A signal-to-noise enhancer with a bandwidth that is six times as wide as that of the conventional type is presented. A new circuit construction, the combination of two MSSW filters which have the same insertion loss in the broadband and two 90 hybrids, is effective to remarkably extend the bandwidth. The enhancement of the enhancer amounts to 20 dB in the operating frequency range of 1.9 GHz150 MHz in 0 to 60 degrees centigrade. This enhancer has accomplished FM threshold extension because the S/N is improved by 1 to 7 dB below the C/N of 9 dB. It was demonstrated that this new enhancer is effective for noise reduction in practical DBS reception.

Various approaches on optical network systems using wavelength-division multiplexing (WDM) technique have been proposed. It is difficult to make a scale of WDM network larger since a number of the optical wavelength which can be used is limited. In order to make easily larger scale of network, multi-hop WDM network have been proposed. We have studied 2-hop network: RookNet which has simple routing algorithm and high network throughput. Nodes in RookNet are divided into row groups and column groups and are placed in a mesh form. Packets are transferred between nodes over 1-hop or 2-hops. The 2-hop transfer means that a source node sends packets to a destination node via a relay node. When 2-hop traffic increases, relay processing time in a relay node is increasing. This is the reason that network throughput becomes low. To solve this problem is very important. In this paper, we show RookNet rearrangement algorithm which replaces location of node within group so as to decrease the 2-hop traffic and to maintain high network throughput. Proposed rearrangement algorithm can achieve improvement of 10 percent in terms of throughput. We also propose RookNet configuration which discriminates optical wavelength and subcarrier effectively in order to decrease the relay processing time.

This paper describes reverse modulation carrier recovery with a tank-limiter for Offset QPSK (OQPSK) burst signals. Acquisition performance is discussed taking into account hardware implementation errors in the carrier recovery circuit. The results indicate hardware implementation errors cause a significant recovered carrier phase error during BTR (Bit Timing Recovery) of OQPSK burst signals. A phase error reduction technique by modifying the BTR code for OQPSK burst signals is proposed to improve the acquisition performance. Computer simulation and hardware experiments confirmed its improvement. The performance of a prototype OQPSK burst demodulator using the proposed carrier recovery scheme is also presented.

Carrier mobility is one of the most fundamental parameters in semiconductor device modeling, and many mobility models have already been reported. Especially for numerical device simulators, many local models which are functions of impurity concentration and electric field at each local point have been studied. However, concerning their dependence on impurity concentration including carrier screening effects, these models suffer parameter fitting procedure because of their empirical formulation. In such models, carrier screening effects to the Coulomb potential of ionized impurity are not sufficiently considered, although we can find some models which treat the effects as only a small perturbation term. According to the simple theory of Brooks and Herring, carrier screening effects should be included in strong combination with impurity concentration terms and cannot be treated as additional perturbations. Although Brooks-Herring theory is successful, it also suffers from overestimation of the mobility values at concentration higher than 1018 cm-3 which causes some other complicated phenomena. Therefore there have been no models which directly use Brooks-Herring formula. But it is true that such screening effects should be considered when carrier concentration differs from impurity concentration as in the inversion layers of MOSFETs. We have developed a new mobility model for its dependence of impurity and carrier concentration based on the theory of Brooks-Herring. Brooks-Herring theory is based on simple physics of screened Coulomb potential, and therefore makes the model to include effects of free carriers without an artifitial formula. For high doping regime, an additional term has been introduced in Brooks-Herring formula to correct the high doping effects. Except for this term, the model should be most appropriate for including the carrier screening effects upto the concentration of 1018 cm-3. The new model is implimented in a device simulator, and is applied to the evaluation of MOSFETs especially for the universal curves of inversion layer mobility. Moreoever, the applications to the depletion-type MOSFET confirm the validity of the screening effects. The purpose of this paper is to propose the new mobility model and to show its validity through these applications to MOSFETs.

Surface-channel PMOSFETs are suitable for use in the quarter micron CMOS devices. For surface-channel PMOSFETs with p+ poly-Si gates, boron penetration and hot-carrier effects were investigated. When the annealing temperature is higher and the gate oxide is thinner, a larger threshold voltage shift was observed for p+ poly-Si PMOSFETs, because of boron penetration. Furthermore, PMOSFETs with BF2-implanted gates cause larger boron penetration than those with Boron-implanted gates. Howerer, the PMOSFET lifetime, determined by hot-carrier reliability, does not depend on the degree of boron penetration. Instead, it depends on doping species, that is, BF2 and Boron. PMOSFETs with BF2-implanted gates have about 100 times longer lifetime than those with Boron-implanted gates. The main reason for the longer lifetime of BF2-doped PMOSFETs is the incorporation of fluorine in the gate oxide of the PMOSFET with the BF2-implanted gate, resulting in the smaller electron trapping in the gate oxide. The maximun allowed supply voltage,based on the hot-carrier reliability, is higher than4V for sub-half micron PMOSFETs with BF2- or Boron-implanted poly Si gates.

