Chapter 6 167
Custom Arb Waveform Generator
Working with Filters
7. Press Mirror Table.
In a windowed sinc function filter, the second half of the coefficients are identical to the first
half, but in reverse order. The signal generator provides a mirror table function that automatically
duplicates the existing coefficient values in the reverse order; coefficients 16 through 31 are
automatically generated and the first of these coefficients (number 16) highlights, as shown in the
following figure.
8. For this example, the desired OSR is 4, which is the default, so no action is necessary.
The Oversample Ratio (OSR) is the number of filter coefficients per symbol. Acceptable values
range from 1 through 32; the maximum combination of symbols and oversampling ratio allowed by
the FIR Values editor is 1024. Remember, however, that the instrument hardware is limited to 64
symbols for real–time waveform generation, and 512 symbols for arbitrary waveform generation.
The number of symbols equals the number of coefficients divided by the oversample ratio.
Coefficient Value Coefficient Value Coefficient Value
0 −0.000076 6 0.043940 12 0.123414
1 −0.001747 7 0.025852 13 0.442748
2 −0.005144 8 −0.035667 14 0.767329
3 −0.004424 9 −0.116753 15 0.972149
4 0.007745 10 −0.157348
5 0.029610 11 −0.088484
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