Derk Reefman

Description of limit cycles in sigma-delta modulators

A mathematical framework, based on state-space modeling, for the description of limit cycles (LCs) of 1-bit sigma-delta modulators (SDMs) is presented. It is proved that periodicity in bit output pattern of the SDM implies a periodic orbit in state-space variables. While the state-space description is generally applicable for periodic inputs, the focus is on dc inputs, since this represents the most relevant practical condition. An outcome of the analysis is that, in general, for an Nth-order SDM, at least N-1 initial conditions need to be fixed in order to have LC behavior. Expressions for the minimum disturbance of the input or initial conditions that is needed to break up a LC are also presented. Special focus is given to the case where the disturbance takes the form of dithering the quantizer, and it is shown that this form of dither is a suboptimal approach to remove LCs. The stability of LCs is determined, and it is demonstrated that a resonator section, as often employed to increase the dynamic range of an SDM, has an adverse effect on LC behavior in that it stabilizes LCs. Furthermore, the experimental observation that high order SDMs are less susceptible to LCs is underpinned. Finally, some examples are provided which illustrate the theoretical results.

Super-audio CD: an introduction

Super-audio compact disc (SACD), conceived and developed by Philips and Sony, is viewed as the successor of the standard CD. In March 1999 the standard was set, and Scarlet Book version 1.0 was released. Since then, the format changed from an audiophile release format to a mass-consumer format. Not only does SACD provide an enhanced listening performance to the end-user, it also provides strong copy protection for the music industry. These aspects, in combination with a basic introduction in signal processing for super audio, are discussed The article is concluded with an overview of some of the latest developments in high-quality DSD generation.

Lossless compression of one-bit audio

The paper introduces the coding technique that is used by the Super Audio CD system for lossless compression of 64 times oversampled one-bit audio data. The technique has been coined DST (direct stream transfer). The individual steps in the encoding and decoding process are detailed. The performance of the lossless compression algorithm, as a function of various music genres, is discussed. It is shown that 74 minutes of both stereo and multi-channel music, which translates to 12.5 GB of raw data, fit on the 4.7 GB Super Audio disc after compression. An extension to the algorithm for future professional use of higher sampling rates is made. The lossless compression performance is demonstrated with wide-band 256 Fs recordings, and 128 and 64 Fs down converted versions of these, demonstrating the scalability of the algorithm.

Effects of sample transparency in powder diffraction

The effects of sample transparency in a powder diffraction experiment are discussed, and formulas including effects from horizontal divergence are derived. It is shown that the classical formula by Alexander [L. E. Alexander J. Appl. Phys. 21 , 126 (1950)] is only a limiting case for zero horizontal divergence. It is also shown that in some cases extinction effects can play a role. The impact of these effects on both the line profile as well as the integrated intensity and experiments illustrating these phenomena, are discussed.

POWER MANAGEMENT OPTIONS FOR AmI APPLICATIONS

An overview of power management (PM) for ambient intelligence (AmI) applications will be presented. The basic principles of one the most important blocks in PM, the DC:DC converter, will be demonstrated, followed by a discussion of how dedicated, seamless integration of PM with specific applications, such as transmitter power amplifiers anddigitalcores,couldleadtoasubstantialsystemefficiencyimprovement.Asoneofthekey driving forces in AmI is presented by the required miniaturization, attention will be paid to the hurdles that need to be overcome in PM to realize this miniaturization. The power source in AmI applications is extremely important, and the relation between various energy scav- engers and their interaction with the PM electronics is discussed extensively. Finally, conclu- sions on power management and energy scavenging for AmI applications are presented.

A 128f/sub s/ multi-bit /spl Sigma//spl Delta/ CMOS audio DAC with real-time DEM and 115dB SFDR

A continuous-time 5b /spl Sigma//spl Delta/ audio DAC operates at 5.65MS/s (128f/sub s/). SFDR of -115dB and noise of -119dB (unweighted) are achieved by realtime DEM that cancels mismatch completely in each sample. Chip area is 2mm/sup 2/ in a 0.18/spl mu/m, thick oxide 3.3V CMOS process. Total power consumption is 150mW.