37) before an equation compiles.
Data point values must be multiples of eight, ranging between 64 points and
256 K points.
Generating high-precision (high S/N ratio) waveforms requires an adequate
number of data points. For example, triangular waveforms require about 8000
points to minimize the jaggedness of the waveform. The waveform generator
uses a Digital-to-Analog Converter with a 12-bit vertical resolution (4096 points)
for the vertical amplitude. This resolution allows the instrument to produce
complex output waveforms having any waveshape. Figure 2–9 shows the
relationship between triangular wave resolution and the number of data points.
Figure 2-9: Triangular Wave Resolution and Number of Data Points
You will seldom require the level of precision obtained when using maximum
resolution. When maximum resolution is not needed, fewer waveform points
may be used. In equation and waveform editing, the default value for the number
of waveform points is 1000. The size of a fold-back component for a 1000-point
sine wave is –60 dB, an acceptable level for most applications.
If you make a waveform with less than 1000 points, be sure to use a filter
because you are using the maximum clock frequency. Note the following points:
H According to sampling theory, use of the ideal filter allows you to reproduce
the waveform with only two points of data for the highest frequency
component in the waveform. The filters in the waveform generator have
Bessel functions with relatively gentle shoulder characteristics to eliminate
overshoot and ringing. This is why more points are required.
H The amount of data required depends on the waveform shape, the desired
S/N ratio, the filter cutoff frequency, and other factors. Check the waveform
on an oscilloscope or spectrum analyzer to verify its characteristics.
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