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EX1629 Command Set
161
vtex1629_get_IIR_filter_configuration
F
UNCTION
P
ROTOTYPE
ViStatus vtex1629_get_IIR_filter_configuration (ViSession
vi
, ViInt32
channel
, ViPInt32
filterType
, ViPReal64
cutoffFreq
, ViPInt32
transform
, ViPInt32
filterOrder
, ViPReal64
groupDelay
);
F
UNCTION
P
ARAMETERS
vi
= contains a session handle to the instrument. This handle is obtained by the function and remains valid until the
session is closed.
channel
= an integer input value that specifies the channel for which the IIR filter configuration will be returned.
Valid input values: 0 to 47.
filterType
= an integer return value indicating the type of filter that is currently configured to be used for the given
channel. See
Description
below for more information. Valid return values: 0, 1, or 2.
cutoffFreq
= a real return value indicating the current cutoff frequency, in hertz (Hz), currently configured in filters
on the given channel. This parameter is only relevant for Bessel and Butterworth filter types. Valid return values:
0.001 to 4005.
transform
= an integer return value indicating the type of filter transform currently configured for the given
channel. This parameter is only relevant for Bessel and Butterworth filter types. Valid return values: 0 or 1.
filterOrder
= an integer return value indicating the order of the filter on a given channel. This parameter is only
relevant for Bessel and Butterworth filter types. Valid return values: 1 to 10.
groupDelay
= a real return value indicating the group delay, in number of samples, of the currently configured filter
for the given channel.
D
ATA
I
TEM
R
ESET
V
ALUE
Not applicable to this function.
D
ESCRIPTION
This function queries and returns the IIR filter configuration parameters for a given channel. The
filterType
parameter has three allowed values:
Decimal
Value
Hex
Value
#define Symbol
filterType Description
0
0x00
VTEX1629_IIR_FILT_NONE
None
1
0x01
VTEX1629_IIR_FILT_BUTTERWORTH
Butterworth
2
0x02
VTEX1629_IIR_FILT_BESSEL
Bessel
A value of “None” disables the IIR filters. Note, however, that the FIR filter is always enabled and is not user-
configurable.
The
cutoffFreq
parameter defines the cutoff (-3 dB) frequency for the low-pass filter indicated above. The EX1629
will locate this parameter in the range [
f
s
/1000,
f
c
max] (see Table B-1), where
f
s
is the current sampling frequency.
Note that this value can change if the sampling frequency is altered. The actual value can be queried with the
vtex1629_get_IIR_filter_configuration command.
The
transform
parameter provides for two modes of transformation:
Decimal
Value
Hex
Value
#define Symbol
transform Description
0
0x00
VTEX1629_TRANSFORM_BILINEAR
Bilinear
1
0x01
VTEX1629_TRANSFORM_MATCHEDZ
Matched-Z
The
filterOrder
parameter defines the desired order of the filter. When the
filterType
is set to Butterworth, there is
an additional option of 0. This corresponds to an automatic option, whereby the EX1629 will assign an order based
on an analog prototype Butterworth design given the sampling frequency, cutoff frequency, and a -200 dB
attenuation at the Nyquist frequency. The actual order can be determined using the command.
