Chapter 2
NI 5450 Overview
©
National Instruments Corporation
2-25
NI PXIe-5450 User Manual
FIR Filter Type: Raised Cosine
Alpha Values: 0.1 to 0.4
This lowpass filter is commonly used in communications applications. The
passband of the raised cosine filter stops at 0.5 × (1
−
α
) of the I/Q Rate.
The stopband of the raised cosine filter begins at 0.5 × (1 +
α
) of the I/Q
Rate. The transition-band of the raised cosine filter (in dB) follows the
following formula:
where
S
is 0.5 × (1
−
α
)
f
is Frequency (fraction of the I/Q Rate)
Use the Raised Cosine Filter Alpha property or the
NIFGEN_ATTR_OSP_FIR_FILTER_RAISED_COSINE_ALPHA
attribute to
set the
α
value.
The following diagram shows an ideal raised cosine filter response with an
α
of 0.5. The frequency axis is scaled as a fraction of the I/Q Rate.
–
–
–
–
–
–
–
–
–
–
–
–
0
–10
–20
–30
–40
–50
Amplit
u
de (dB)
–60
–70
–80
–90
0
0.2
0.4
0.6
0.8
1
Fre
qu
ency
1.6
1.8
2
1.2
1.4
–100
–
–
–
–
–
–
–
–
–
–
