Agilent Technologies E1437A, User Manual

Page: 75 / 214

hpe1437_filter_setup
hpe1437_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
hpe1437_filter_decimate selects an extra factor of 2 decimation.
hpe1437_filter_decimate_get gets current state of extra decimation
hpe1437_filter_bw selects a signal filter bandwidth.
hpe1437_filter_bw_get gets the signal filter bandwidth
VXI plug&play Syntax
#include “hpe1437.h”
ViStatus hpe1437_filter_setup (ViSession id , ViInt16 sigBw , ViInt16 decimate );
ViStatus hpe1437_filter_decimate (ViSession id , ViInt16 decimate );
ViStatus hpe1437_filter_decimate_get (ViSession
id
, ViPInt16
decimatePtr
);
ViStatus hpe1437_filter_bw (ViSession id , ViInt16 sigBw );
ViStatus hpe1437_filter_bw_get (ViSession id , ViPInt16 sigBwPtr );
Parameters
id is the VXI instrument session pointer returned by the hpe1437_init function.
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 zoomfilter bandwidth is centered on the
frequency programmed with the
hpe1437_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 24. 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
k=.62 for 110 dB bandwidth
For even more accuracy use the hpe1437_filter_resp_get function.
sigBwPtr contains the current value of the sigBw parameter.
decimate
selects the data output sample rate. When this parameter is set to
HPE1437_OFF the output sample rate is: fs when sigBw =0 or fs /2^(sigBw-1) when
sigBw >0. When decimate is set to HPE1437_ON the output sample rate is reduced by
an additional factor of two by discarding alternate samples. You would normally want
to add the extra level of decimation in order to increase the displayed span.
E1437A User's Guide
VXI
plug&play Programming Reference
4-28
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