Age1439_filter_setup, Filter_bw – Agilent Technologies VXI E1439 User Manual
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Agilent E1439 Programmer's Reference
Functions listed alphabetically
age1439_filter_setup
Sets the digital filter bandwidth and decimation filter parameters. This description also includes
information on the following functions which set or query the decimation filter parameters
individually:
age1439_filter_decimate selects an extra factor of 2 decimation.
age1439_filter_decimate_get gets current state of extra decimation
age1439_filter_bw selects a signal filter bandwidth.
age1439_filter_bw_get gets the signal filter bandwidth
VXIplug&play Syntax
#include "age1439".h
ViStatus age1439_filter_setup(ViSession id, ViInt16 sigBw, ViInt16 decimate);
ViStatus age1439_filter_decimate(ViSession id, ViInt16 decimate);
ViStatus age1439_filter_decimate_get(ViSession id, ViPInt16 decimatePtr);
ViStatus age1439_filter_bw(ViSession id, ViInt16 sigBw);
ViStatus age1439_filter_bw_get(ViSession id, ViPInt16 sigBwPtr);
Parameters
id
is the VXI instrument session pointer returned by the age1439_init function.
decimate
selects the data output sample rate. When this parameter is set to
the output sample rate is:
fs when sigBw=0, or
fs/2^
(sigBw-1)
when sigBw>0
When decimate is set to
the output sample rate is reduced by an
additional factor of two by discarding alternate samples.
is like AGE1439_DECIMATE_ON but additional processing is
performed that shifts the center frequency of zoomed data up by fs/4 and transforms the complex
data stream into a real data stream without losing phase information. For consistent spectrum
measurements the data scale value is doubled when using shift decimate.
decimatePtr
points to the current value of the decimate parameter.
sigBw
selects an alias protected signal filter bandwidth that is roughly ±fs/(2.56 × 2^
(sigBw)
) where fs is
the ADC sample frequency. In zoom applications, where the center frequency is generally not
zero, the zoom filter bandwidth is centered on the frequency programmed with the age1439_
frequency_setup function. For baseband measurements the filter may equivalently be considered
as a low pass filter of approximately bandwidth fs/(2.56 × 2^
(sigBw))
since the negative
frequencies are generally of no interest. The valid range of sigBw is 0 through 18. When sigBw =
0, no digital filtering is applied to the signal and the module relies on the analog anti-alias filter to
limit the signal bandwidth to fs/2.56.
To more accurately calculate the bandwidth use the calculation ±fs × k/2^
(sigBw)
where:
k=.36 for .25 dB bandwidth
k=.44 for 3 dB bandwidth
k=.5 for 15 dB bandwidth