This paper describes a new model for the stability analysis of low-pass Sigma-Delta modulators (Σ∆Ms) using the describing function method. The transfer of a single-bit quantizer is represented by a global signal gain and a phase uncertainty. This phase uncertainty arises from the limited accuracy in time with which the quantizer can detect the quantization-level crossings. This new model allows for a better prediction of possible idle patterns (important for the in-band signal-to-quantization error ratio), and calculation of zero-input stability boundaries for loop-filter parameters in higher order low-pass Σ∆Ms.

This paper describes a method of analysing words through morphological decomposition when the lexicon is incomplete. The method is used within a text-to-speech system to help generate pronunciations of unknown words. The method is achieved within a general morphological analyser system using Koskenniemi twolevel rules.

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In recent years, the knowledge engineering community has begun to explore formal specification languages as a tool in the development of knowledgebased systems. These formal knowledge modelling languages have a number of advantages over informal languages, such as their precise meaning and the possibility to derive properties through formal proofs. However, these formal languages also suffer from problems which limit their practical usefulness: they are often not expressive enough to deal with real world applications, formal models are complex and hard to read, and constructing a formal model is a difficult, error prone and expensive process. The goal of the study presented in this paper is to investigate the usability of one such formal KBS modelling language, called (ML) 2. (ML) 2 is strongly based on the structure of the knowledge-models used in the KADS KBS development method. We first designed a set of evaluation criteria. We then applied (ML) 2 in two case-studies and scored the language on our evaluation criteria. (ML) 2 scored well on most of our criteria. This leads us to conjecture that the close correspondence between the informal KADS models and the formal (ML) 2 models avoids some of the problems that traditionally plague formal specification languages.