Cyclic code weight spectra and BIST aliasing

In built-in self-test for logic circuits, test data reduction can be achieved using a linear feedback shift register. The probability that this data reduction will allow a faulty circuit to be declared good is the probability of aliasing. Based on the independent bit-error model, we show that the code spectra for the cyclic code generated by the feedback polynomial can be used to obtain an exact expression for the aliasing probability of a multiple input signature register when the test length is a multiple of the cycle length. Several cases are examined and, as expected, primitive feedback polynomials provide the best performance. Some suggestions to avoid peaks in the aliasing probability are given.     

Aliasing properties of circular MISRs

In built-in self-test for logic circuits, test data reduction can be achieved using a linear feedback shift register. The probability of this data reduction allowing a faulty circuit to be declared good is the probability of aliasing. This article examines aliasing in circular multiple-input shift-registers (MISRs), under the independent bit error model. We present an exact closed form expression for aliasing probability without assuming equiprobable bit error probabilities. We show that the aliasing probability can be much larger than its asymptotic value. Irrespective of the register length we prove that for a circular MISR, when two inputs are used for testing out ofm possible inputs, high minimum spatial separations between inputs result in low aliasing probabilities. We also show that for equiprobable errors an m-bit circular MISR can be replaced with a set ofm single-bit MISRs without affecting aliasing probability or adding any additional logic, to reduce the propagation delay due to feedback path. The above features can be used as criteria for the MISR design.     

Carrier Lifetimes of Iodine-Doped CdMgTe/CdSeTe Double Heterostructures Grown by Molecular Beam Epitaxy

Iodine-doped CdMgTe/CdSeTe double heterostructures (DHs) have been grown by molecular beam epitaxy and studied using time-resolved photoluminescence (PL), focusing on absorber layer thickness of 2 μm. The n-type free carrier concentration was varied to ～7 × 10¹⁵ cm^?3, 8.4 × 10¹⁶ cm^?3, and 8.4 × 10¹⁷ cm^?3 using iodine as dopant in DHs. Optical injection at 1 × 10¹⁰ photons/pulse/cm² to 3 × 10¹¹ photons/pulse/cm², corresponding to initial injection of photocarriers up to ～8 × 10¹⁵ cm^?3, was applied to examine the effects of excess carrier concentration on the PL lifetimes. Iodine-doped DHs exhibited an initial rapid decay followed by a slower decay at free carrier concentration of 7 × 10¹⁵ cm^?3 and 8.4 × 10¹⁶ cm^?3. The optical injection dependence of the carrier lifetimes for DHs was interpreted based on the Shockley–Read–Hall model. The observed decrease in lifetime with increasing n is consistent with growing importance of radiative recombination.     

Iodine Doping of CdTe and CdMgTe for Photovoltaic Applications

Iodine-doped CdTe and Cd_1?x Mg _x Te layers were grown by molecular beam epitaxy. Secondary ion mass spectrometry characterization was used to measure dopant concentration, while Hall measurement was used for determining carrier concentration. Photoluminescence intensity and time-resolved photoluminescence techniques were used for optical characterization. Maximum n-type carrier concentrations of 7.4 × 10¹⁸ cm^?3 for CdTe and 3 × 10¹⁷ cm^?3 for Cd_0.65Mg_0.35Te were achieved. Studies suggest that electrically active doping with iodine is limited with dopant concentration much above these values. Dopant activation of about 80% was observed in most of the CdTe samples. The estimated activation energy is about 6 meV for CdTe and the value for Cd_0.65Mg_0.35Te is about 58 meV. Iodine-doped samples exhibit long lifetimes with no evidence of photoluminescence degradation with doping as high as 2 × 10¹⁸ cm^?3, while indium shows substantial non-radiative recombination at carrier concentrations above 5 × 10¹⁶ cm^?3. Iodine was shown to be thermally stable in CdTe at temperatures up to 600°C. Results suggest iodine may be a preferred n-type dopant compared to indium in achieving heavily doped n-type CdTe.     

Determining and Controlling the Magnesium Composition in CdTe/CdMgTe Heterostructures

The relationships between Mg composition, band gap, and lattice characteristics are investigated for Cd_1?x Mg _x Te barrier layers using a combination of cathodoluminescence, energy dispersive x-ray spectroscopy, variable angle spectral ellipsometry, and atom probe tomography. The use of a simplified, yet accurate, variable angle spectral ellipsometry analysis is shown to be appropriate for fast determination of composition in thin Cd_1?x Mg _x Te layers. The validity of using high-resolution x-ray diffraction for CdTe/Cd_1?x Mg _x Te double heterostructures is discussed. The stability of CdTe/Cd_1?x Mg _x Te heterostructures are investigated with respect to thermal processing.     

New traffic model for performance analysis of processor-memory multistage interconnection networks

Multistage interconnection networks (MINs) provide cost effective, high bandwidth processor-memory communication in multiprocessor systems. The authors propose a nonuniform traffic model to analyse performance of processor-memory MINs, in the presence of switch and link failures.<>