In Complimentary Metal Oxide Semiconductor (CMOS) circuit designs, the PMOS/ NMOS width ratio (β) is an important parameter in the design of digital circuits using conventional logic. The conventional method of estimating β considers mobility and does not take into account the effect of various technology parameters. In the paper, "Comparison of Trans-Conductance Ratio (β) for a High-Speed Inverter Design", the authors, Abhijit Asati and Chandra Shekhar propose a more accurate method of estimation of PMOS/NMOS width ratio, using several technology parameters so as to improve the inverter threshold (switching threshold) voltage by 5% and reduce average propagation delay by 0.6% for the 0.5 mm technology.

OCDMA (Optical Code Division Multiple Access) in optical fiber communication provides vast bandwidth availability, and users can access the same optical channel with less delay. It is difficult to construct codes with good auto and cross correlation properties with low Multiple Access Interference (MAI). In the paper, "Reliability of OCDMA MAN System Using Wavelength-Time Matrix Encoding and Decoding Technique", the authors, Gurjit Kaur, Divyesh Mohan Saxena and Neena Gupta, propose a reliable simulated model for OCDMA system with improved performance, as compared to previous designs. The design considers a metropolitan area network with optical fiber length of 60 km. A comparative Bit Error Rate (BER) and eye diagram analysis shows that the proposed system can accommodate 16 simultaneous users for 2.5 Gbps for bit error rate e^_10, compared to the previous designs of 1.25 Gbps for 16 users with BER e^_9. BER performance for 1 Gbps, 1.25 Gbps and 2.5 Gbps is also found to be better. And at 5 Gbps, the designed system can work for up to eight simultaneous users to provide BER less than 10^_11.

Microstrip antennas find applications in the current communication systems because of their unique properties like lightweight, ease of fabrication, low production cost, low profile, etc. Several techniques have been proposed in literature for improving the inherent disadvantage of narrow impedance bandwidth. N M Sameena, R B Konda, S N Mulgi and P V Hunagund, in their paper, "Shorted Parasitic Rectangular Microstrip Antenna for Compact Operation", propose a simple design of rectangular microstrip antenna with shorted parasitic strip for compact and wideband operation. The antenna consists of a parasitic strip, which is looped around the rectangular microstrip patch, and a shorting strip is placed at the optimum point between the parasitic strip and radiating patch. From experimental results, it is seen that a 73.97% of large effective reduction of antenna size is achieved and –10 dB return loss impedance bandwidth is 1.83 times more than that of conventional rectangular microstrip antenna without change in broadside radiation characteristics. Design concepts of proposed antennas are given and experimental results are discussed. The simple antenna can be used in Secondary Surveillance Radar (SSR) systems (1.03-1.09 GHz).

In the paper, "Simulation, Design and Development of a Wideband Printed Linearly Tapered Slot Antenna", Ved Vyas Dwivedi and Y P Kosta consider the design of a printed, Linearly Tapered Slot Antenna for 11.0 GHz, using the Stepped Approximation Method (SAM). The microstrip antenna was fabricated on Poly Tetra Fluoro Ethylene (PTFE) and finally tested for its RF wideband performance. The performance is simulated and various antenna parameters, such as Voltage Standing Wave Ratio (VSWR) radiation pattern and energy loss have been studied and optimized for wideband performance. The performance of this antenna system indicated its multi-frequency operation as a wideband Traveling Wave Antenna in the end fire mode. Also, the dielectric constant performance variation with frequency was tested to confirm the effectiveness of its wideband multi-frequency operation.

The multi-phase motor drive has found wide applications with the advent of cheap and reliable semiconductor devices such as IGBTs and MOSFETs. Five-phase and six-phase motors are studied extensively. The paper, "Performance Comparison of a Six-Phase VSI for Symmetrical and Quasi Six-Phase Configurations", by Shaikh Moinuddin and Atif Iqbal, deals with the operation of a six-phase inverter for both symmetrical and quasi six-phase output voltage configurations. The inverter operation is analyzed for 180° and 150° conduction angles. Based on the simulated and experimental results, the authors claim that the controller designed is to be simple and robust. It is also found that the proposed 150° conduction mode offers better harmonic performance, compared to the existing 180° conduction mode.

Particle Swarm Optimization (PSO) techniques are finding wide applications in the control system design. In the paper, "Dynamic Performance Improvement of Variable Speed Induction Motor Drives Using Particle Swarm Optimizer", K Naga Sujatha, K Vaisakh and K Srihari, have discussed the application of this technique to the design of the variable speed induction motor drive system using state variable control. The dynamic system performance has been found to be better than the one designed by adopting the Variable Structure Controller (VSC) method and Genetic Algorithm (GA) approach.

In the paper, "Optimal Power Flow Using Differential Evolution Under Deregulated Environment", Rathinasamy Rajathy, Gnanadass Ramachandran, K Manivannan and Harish Kumar, have studied the deregulated power system using Differential Evolution (DE) technique and compared it with Particle Swarm Optimization (PSO) technique. The optimal power flow problem has been studied using IEEE 14-bus and 30-bus systems. The proposed Differential Evolution (DE) approach is found to be better than PSO method and is capable of providing minimum solution, irrespective of the nature of the objective function.

-- M S R Murty
Consulting Editor