Page 175 - DSP Integrated Circuits
P. 175
160 Chapter 4 Digital Filters
The adaptor coefficients in the four
allpass sections are
The poles are
The zeros are
The general form of the transfer
function is
where HQ(Z) is a first-order allpass ni- Figure 4.49 Seventh-order lowpass lattice
ter while the other sections are second- WDF
order allpass filters.
An important observation that simplifies the design is that the poles along the
imaginary axis alternate between the upper and lower branches of the lattice fil-
ter. Thus, the poles z p\ and 2^4,5 are realized by the upper branch while the poles
Z an z are
p2,3 d p&,l realized by the lower branch. Further, all zeros lie on the unit
circle.
The attenuation is shown in Figures. 4.50 and 4.51. The passband and stop-
band edges are
