Abstract

Abstract
Perceptual coders have proven to be highly efficient in the context of audio or video applications involving bit rate reduction. However, this efficiency is strongly limited in very low bit rate coding conditions. This paper studies the multiplicative effects of quantization in the frequency domain, when an overlapped filter bank (TDAC) is used to shape the quantization noise in a perceptually optimal way. The associated circular convolution operation generates aliased components in the time domain that are examined and subjected to minimization. A closed form expression is suggested to approximate an optimal transform window offering a desired tradeoff between the reduction of the time artifacts produced by a coarse quantization and the reduction of the stop-band leakage, relative to other transform windows commonly used.

Abstract

Abstract
Supply current test is well established for digital CMOS circuits and the advantages of improved observability and reliability indication have prompted its use for analogue and mixed signal circuits. A short review of the literature on this subject is given. Fault simulation is used for the investigation of dynamic supply current test of a PLL, confirming existing results from smaller circuits that a combination of supply current and output voltage monitoring leads to higher fault coverage. In the paper, fault coverage is further improved, using crosscorrelation of the supply current and output signals, and the potential for BIST implementation of this technique is demonstrated using low resolution polarised crosscorrelation. Fault simulation is also performed on an analogue multiplier to investigate the effect of process parameter deviations on the supply current. The fault coverage is found to be improved by removing the DC component of the signal. Encouraging results are obtained from the application of supply current test techniques to a commercial mixed signal ASIC currently beyond the capabilities of analogue fault simulation, indicating that efforts at improving fault simulation in this area are worthwhile. The requirements for fault modelling and simulation to support supply current test are discussed and some initial results of accelerating this process using macromodelling are presented.

Abstract
The use of cross-correlation between power supply current and output voltage dynamic responses is presented as a methodology for improved mixed current/voltage testing of analogue and mixed-signal circuits. Results obtained from simulations are presented which show that better fault coverage and a simplification of test circuitry can be obtained, when compared with the results obtained from the direct observation of the individual signals. These advantages are important factors to develop viable new design for testability and built-in self test techniques.

Abstract
We show that incoherently coupled soliton pairs are possible in biased photorefractive crystals, under steady-state conditions. These solitons can propagate in bright-bright, dark-dark, as well as in bright-dark configurations. Such soliton pairs can be established provided that the carrier beams share the same polarization, wavelength, and are mutually incoherent. Relevant examples are provided where the photorefractive crystal is of the strontium barium niobate type. The characteristics and stability properties of these soliton states are also discussed in detail. (C) 1996 American Institute of Physics.