Agilent Technologies VXI E1439 - Manual (Page 131)

121
Agilent E1439 Programmer's Reference
Functions listed alphabetically
k=.62 for 110 dB bandwidth
AGE1439_SIG_BW_MAX sets sigBw to the maximum value and the filter bandwidth to the
minimum.
AGE1439_SIG_BW_MIN sets sigBw to the minimum value and filter bandwidth to the
maximum.
sigBwPtr points to the current value of the sigBw parameter.
Caution
Selecting AGE1439_DECIMATE_ON when sigBw=0 results in aliasing (garbage data) due
to upper limit of the sampling frequency and, therefore, causes the SETUP_ERROR bit to
be set.
Selecting AGE1439_DECIMATE_SHIFT for non-zoomed data is not a useful configuration.
Comments
To ensure full alias-free operation the analog anti-alias filter (set by the age1439_input_alias_
filter function) should be ON unless the application inherently bandlimits the input signal to less
than fs/2. The analog anti-alias filter has a fixed bandwidth and thus is fully effective only when fs
≥ 100 MHz. If a slower external ADC clock is used, an additional analog filter of the appropriate
bandwidth may be required for full alias protection.
The decimation process used to reduce the output sample rate is driven from a "decimation
counter" which keeps track of which samples to save and which ones to discard for each of the
octave bandwidth reduction filter stages. In multi-module systems where synchronous sampling is
required, the decimation counters in all the modules must be synchronous with each other. This
condition can be forced by using the age1439_filter_sync function.
The following table lists parameter combinations (see also “age1439_data_setup” on page 90 )
which result in invalid measurement conditions:
All other combinations are valid.
Example
Here are some bandwidth and sample rate results using the "k" calculation for bandwidth:
fs = 100 MHz default internal ADC clock (all data in MHz)
Invalid parameter combinations
resolution
(bits)
dataType decimate sigBw
12 or 24 REAL or COMPLEX OFF or SHIFT 1
12 or 24 REAL or COMPLEX ON or SHIFT 0
12 or 24 COMPLEX any 0
24 REAL or COMPLEX OFF 2
24 REAL or COMPLEX any 0 or 1
12 or 24 COMPLEX SHIFT any