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332 Direct-Coupled Filters
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Figure 8.31.
Typical undercoupled deviation from linear phase.
Using a least-squares fitted line as a phase reference, a frequency analysis
provided the typical deviation from linear phase shown in Figure 8.31. The
gentle rate of change of the undercoupled response (Figure 8.26) is directly
related to good phase linearity. Its moderate selectivity has been supplemented
in the upper stop band, at the expense of the lower stopband in this case,
without seriously disturbing the passband.
The maximum sensitivity of input impedance with respect to capacitance
occurs at node 3 with C m ; according to (G.85), it is ±j7.216.
8.6.13. Design Adjustment. The exact analysis in the preceding section also
confirmed the phase angles between nodes at the midband frequency (f o = 100
MHz). As in (G.87) and Figure 8.2, angle 0Gl was 30.6 degrees, and the other
node voltage angles differed by the expected 90 degrees, according to the
prototype network (Figure 8.1).
Problems
8.1. Use ABCD parameters to prove that Zin=ZVZL for an ideal inverter.
8.2. Consider the following network:
lin
I
I
z
+ +
-z -z Iz,
\lin
V,
I I I
I
II,
I
I