High-Speed Oversampling Analog-to-Digital Converters

Abstract

This paper is mainly tutorial in nature and discusses architectures for oversampling converters with a particular emphasis on those which are well suited for high frequency input signal bandwidths. The first part of the paper looks at various architectures for discrete-time modulators and looks at their performance when attempting high speed operation. The second part of this paper presents some recent advancements in time-interleaved oversampling converters. The next section describes the design and challenges in continuous-time modulators. Finally, conclusions are made and a brief summary of the recent state of the art of high-speed converters is presented.

Design of a delayless feedback path free 2nd-order two-path time-interleaved discrete-time delta-sigma modulator- a new approach

“…The terms in ‫ݖ‬ ଶ in (21) show the effect of the up-samplers in the modulator. The term in (1 + ‫ݖ‬ ିଵ ) from the ‫)ݖ(ܨܶܵ‬ of the DTTI ΔΣ modulator shows the effect of removing the input demultiplexer of the DTTI ΔΣ modulator causing some notches in the STF as explained earlier on in the paper and as described in [5][6] [10]. Figure 5 shows the NTFs of the DT and the DTTI ΔΣ modulator.…”

“…A fast input demultiplexer which is a limiting factor for the performance of the DTTI ΔΣ modulators is necessary. However this input demultiplexer can be removed and the input signal simply shared between the two channels [5][6] [10]. The Signal Transfer Function (STF) of the DTTI ΔΣ modulator exhibits some notches in its response at the following frequencies ‫ܨ5.0‬ , ‫ܨ5.1‬ , ‫ܨ5.2‬ , ‫ܨ5.3‬ , … where ‫ܨ‬ is the clock frequency of the DTTI ΔΣ modulator resulting from the removal of the input demultiplexer.…”

“…The Signal Transfer Function (STF) of the DTTI ΔΣ modulator exhibits some notches in its response at the following frequencies ‫ܨ5.0‬ , ‫ܨ5.1‬ , ‫ܨ5.2‬ , ‫ܨ5.3‬ , … where ‫ܨ‬ is the clock frequency of the DTTI ΔΣ modulator resulting from the removal of the input demultiplexer. This modification and has no effect on the modulator's Noise Transfer Function (NTF) [5][6] [10].…”

Combining Multipath and Single-Path Time-Interleaved Delta-Sigma Modulators

“…This is different from traditional time-interleaved structures where each branch processes alternating samples [1]. The modified sampling has no effect on the NTFs of the modulator, however, the signal transfer function (STF) is changed [6]. The modified STF has a negligible effect on the achievable SNR.…”

“…The modified STF has a negligible effect on the achievable SNR. It introduces a notch at half the sampling frequency and an image of the signal [6]. However, due to oversampling, these modifications are not critical.…”