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Some Techniques to Improve the Performance of Delta-Sigma Modulators

TitleSome Techniques to Improve the Performance of Delta-Sigma Modulators
Publication TypeConference Paper
Year of Publication2004
AuthorsCeballos, J. L., and G. C. Temes
Conference NameX. IBERCHIP Workshop
Date Published03/2004
Conference LocationCartagena de Indias, Columbia

In this paper some new and/or modified topologies for multi-bit DS A/D modulators will be shown. The main results are proven by means of extensive high-level simulations, modeling non-idealities in devices.

First, novel results are presented showing that requantization is feasible. The proposed system is stable for a 1-bit DAC only if the truncation error (T) is shaped with a first order loop. Comparing results with other structures, this one is especially well suited to be implemented with low-resolution analog components. For low oversampling ratios (OSR) the structure presents better performance than the Leslie-Singh’s [1] structure, because the difference between the analog and the digital transfer functions that the truncation error follows to the output is also shaped by a first order digital DS modulator.

Next, a structure that allows low distortion is presented. The architecture could be considered as an extension of the Chain Of Integrators with Distributed Feedback [3] topology, mixed with the low distortion topology of the Silva’s structure [4].
The use of spatial redundancy is also studied, which can improve the robustness under noisy conditions. Some related results are provided.

Also it is shown that the use of a non uniform quantizer which follows a linear step increase can improve the Dynamic Range (DR) with a little penalty in the Signal to Noise Ratio (SNR) of the system.

Finally the idea of Pseudo-Tangential Noise Transfer Function (PT-NTF) modulators is given. Useful for multi-bit modulators, this technique can provide a moderate increase in the overall SNR with only a little modification in the coefficients of the low pass filter (integrators) of the modulator.