In this chapter we have presented numerous alternative means for realizing high-order filters. These techniques are: 1. Direct synthesis. 2. Cascade synthesis. 3. GIC immittance simulation. 4. Multiple-loop feedback (and feedforward) synthesis. The technique that will serve a given application best, is the one that meets the frequency-domain and statistical requirements with minimum hardware and engineering time. For all but the most tolerant applications, the direct approach is impractical. To minimize Op Amps, designs based on the use of single-amplifier biquads (SABs) are encouraged. A simple design method requiring minimum engineering time is the cascade approach. In most applications we find that cascade designs, with a 0.2 % resistor tuning capability, provide sufficient precision. To meet more challenging requirements, the SAB MF topologies in Fig. 5-49 are recommended. When the sections are assigned identical Q's, the FLF (PRB) design will provide lower sensitivities than will a corresponding cascade design. In fact, all MF designs can provide lower sensitivities than the cascade within the passband. However, lower in-band sensitivities will be achieved with either an LF or MLF design. Since LF designs can be derived directly from a properly terminated LC ladder network, the very low LF sensitivities can often be obtained with modest engineering effort. FLF filter is not only easy to design, it is the only topology whose output noise can remain independent of the overall filter gain and the type of second-order section used [P27]. Finally, when the LF, MLF, and FLF designs do not quite satisfy requirements, an optimized MSF design should be tried.

Chapter Contents:

• 5.1 Introduction
• 5.2 Direct Synthesis Approach
• 5.3 Cascade Realizations
• 5.4 Active-Ladder Realizations
• 5.5 Multiple-Loop Feedback (and Feedforward) Methods
• 5.6 Follow-the-Leader-Feedback (FLF)-Type Filters
• 5.7 Leap-Frog (LF)-Type Filters
• 5.8 Minimum-Sensitivity-Feedback (MSF) Topology
• 5.9 Design Examples and Comparative Discussion of MF Designs
• 5.10 Minimum Op Amp MF Realizations
• 5.11 Summary
• References
• Problems

Inspec keywords: LC circuits; frequency-domain analysis; higher order statistics; ladder filters; operational amplifiers; biquadratic filters

Other keywords: GIC immittance simulation; SAB MF topology; frequency-domain analysis; FLF filter; operational amplifier; multiple-loop feedback synthesis; single-amplifier biquad filter; FLF-PRB design; in-band sensitivity; cascade synthesis; direct synthesis; high-order filter realization; high-order statistics; terminated LC ladder network

Subjects: Amplifiers; Other topics in statistics; Active filters and other active networks; Mathematical analysis