This paper presents a fully digital high speed (60 Mb/s) Quadrature Phase Shift Keying (QPSK)/Offset QPSK (OQPSK) burst demodulator for radio applications, which has been implemented on a 0.5 µm Complementary Metal Oxide Semiconductor (CMOS) master slice Very Large Scale Integrated circuit (VLSI). The developed demodulator VLSI eliminates analog devices such as mixers, phase-shifters and Voltage Controlled Oscillator (VCO) for bit-timing recovery, which are used by conventional high-speed burst demodulators. In addition to the fully digital implementation, the VLSI achieves fast carrier and bit-timing acquisition in burst modes by employing a reverse-modulation carrier recovery scheme with a wave-forming filter for OQPSK operation, and a bit-timing recovery scheme with bit-timing estimation and interpolation using a pulse-shaping filter. Results of performance evaluation assuming application in Time Division Multiple Access (TDMA) systems show that the developed VLSI achieves excellent bit-error-rate and carrier-slipping-rate performance at high speed (60 Mb/s) with short preamble words (less than 100 symbols) in low Eb/No environments.

This paper proposes a new burst coherent demodulator that improves transmission quality of microcellular TDMA/TDD systems for personal communications and has configuration suitable for low power consumption with LSIC-implementation. To achieve the better transmission quality, the proposed demodulator employs coherent detection with a unique carrier recovery scheme that can operate without any preamble for carrier recovery. In addition, the demodulator uses a clock recovery scheme with clock phase estimation using twice differentiation, which eliminates hangup and attains fast clock acquisition at 2 samples/symbol. Experimental results clarify the superiority of the proposed coherent demodulator for microcellular TDMA/TDD systems. The proposed coherent demodulator reduces the irreducible frame error rate by 40%, and achieves 4dB improvement at the frame error rate of 10% compared with differential detection under the Rayleigh fading (fD/fs=810-5, τrms/Ts=510-2) typical of personal communication environments.

This paper examines a novel digital modulation/multiple access technique called Multi-Carrier Code Division Multiple Access (MC-CDMA) where each data symbol is transmitted at multiple narrowband subcarriers. Each subcarrier is encoded with a phase offset of 0 or π based on a spreading code. Analytical results are presented on the performance of this modulation scheme in an indoor wireless multipath radio channel.

A novel analysis method of the intermodulation (IM) and the noise power ratio (NPR) of multiple-carrier amplifiers is descrided. This method, based on Discrete Fourier Transform, allows an accurate calculation of IM and NPR of the amplifier having multiple carriers by directly using measured single-carrier amplitude and phase characteristics. This method has an outstanding feature in that it can be applied to the general case of n carriers having an arbitrary power level as long as frequency-dependence of amplitude and phase characteristics is negligibly small. Applying this method to the linearized amplifier, a good agreement between measured and calculated results for IM3, IM5, and NPR has been obtained for operation from linear up to saturation, which shows this method would be a good candidate for calculating IM and NPR of multiple-carrier amplifiers.

The paper proposes a new multicarrier 16QAM system for high-quality and high-bit-rate transmission with high spectral efficiency in land mobile radio communications. The proposed system uses a multicarrier transmission scheme to provide immunity against frequency-selective fading distortion. It also uses pilot-symbol-aided 16QAM to increase spectral efficiency, and it combines space diversity and FEC with maximum likelihood decoding to improve the bit error rate (BER) performance. Computer simulation shows that a BER of less than 10-4 is obtained over frequency-selective fading channels with rms delay spread of less than 5.4µs. Using a bandwidth of 200kHz the proposed system can achieve high-quality transmission with a total information rate of 256kbit/s.

When intermetal oxide film which contains much water deposited on MOSFET, degradation of hot carrier characteristics is enhanced. This mechanism is considered to be as follows. During the annealing process water is desorbed from the intermetal oxide. The desorbed water reaches the MOSFET and eventually hydrogens terminate silicon dangling bonds in the gate oxide. This paper describes a new approach which uses ESR to analyze this mechanism. The ESR measurement of number of the silicon dangling bonds in undoped polysilicon lying under the intermetal oxide shows that water diffuses from intermetal oxide to MOSFET during the annealing process. The water diffusion is blocked by introduction between the polysilicon and the intermetal oxides of P-SiN layer or CVD SiO2 damaged by implantation.

A new evaluation technique of hot carrier degradation is proposed and applied to practical evaluation of p-channel polycrystalline silicon thin film transistors (TFT). The proposed technique introduces emission microscopy which is particularly effective for evaluating TFT devices. We have developed an automatic measurement system in which measurement of the electrical characteristics and monitoring the photo emission are done simultaneously. Using this system, we have identified the dominant mechanism of hot carrier degradation in TFTs, and evaluated the effect of plasma hydrogenation on hot carrier degradation.

