Efficient use of frequencies in terrestrial ISDB system

Requirements for a terrestrial ISDB system and the schemes for efficiently using frequencies to fulfil the requirements are discussed. One requirement of a terrestrial ISDB system is the efficient allocation of frequencies using a SFN (single frequency network). The SFN incorporates the great advantages of OFDM, which has excellent performance under multi-path conditions. The transmission characteristics of 64QAM-OFDM and the SFN capability using 64QAM-OFDM in the Kanto area, including the Tokyo metropolitan area, are analyzed. The results show that more than a 97% coverage ratio can be obtained even by using a single channel while the same area is covered currently by more than 30 analog channels. The other requirement is a scheme for efficiently using the available frequency band for various services. A transmission scheme concept called BST-OFDM (band segmented transmission-orthogonal frequency division multiplexing) is proposed as a transmission scheme for meeting the requirements of a terrestrial ISDB system. In the BST-OFDM scheme, data are transmitted in a number of OFDM blocks called a BST-segment, for which channel coding and modulation schemes can be independently defined to provide robustness in the transmission environment according to stationary, portable and mobile reception     

Current-mode class AB design using floating voltage-source

A basis for class AB operation of current-mode CMOS circuits is presented. This has led to a new CMOS class AB current conveyor suitable for VLSI implementation. The CCII has a low input resistance with a variation of only 10% over the whole linear range     

On the capacity of packet reservation multiple access with capturein personal communication systems

A new Markovian model is developed to analyze the packet reservation multiple access (PRMA) protocol over Rician fading channels with lognormal shadowing. The packet dropping probability and the voice user capacity are defined as the performance measures. A new formula is derived to evaluate the dropping probability in the fading environment. The analytical results from our new formula show close agreement with those from computer simulations. The capture effect on the PRMA system performance is also studied. We found that, with capture, the user capacity will be improved and the service quality will degrade gracefully when the number of active users in the system increases. Using the dropping probability as the criterion, we also determine the optimal permission probability in a microcellular environment     

A novel soft-switching full-bridge DC/DC converter: analysis,design considerations, and experimental results at 1.5 kW, 100 kHz

The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM (pulsewidth modulated) full-bridge DC/DC converter substantially reduces the switching losses of the transistors and the rectifier diodes, under all loading conditions. The authors give analyses, practical design considerations, and experimental results for a 1.5 kW converter with 60 V, 25 A output, operating at 100 kHz clock frequency and 95% efficiency     

Full-wafer technology-A new approach to large-scale laserfabrication and integration

A concept for full-wafer processing (FWP) and full-wafer testing (FWT) for semiconductor laser fabrication in the AlGaAs-GaAs material system is presented. The approach is based on chemically assisted ion beam etching for the laser-mirror formation. Record values for mirror scattering, optimum mirror reflectivity, and equivalence to cleaved mirrors in terms of laser threshold and efficiency have been achieved. Promising results for uniformity and reproducibility for major laser diode characteristics on processed 2-in wafers have been found. The FWP technology has been extensively used for designing test sites to determine various materials, process, and laser parameters, such as sheet resistance, ridge dimensions, lithographic alignment errors, mirror surface leakage, etc     

Coupled-cavity passive mode-locked injection laser

Experimental results on the observation of the self-initiating passive mode-locking operation of an injection laser with a nonlinear external-coupled-cavity configuration are presented. Michelson and Fabry-Perot cavity arrangements with similar laser diodes as both the gain medium and nonlinear element have been investigated. This technique can be used for generating short pulses with ultrahigh repetition rates without utilizing both high-modulation bandwidth laser diodes and ultrafast electronics, which do not require special saturable absorbers.<>     

Proton-exchanged optical waveguides in LiNbO/sub 3/ using octanoic acid

Low-loss proton-exchanged planar waveguides in z-cut LiNbO/sub 3/ were fabricated and characterized optically using octanoic acid as a proton source. The waveguide exhibited a step-index profile with an index change of 0.118 measured at 0.633 mu m. The lowest waveguide propagation loss measured was 1.2 dB/cm, and it was reduced further to 0.4 dB/cm after annealing. The diffusion rate and the activation energy using this acid were found to be lower than those reported using other acids.<>     

Novel four quadrant DC-link soft switching inverter generating sinusoidal waveforms

A novel high frequency resonant link inverter using zero-voltage switching (except for one device where zero-current switching is used) operable in four quadrants is proposed. It provides several excellent advantages over the conventional resonant link inverters, such as low VA ratings, low acoustic noise and low harmonic distortion.<>     

Supply voltage design tradeoffs between speed and NMOSFETreliability of half-micrometer BiCMOS gates

Voltage supply scaling for a BiCMOS gate was investigated experimentally and analytically. For half-micrometer technology, the supply voltage design tradeoffs between propagation delay and NMOSFET reliability were studied. It was found that the minimum BiCMOS operating voltage ranges from 2.5 to 3.0 V. This minimum can be explained by the sum of twice the base-emitter potential and the NMOSFET threshold voltage, due to the emitter grounded Bi-MOS structure of the BiCMOS gate. As a result, 3.3-V operation is inherently marginal for BiCMOS gates. On the other hand, NMOS reliability in the BiCMOS gate is drastically improved because effective drain voltage is reduced by the base-emitter potential. Thus, NMOSFETs with a channel length shorter by more than 0.2 μm can be used, and this ensures reliable operation of BiCMOS gates at 5 V. In terms of the tradeoffs between gate speed and NMOS reliability, it is verified that BiCMOS gates offer the highest speed in half-micrometer design