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Nouvelles techniques d'appariement dynamique dans un CNA multibit pour les convertisseurs sigma-delta

Abstract : ¢§ analog-to-digital converters can reach very high resolutions. The use of a multibit quantizer and of a multibit DAC reduces the oversampling ratio and the constraints imposed by active circuits, and improves the modulator loop stability. However, a multibit modulator is very sensitive to imperfections of its internal DAC located in feedback path. The static errors due to the non idealities of the DAC circuits can be corrected by means of dynamic element matching techniques (DEM). The aim of this PhD thesis is the theoretical study of several mismatch shaping techniques for a multibit feedback DAC used in delta-sigma modulators. After a presentation of the principle of ¢§ conversion and the main error sources in the multibit case, the existing DEM techniques are analyzed and compared. We underline advantages, disadvantages, and preferred application for each of them. The main part of this work consists in the development of four new DEM techniques. The first two derive from data-weighted averaging (DWA), one for first-order lowpass application, and the other for the case of second-order bandpass application. The last two proposals (called MDEM and STDEM) derive from the vector-based (SDEM) and tree-structured (TDEM) algorithms: they are more suitable for a high-order mismatch-shaping algorithm for both lowpass and bandpass applications. These four suggested methods are put in equation and their performances are confirmed by system-level simulations. A standard cell-level implementation of MDEM and STDEM techniques is performed in CMOS 0.35¹m technology. Simulations confirm the advantage of the developed techniques in terms of area and maximum frequency, compared with the conventional SDEM algorithms. In the last part, the DAC's dynamic errors such as clock jitter effects, glitch, non symmetrical transition times and clock-feedthrough (CFT), as well as quantizer metastability, are also analyzed. A new kind of DAC cell including a swing-reduced driver (SRD) is proposed. It has a partial return to zero structure (semi-RZ) which makes it possible to benefit at the same time from the advantages of RZ and non-RZ cells. Moreover, the DEM delay effect is compensated by a modification in the modulator architecture for high frequency bandpass applications.
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Submitted on : Tuesday, May 13, 2008 - 9:18:11 AM
Last modification on : Wednesday, November 29, 2017 - 3:39:27 PM
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  • HAL Id : tel-00278389, version 1



Esmaeil Najafi Aghdam. Nouvelles techniques d'appariement dynamique dans un CNA multibit pour les convertisseurs sigma-delta. Micro et nanotechnologies/Microélectronique. Université Paris Sud - Paris XI, 2006. Français. ⟨tel-00278389⟩



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