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Comments on a Design Procedure 321
8.5. Comments on a Design Procedure
A complete design procedure will be described with the aid of a flowchart.
The 13 major steps will be described, especially several topics that have not
been discussed so far. These are design limitations, optimization of shunt
inductance values, sensitivities, and filter tuning.
8.5.1. Design Flowchart. A step-by-step design procedure suitable for manual
computation or computer programming is shown in Figure 8.28. The
design step numbers correspond to the numbers of the main section headings
in Appendix G and to the last number of the subsection headings in Section
8.6. The following discussion emphasizes each step as previously described or
currently introduced.
The choice of a passband shape in step 1 is really a choice of loaded-Q
distribution. Element constraints are sometimes sufficiently severe to dictate
the use of an arbitrary set of loaded-Q values; the passband shape then is
nameless and can be determined only by analysis. The stopband estimates are
still viable, but step 3 has been preempted. Otherwise, one of the four shapes
discussed in Section 8.4 is selected, or a new prototype shape is developed to
provide a (normalized) loaded-Q distribution. Conventional shape specifications
are: (I) the number of resonators (poles); (2) the passband parameter
(such as decibel ripple, droop, or QdQu); (3) the fractional passband width
(Fp) and loss (L p )'
Step 2 in Figure 8.28 is to choose the configuration (e.g., Figure 8.2), the
midband frequency (e.g., Figure 8.3), and the allowable ranges of component
values (i.e., 1,,, L" [ and ~"C" C, where the underlines and overlines
indicate lower and upper bounds, respectively). Generally, the shunt inductor
Qu values are the resonator Qu values, because resonator capacitors usually
have relatively little loss and inverter dissipation has little effect.
A specific passband shape is obtained by a unique loaded-Q distribution
among the resonators in the absence of inverter frequency effects. The actual
level to which this distribution is scaled can be determined by knowledge of
the "QLNFp" product for the shape. These values are easily calcu!!lted and
tabulated, so that specification of Fp determines QLN' Thus, the N QL values
normalized to QLN (also tabulated versus shape) can be unnormalized. Step 3
in Figure 8.28 concerns this calcUlation. The stopband specifications may
result in greater QLN values than those resulting from the passband specification.
Step 3 records the decision that the pass band may be more important,
because selectivity increases and passband width decreases with increasing
loaded Q (increased stored energy). Loss effects in the passband must also be
considered in step 3. Dissipation tends to mask ripples, especially at the
passband edges. However, the minimum-loss shape is known in the presence
of uniform resonator dissipation.
Step 4 is based on the fact that stopband selectivity is completely specified