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130 Chapter 6
Custom Arb Waveform Generator
Working with Filters
6. Use the numeric keypad to type the first value (
−
0.000076) from the following table and press
Enter
. As
you press the numeric keys, the numbers are displayed in the active entry area. (If you make a mistake,
you can correct it using the backspace key.) Continue entering the coefficient values from the table until
all 16 values have been entered.
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
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