Optimal Pulsewidth Modulation for Current Source Inverters

Two different pulsewidth modulation (PWM) schemes for current source inverters (CSI) are described. The first one is based on off-line optimization of individual switching angles and requires a microprocessor for implementation and the second one uses a special subharmonic modulation and could be implemented with analog and medium-scale integration (MSI) digital circuits. When CSI's are used in ac motor drives, the optimal PWM pattern depends on the performance criteria being used, which in turn depend on the drive application. In this paper four different performance criteria are considered: 1) current or torque harmonic elimination, 2) current harmonic minimization, 3) speed ripple minimization, and 4) position error minimization. As an example a self-controlled synchronous motor (SCSM) supplied by the PWM CSI is considered. The performance of the CSI-SCSM with the optimal PWM schemes proposed herein are compared with that using a conventional 120° quasi-square wave current.     

High-speed, high-current-gain p-n-p InP/InGaAs heterojunctionbipolar transistors

p-n-p InP/InGaAs heterojunction bipolar transistors (HBTs) are reported for the first time. The transistors, grown by metal organic molecular beam epitaxy (MOMBE), exhibited maximum DC current gain values up to 420 for a base doping level of 4×10¹⁸ cm^-3 . Small-signal measurements on self-aligned transistors with 3-μm×8-μm emitter area indicated the unity gain cutoff frequency value of 10.5 GHz and the inferred maximum frequency of oscillation of 25 GHz. The results clearly demonstrate the feasibility of complementary integrated circuits in the InP material system     

Efficient Parallel Gouraud Shading and Linear Interpolation over Triangles

A parallel raster algorithm to draw Gouraud shaded triangles is presented. At the heart of the algorithm is a new constrained parallel edge-traversal technique. This parallel traversal represents an increased level of parallelism compared to the existing solutions. Next, traditional algorithms take different amounts of time to advance from one horizontal span to another for the left edge and the right edge of the triangle when the slope of one of the edges is more than one and that of the other edge is less than one. This causes one processor to wait for another processor. The parallel constrained edge traversal technique removes this problem by directly jumping from one span to the next. It also ensures that adjacent triangles that share an edge do not share any pixels. Moreover, no cracks occur between adjacent polygons. Unlike some existing algorithms whose complexity depends on the size of the bounding box of the triangle, the complexity of our algorithm is solely dependenton the perimeter and area of the triangle. Due to the above features, the algorithm presented here exposes a greater degree of parallelism at considerably lesser cost and achieves better processor utilization, compared to existing algorithms for this problem^{1, 2, 3, 4, 5, 6}. The algorithm is well suited for hardware implementation.     

Multiplication noise of wide-bandwidth InP/InGaAsP/InGaAs avalanchephotodiodes

Measurements of InP/InGaAsP/InGaAs separate absorption, grading, and multiplication avalanche photodiode multiplication indicate that at high gains the excess noise factors approach values predicted by the conventional continuum theory. However, at lower gains the noise is suppressed. This is probably an artifact of the very thin multiplication layers which have been used to increase the gain-bandwidth product. From the frequency response of the noise power, a gain-bandwidth product of 60 GHz, which is consistent with the value of 57 GHz obtained directly from bandwidth measurements, is deduced     

Reliability analysis of continuous beams

The paper presents a method for the reliability analysis of continuous beams. Both the material and geometric parameters are taken as probabilistic. Initially a parametric study is carried out in the case of deterministic analysis to establish the hierarchy of the variables before undertaking the probabilistic analysis. Based upon the probabilistic analysis, the frequency distribution of different variables, such as rotations, end moments and reactions is presented for a particular problem. The study revealed that the variation of the generated set from its mean value is maximum in the case of rotations, followed by moment of inertia, end moments and reactions.     

Monolithic balanced p-i-n/HBT photoreceiver for coherent optical heterodyne communications

Two InGaAs p-i-n photodetectors connected in a balanced configuration have been monolithically integrated with a transimpedance preamplifier made from InP-InGaAs heterojunction bipolar transistors (HBTs) to realize a balanced optoelectronic integrated circuit (OEIC) receiver. The receiver, with a bandwidth of 3 GHz and a common mode rejection of 25 dB, has a sensitivity of -49 dBm at a bit error rate of 10/sup 9/ under NRZ FSK reception at 200 Mb/s.<>     

Heterojunction InP/GaInAs phototransistors/bipolar transistorsgrown by MOVPE

Heterojunction InP/GaInAs phototransistors with base terminals have been fabricated by atmospheric pressure metal organic vapour phase epitaxy. When operated as bipolar transistors, the devices exhibit high current gain (>1600) and good junction ideality factors (1.06 for the base/emitter and 1.25 for the base/collector junction). When operated as phototransistors, the devices have large optical gain (>800) at an incident power of 1 μW, at a wavelength of 1.3 μm