Programming instructions
Downloading and Using Files
FIR Filter Coefficient Downloads
Chapter 4 179
FIR Filter Coefficient Downloads
The signal generator accepts finite impulse response (FIR) filter coefficient downloads. After
downloading the coefficients, these user-defined FIR filter coefficient values can be selected as
the filtering mechanism for the active digital communications standard.
Data Requirements
There are two requirements for user-defined FIR filter coefficient files:
1. Data must be in ASCII format.
The signal generator processes FIR filter coefficients as floating point numbers.
2. Data must be in List format.
FIR filter coefficient data is processed as a list by the signal generator’s firmware. See
“Sample Command Line” on page 185.
Data Limitations
Filter lengths of up to 1024 taps (coefficients) are allowed. The oversample ratio (OSR) is the
number of filter taps per symbol. Oversample ratios from 1 through 32 are possible.
The maximum combination of OSR and symbols allowed is 32 symbols with an OSR of 32.
The Real Time IQ Baseband FIR filter files are limited to 1024 taps, 64 symbols and a
16-times oversample ratio. FIR filter files with more than 64 symbols cannot be used.
The ARB Waveform Generator FIR filter files are limited to 512 taps and 512 symbols.
The sampling period (
∆
t) is equal to the inverse of the sampling rate (FS). The sampling rate
is equal to the symbol rate multiplied by the oversample ratio. For example, the GSM symbol
rate is 270.83 ksps. With an oversample ratio of 4, the sampling rate is 1083.32 kHz and
∆
t
(inverse of FS) is 923.088 nsec.
Data Volatility
The signal generator provides two data storage areas: volatile waveform memory (WFM1) and
non-volatile memory (NVWFM). FIR filter coefficients stored in volatile waveform memory
cannot be recovered if overwritten or if the power is cycled. Coefficients stored in non-volatile
memory, however, remain until you delete the file. The Option 005 signal generator’s hard
disk provides 6 Gsamples of non-volatile storage. Signal generators without Option 005
provide 3 Msamples of non-volatile storage.