Abstract — Oversampling techniques based on sigma-delta (ΣΔ) modulation offer numerous advantages for the realization of high-resolution analog-to-digital (A/D) converters in a low-voltage environment. This paper examines the design and implementation of a CMOS ΣΔ modulator for digital-audio A/D conversion that operates from a single 1.8-V power supply. A cascaded modulator that maintains a large full-scale input range while avoiding signal clipping at internal nodes is introduced. The experimental modulator has been designed with fully-differential switched-capacitor integrators employing different input and output common-mode levels and boosted clock drivers in order to facilitate low voltage operation. Precise control of common-mode levels, high power supply noise rejection, and low power dissipation are obtained through the use of two-stage, class A/AB operational amplifiers. At a sampling rate of 4 MHz and an oversampling ratio of 80, an implementation of the modulator in a 0.8-μm CMOS technology with metal-to-polycide capacitors and NMOS and PMOS threshold voltages of +0.65-V and –0.75-V, respectively, achieves a dynamic range of 99 dB at a Nyquist conversion rate of 50 kHz. The modulator can operate from supply voltages ranging from 1.5 V to 2.5 V, occupies an active area of 1.5 mm 2, and dissipates 2.5 mW from a 1.8-V supply.

Design automation for analog/mixed-signal (A/MS) circuits and systems is still lagging behind compared to what has been reached in the digital area. As System-on-Chip (SoC) designs include analog components in most cases, these analog parts become even more a bottleneck in the overall design process. The paper is dedicated to latest R&D activities within the MEDEA+ project ANASTASIA+. Main focus will be the development of seamless top-down design methods for integrated analog and mixed-signal systems and to achieve a high level of automation and reuse in the A/MS design process. These efforts are motivated by the urgent need to close the current gap in the industrial design flow between system specification and design on the one hand and block-level circuit design on the other hand. The paper will focus on three subtopics starting with the topdown design flow with applications from circuit sizing, design centering, and automated behavioral modeling. The next part focuses on modeling and simulation of specific functionalities in sigma-delta design while the last section is dedicated to a mixed-signal System-on-Chip design environment. 1.

The paper presents a quantization-theoretic framework for studying incremental Σ∆ quantization systems. The framework makes it possible to efficiently compute the quantization intervals and hence the transfer function of the quantizer, and to determine the mean square error (MSE) and maximum error for the optimal and conventional linear filters for first and second order incremental Σ∆ modulators. The results show that the optimal filter can significantly outperform conventional linear filters in terms of both MSE and maximum error. The performance of conventional Σ∆ quantizers is then compared to that of incremental Σ∆ with optimal filtering for bandlimited signals. It is shown that incremental Σ∆ can outperform the conventional approach in terms of signal to noise+distortion ratio (SNDR) and the characteristics of the power spectral density (PSD). The framework is also used to provide a simpler and more intuitive derivation of the Zoomer algorithm.