Circuits and Errors: Systematic Analysis and Practical Design Issues
As discussed in Chapter 1, ADCs based on modulation offer key advantages for their practical implementation in present-day CMOS processes compared with other data-conversion techniques. Unlike Nyquist-rate converters, which require high precision in their building blocks to achieve overall high accuracy, oversampling and quantization noise shaping allow to trade speed for accuracy. In this way, an operation that can be made relatively insensitive to imperfections on the analog circuit can be obtained at the cost of increased complexity and speed in the associated digital circuitry .
The principles of modulation were presented in the previous chapter and alternative M topologies (single-loop and cascades) and implementation techniques (DT and CT) were presented. However, the achievable performance of different alternatives was mainly addressed taking only quantization error into account. Besides this error—which is inherent to any analog-to-digital conversion technique—only the effect of DAC errors was considered to compare the performance of single-bit and multibit Ms at the architectural level.