Agilent Technologies E8257D, Руководство пользователя

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166 Chapter 6
Custom Arb Waveform Generator
Working with Filters
To Create a User–Defined FIR Filter with the FIR Values Editor
In this procedure, you use the
FIR Values
editor to create and store an 8–symbol, windowed, sinc
function filter with an oversample ratio of 4. The Oversample Ratio (OSR) is the number of filter
coefficients per symbol.
You can define from 1 to 32 FIR coefficients, where the maximum combination of symbols and
oversample ratio is 1024 coefficients.
The FIR Values editor allows a maximum filter length of 1024 coefficients, but the PSG hardware is
limited to 512 symbols for arbitrary waveform generation, and 64 symbols for real–time waveform
generation. The number of symbols equals the number of coefficients divided by the oversample ratio.
If you enter more than the maximum number of symbols, the PSG cannot use the filter; it decimates
the filter (throws away coefficients) until the required condition is met and then uses the filter, but
fine resolution may be lost from the impulse response.
1. Press
Preset
.
2. Press
Mode
>
Custom
>
Arb Waveform Generator
>
Digital Mod Define
>
Filter
or
Mode > Custom > Real Time I/Q Baseband > Filter
3. Press
Define User FIR
>
More (1 of 2)
.
4. Press
Delete All Rows
>
Confirm Delete Of All Rows
>
More (2 of 2)
.
This brings up the FIR Values editor and clears the table of existing values.
5. Press
Edit Item
. The
Value
field for coefficient 0 should be highlighted.
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.