Analog Integrated Circuit Design, 2nd Edition

Key Point: Oversampling converters relax the requirements placed on the analog circuitry at the expense of more complicated digital circuitry.

Oversampling A/D and D/A converters are popular for high-resolution medium-to-low-speed applications such as high-quality digital audio and baseband signal processing in some wireless systems. A major reason for their popularity is that oversampling converters relax the requirements placed on the analog circuitry at the expense of more complicated digital circuitry. This tradeoff became desirable with the advent of deep submicron CMOS technologies as complicated high-speed digital circuitry became more easily realized in less area, but the realization of high-resolution analog circuitry was complicated by the low power-supply voltages and poor transistor output impedance caused by short-channel effects. With oversampling data converters, the analog components have reduced requirements on matching tolerances and amplifier gains. Oversampling converters also simplify the requirements placed on the analog anti-aliasing filters for A/D converters and smoothing filters for D/A converters. For example, usually only a first- or second-order anti-aliasing filter is required for A/D converters, which can often be realized very inexpensively. Furthermore, a sample-and-hold is usually not required at the input of an oversampling A/D converter.