High-Resolution, Efficient Incremental Sigma-Delta Modulators
Sigma-Delta (ΣΔ) ADCs are suitable for various applications, due to its oversampling and noise-shaping behavior, thus high resolutions can be achieved independent on the matching accuracy of the analog components. For multiplexed applications, where an ADC is used to digitize the input coming from multi-channels, a sample-by-sample conversion is necessary. Regardless of the many advantages of Sigma-Delta ADCs, each output sample is dependent on the preceding one, therefore, a sample-by-sample conversion is not possible. As a result, Nyquist-rate ADCs (e.g SAR ADC) are dominant in the field of multiplexed applications.
On the other hand, Incremental Sigma-Delta (I-ΣΔ) ADCs have gained an increased interest in the past few years, as they inherit the basic properties of a freely-running ΣΔ modulators, however by resetting the internal states of the modulator and the following digital filter within the ADC (Fig. 1), a sample-by-sample conversion is obtained, and a true Nyquist-rate conversion is achieved. This allows I-ΣΔ ADCs to compete with other Nyquist-rate ADCs (e.g. SAR ADC) with the potential of achieving high resolutions, due its insensitivity to element mismatches.
The field of I-ΣΔ modulators is considered a trending young field of research, with many unexplained phenomena and unique properties different from the freely-running ΣΔ ADC, giving it an extra degree of freedom. Thus, more solutions and ideas to overcome the design challenges and achieve high-resolution power efficient designs are much desired.