High-Performance Data Converters

Novel techniques for multi-bit oversampled data conversion are described. State-of-the-art oversampled data converters are analyzed, leading to the conclusion that their performance is limited mainly by low-resolution signal representation. To increase the resolution, high-performance, high-resolution internal D/A converters are required. Unit-element mismatch-shaping D/A converters are analyzed, and the concept of mismatch-shaping is generalized to include scaled-element D/A converters. Several types of scaled-element mismatch-shaping D/A converters are proposed. Simulations show that, when implemented in a standard CMOS technology, they can be designed to yield 100 dB performance at 10 times oversampling. The proposed scaled-element mismatch-shaping D/A converters are well suited for use as the feedback stage in oversampled delta-sigma quantizers. It is, however, not easy to make full use of their potential, because that requires a high-resolution loop quantizer which introduces only a small delay. Generally, it is not acceptable to design the loop quantizer as a high-resolution flash quantizer because they require a large chip area and high power consumption. Pipeline techniques are proposed to circumvent this problem. This way, the delta-sigma quantizer’s feedback signal is obtained by a multiple-stage quantization, where the loop quantizer (low-resolution and minimum-delay) implements only the last-stage quantization. Hence, high-speed, high-resolution delta-sigma quantization is feasible without using complex circuitry. An improved version of the MASH topology is also proposed. A delta-sigma quantizer is used to quantize the input signal into an oversampled digital representation of low-to-moderate resolution. The deltai