Analog MOS Integrated Circuits for Signal Processing

Chapter Eight

SYSTEM CONSIDERATIONS AND APPLICATIONS

Switched-capacitor circuits are usually fabricated as parts of a larger signal processing system, although some programmable filters have also been made commercially available as stand-alone units. As system components, SC circuits must be compatible with the other parts of the system, and must also satisfy its overall specifications.

In this chapter, we first discuss the specific design considerations associated with the sampled-analog character of SC circuits, discussed earlier in Chapter 2. Then, a number of fully integrated signal processing systems incorporating SC components are described. In selecting these examples, the authors gave preference to devices which they (especially R.G.) were instrumental in designing. This was motivated both by familiarity and emotional involvement. We hope that the reader excuses this bias.

8.1. PREFILTERING REQUIREMENTS FOR SWITCHED-CAPACITOR FILTERS

As discussed in Section 2.5, both the sampling or sample-and-hold (S/H) operations result in the replication of the spectrum of the input signal, and (unless Nyquist's criterion is satisfied) introduce aliasing distortion. Therefore, SC circuits which perform a S/H function are vulnerable to aliasing. To prevent this, in general, a low-pass continuous-time analog antialiasing filter (AAF) is required before a continuous-time signal can be processed ...