Abstract
A detailed comparative experimental and theoretical study of nonlinear distortion in laser diodes is undertaken to provide practical proving of the effectiveness and utility of the Volterra series method. The observed harmonic and intermodulation distortion levels are compared with the results given by the Volterra series nonlinear laser model using intrinsic parameters extracted from reflection and small-signal frequency response measurements. Second-harmonic, two-tone and three-tone intermodulation distortion data are all found to be in good agreement with the theoretical results, providing endorsement of the Volterra series approach for the study of distortion in microwave subcarrier optical systems. © IEE, 1996.

Abstract
An efficient algorithm for dynamically multiplexing MPEG2 encoded video sources is presented. Sources are grouped into classes regarding different combined levels of spatial detail and amount of movement. Simulations were performed using different associations of sources belonging to distinct classes, different bit rates and GOP structures. The implications associated to a real implementation are analyzed and a modular architecture is proposed. Simulation results are presented and discussed, showing that sequences with higher spatial detail and motion are those which exhibit the higher quality improvements. These results are almost not affected by the non alignment, at GOP level, between video sequences.

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.