Optical and electrical measurements of thin film n-channel SOI-MOSFETs reveal that the exponential tail in photon emission spectra originates from electron-hole recombination. Bremsstrahlung radiation model as a physical mechanism of photon emission was experimentally negated. Negative threshold voltage shift at the initial stage of high field stress is found to be caused by hole trapping in buried oxide. Subsequent turnover characteristics is explained by a competing process between electron trapping in the front gate oxide and hole trapping in the buried oxide. As to the degradation of transconductance, generated surface state as well as trapped holes in the buried oxide which reduce vertical electric field in SOI film are involved in the complicate degradation of transconductance.

Water desorption from interlayer dielectric, spin-on-glass and SiO2 film deposited with tetraethylorthosilicate and O3, was controlled in order to reduce MOSFET hot-carrier degradation by using plasma SiO2 film as a water blocking layer. Two kinds of plasma SiO2 film were used in this study: SiH4 plasma SiO2 film deposited with SiH4 and N2O, and TEOS plasma SiO2 film deposited with TEOS and O2. Thermal desorption spectroscopy was used to study water desorption. Reduction of water desorption was obtained using plasma SiO2 film with water blocking ability; this reduction of water desorption resulted in suppression of the MOSFET hot-carrier degradation. The water blocking ability was obtained by low pressure deposition for SiH4 plasma SiO2 and low flow rate ratio of TEOS to O2 deposition for TEOS plasma SiO2. Water absorption studies of plasma SiO2 film using Fourier transform infrared spectroscopy revealed that water blocking ability is associated with small amount of water absorption both in SiH4 plasma SiO2 film and in TEOS plasma SiO2 film. Consequently, it is considered that the water blocking ability, as well as water absorption, of plasma SiO2 film depends on porosity.

This paper proposes a buried-LATID structure featuring a peaked vertical profile around gate edge for the n- drain unlike the reported conventional LATID structure. As compared to the conventional LATID FETs, the deep-submicron buried-LATID FETs achieve improved circuit speed by 7% (50% compared to LDD FETs) due to suppressed gate-to-drain capacitance and improved lifetime by 10 times (300 times compared to LDD FETs). The buried-LATID FETs are very promising for deep-submicron MOSFETs to achieve improved performance and hot-carrier reliability at the same time.

In order to construct a high-capacity and high-reliable indoor wireless communications system, it is essential to design the modulation/demodulation, coding and access schemes with high and variable data rate transmission capabilities, which meet the technical requirements inherent to wireless communications, i.e., high frequency utilization efficiency and robustness for fading. In this paper, we propose the frequency and time division multiple access with demand-assignment (FTDMA/DA) using multicarrier modulation as a frequency and time synchronous answer to meet the requirements, and analyze the performance of the FTDMA/DA system, taking account of teletraffic characteristics of multimedia information sources.

A two-dimensional photoemission analysis of hot-carrier effects in LOCOS- and trench-isolated CMOS devices with channel width ranging from 160 µm to 0.2 µm is described. Photoemission-intensity profiles can be measured in spatial resolution of 0.1 µm. Different photoemission characteristics are observed in n-MOSFETs depending on isolation technology; M-shaped photoemission-intensity profiles are observed as gate voltage becomes higher in trench-isolated ones, but scarcely measured in LOCOS-isolated ones. As for p-MOSFETs, similar characteristics are observed independent on isolation technology and slightly M-shaped profiles are observed at higher gate voltages. The recession of 0.1-0.2 µm in photoemission area from the gate electrode edge due to gate bias dependence of the pinch-off points of n--LDD drain is observed when gate voltage increases from 1 V to 6 V. Meanwhile the recession of the pinch-off points in p-MOSFETs is less than 0.1 µm even when gate voltage increases from 2 V to 8 V. A qualitative explanation for the experimental results is given for four kinds of MOSFETs in comparing each device structure near the isolation edge.

This paper presents a potential FM double modulation technique for subcarrier optical transmission in order to improve the input dynamic range. The proposed theory of FM double modulation is presented. The BER performance and input dynamic range are shown theoretically and experimentally compared with conventional direct intensity modulation. It was found that the dynamic range could be experimentally improved by 20dB compared with the conventional method by using FM double modulation. The proposed technique achieved an input dynamic range of 60 dB even when using a commercial Fabri-Perot LD.

Atmospheric optical communication (AOC) system using subcarrier PSK modulation is proposed and its superiority to OOK modulation in the presence of scintillation is discussed theoretically. An experimental AOC setup with a subcarrier modulated by 155.52(Mb/s) DPSK at light wave-length λ=0.83(µm) over an 1.8(km) outdoor path is employed to show the performance. Theoretical and experimental results are compared under scintillation in clear weather and a good agreement is observed. Finally, AOC systems using subcarrier M-ary PSK and multiple subcarriers are proposed and discussed.

This paper describes an overview of wireless communications based on fiber-radio technologies from the viewpoint of system applications, particularly in the area of microcell radio systems. Feasible fiber-radio networks design are detailed in order to increase system performance and cost effectiveness. The benefits of the evolving fiber-radio microcell system are discussed with a spectral delivery scheme to meet traffic demands. Foreseeable electronic and optic technologies are reviewed in light of the key parameters to optimize the overall system. This strategy will play a role in broadband and flexible networks.