Location: page 254, line -10 to page 255, line 9
In the description of the gain and phase curves in Example 8.8, there are multiple errors:
- The breakpoint frequencies should use
instead of 
in the text and in Figure 8.14;
- The frequencies where the breakpoints occur are not the locations of the poles and zeros. It is the effects of the poles and zeros that is relevant.
The correct text for the last two paragraphs of the exercise is given below:
We begin with the gain curve. At low frequency, the magnitude is
given by
When we reach 
, the effect of the
pole begins and the gain decreases with slope 
. At
, the zero comes into play
and we increase the slope by 1, leaving the asymptote with net slope 0.
This slope is used until the effect of the second-order pole is seen at
, at which point the asymptote changes to
slope 
. We see that the gain curve is fairly accurate except
in the region of the peak due to the second-order
pole (since for this case 
is reasonably small).
The phase curve is more complicated since the effect of the phase stretches
out much further. The effect of the pole begins at 
, at which point we change from phase 0 to a slope of
/decade. The zero begins to affect the
phase at 
, producing a flat section in the phase.
At 
the phase contributions from the pole end, and
we are left with a slope of 
/decade (from the zero). At
the location of the second-order pole, 
, we
get a jump in phase of 
. Finally, at
the phase contributions of the zero end, and we
are left with a phase of 
degrees. We see that the
straight-line approximation for the phase is not as accurate as it was for
the gain curve, but it does capture the basic features of the phase changes
as a function of frequency.
The correct version of Figure 8.14 is
(Contributed by L. Xiong, 29 Dec 08)
