Teledyne LeCroy DFP2 - Digital Filter Package 2 - Manual (Page 9)

DFP2 Option
923134 Rev A ISSUED: June 2013 7
Communications Channel Filters
Raised Cosine (a low-pass filter) These filters belong to the low-pass filter category (with
a variety of shapes). Raised cosine is one of a class of
filters used to minimize intersymbol interference: the
time domain impulse response crosses zero at all bit
time intervals except the one with the impulse.
Applying raised root cosine twice (or at the sending
and receiving end of a signal, for example) results in a
raised cosine filter effect. Sample applications include
wireless cellular communications such as WCDMA,
datacom, telecommunications, disk drive and optical
drive analysis.
Band 1: Pass Band — DC to corner frequency minus
half width; signal passes unattenuated.
Band 2: Transition Region — corner minus half width to
corner plus half width; attenuation increases with
frequency with a rolloff shape of 0.5cos(a) + 0.5, where
a ranges from 0 to p over the transition region. This
region is determined by b, which is specified as a
percentage of the corner frequency.
Band 3: Stop Band — above corner frequency plus half
width; highly attenuated.
The impulse function for the raised cosine filter is: