DESIGN AND ANALYSIS OF ANALOG FILTERS A Signal ...

316 DESIGN AND ANALYSIS OF ANALOG FILTERS:
Values for Filter Selectivity may be obtained from (9.45). Values for and
for use in (9.45) may be obtained from an equation derived similarly as (9.42):
From (9.49), and these values are also
observable in the data plotted in Figure 9.16. Note that It
follows from (9.45) that and 0.0620 for and respectively.
These values may also be obtained from the data plotted in Figure 9.16.
The value of the Shaping Factor may be obtained from (9.46). Note that
, where a = 3dB and b =80dB. Therefore, from (9.46),
where and
These values are also obtainable from the data plotted in Figure 9.15.
For a 5th-order elliptic lowpass filter, the frequencies where the magnitude
frequency is zero are obtained from (5.7) to be and The
frequencies where the magnitude response equals in the stopband are obtained
from (5.8) to be and From the basic mapping for a lowpassto-bandstop
frequency transformation,
where is the radian frequency variable for the lowpass prototype, and is the
radian frequency variable for the bandstop filter. From (9.50) it follows that
Chapter 9 Frequency Transformations