9.8: SUMMARY

9.8 SUMMARY

The application of switched capacitor circuits compatible with CMOS technology has been presented in this chapter. The key advantage of switched capacitor circuits is that the precision of signal processing becomes proportional to the capacitor ratios, which is probably the most accurate aspect of CMOS technology. We have seen that, in most cases, it is necessary for the clock frequency to be much greater than the signal bandwidth. If this is the case, then the equivalence between the sampled-data domain and time domain is straightforward.

All the switched capacitor circuits discussed in this chapter are two phase. While this simplifies the considerations, there are many applications that divide the clock period into more than two segments. It is necessary that the clocks be nonoverlapping regardless of the number of phases. A disadvantage of switched capacitor circuits is the clock feedthrough that occurs via the overlap capacitance of the switches. While the feedthrough can be minimized, it represents the ultimate accuracy of the switched capacitor circuit.

Applications of switched capacitor circuits including amplifiers, integrators, and filters have been considered. Switched capacitor filters represent an application that has reached maturity and is widely used. Unfortunately, the signal bandwidth must be less than the clock frequency in most switched capacitor filters, which prevents the filter from being able to accomplish signal filtering near the bandwidths of the op amps. Switched capacitor circuits are a viable way of accomplishing precision analog signal processing and will be used extensively in the next chapter...