To reduce the gate leakage current of AlGaN/GaN HEMTs, we selected ITO/Ni/Au for Schottky electrodes and Schottky characteristics were compared with those of Ni/Au electrodes. ITO/Ni/Au and Ni/Au electrodes were deposited by vacuum evaporation and annealed at 350 in nitrogen atmosphere. From the I-V evaluation results of ITO/Ni/Au electrodes, forward and reverse leakage currents were reduced. Schottky characteristics of ITO/Ni/Au electrodes were also improved compared to these of Ni/Au electrodes. In addition, substantial decrease of leakage currents was confirmed after the annealing of HEMTs with ITO/Ni/Au electrodes. This may be explained that ITO/AlGaN interface state became lower by the annealing. By the temperature dependence of I-V curves, clear dependence was confirmed for the gates with ITO/Ni/Au electrodes. On the other hand, small dependence was observed for those with Ni/Au electrodes. From these results, tunnel leakage currents were dominant for the gates with Ni/Au electrode. Thermal emission current was dominant for the gates with ITO/Ni/Au electrode. The larger temperature dependence was caused that ITO/AlGaN interface states were smaller than those for Ni/Au electrode. It was suggested that suppressed AlGaN Schottky barrier thinning was caused by the surface defect donors, then tunneling leakage currents were decreased. We evaluated HEMT characteristics with ITO/Ni/Au electrode and Ni/Au electrode. Id max and Gm max were similar characteristics, but Vth with ITO/Ni/Au electrode was shifted +0.4 V than that with Ni/Au electrode due to the higher Schottky barrier. It was confirmed to have a good pinch-off currents and low gate leakage currents by ITO/Ni/Au electrodes.

This paper reviews techniques for digitally assisted pipeline ADCs. Errors of pipeline ADCs originated by capacitor mismatch, finite amplifier gain, incomplete settling and offset can be corrected in digital-domain foreground or background calibrations. In foreground calibrations, the errors are measured by reconfiguration of the building blocks of pipeline ADC or using an INL plot without reconfiguration. In background calibrations, the errors are measured with random signal and continuously corrected while simultaneously performing the normal A/D conversions. Techniques for measuring and correcting the errors at foreground and background are reviewed and a unified approach to the description of the principle of background calibration of gain errors is presented.

Auditory artifacts due to switching head-related transfer functions (HRTFs) are investigated, using a software-implemented dynamic virtual auditory display (DVAD) developed by the authors. The DVAD responds to a listener's head rotation using a head-tracking device and switching HRTFs to present a highly realistic 3D virtual auditory space to the listener. The DVAD operates on Windows XP and does not require high-performance computers. A total system latency (TSL), which is the delay between head motion and the corresponding change of the ear input signal, is a significant factor of DVADs. The measured TSL of our DVAD is about 50 ms, which is sufficient for practical applications and localization experiments. Another matter of concern is the auditory artifact in DVADs caused by switching HRTFs. Switching HRTFs gives rise to wave discontinuity of synthesized binaural signals, which can be perceived as click noises that degrade the quality of presented sound image. A subjective test and excitation patterns (EPNs) analysis using an auditory filter are performed with various source signals and HRTF spatial resolutions. The results of the subjective test reveal that click noise perception depends on the source signal and the HRTF spatial resolution. Furthermore, EPN analysis reveals that switching HRTFs significantly distorts the EPNs at the off signal frequencies. Such distortions, however, are masked perceptually by broad-bandwidth source signals, whereas they are not masked by narrow-bandwidth source signals, thereby making the click noise more detectable. A higher HRTF spatial resolution leads to smaller distortions. But, depending on the source signal, perceivable click noises still remain even with 0.5-degree spatial resolution, which is less than minimum audible angle (1 degree in front).

Impacts of electromagnetic (EM) interference (immunity) on operation of LSI circuits in a QFP-packaged and PCB-mounted environment are studied. EM power injection to a power-supply system leads to malfunction, where the power is translated into voltage bounces through combined on- and off- chip impedances, affecting power supply and ground, as well as signal nodes in a die, seen from on-chip waveform measurements. A lumped power-supply impedance model and the minimum amplitude of voltage bounce induced by EM power for malfunction, both of which can be derived from external measurements to a given packaged LSI, formulate an EM interference model that is helpful in the PCB design toward high immunity. The technique can be generally applied to systems-on-chip applications.

A cross-coupled charge pump with internal pumping capacitor, which is advantageous from a point of minimizing TFT-LCD driver IC module, is newly proposed in this paper. By using NMOS and PMOS diodes connected to boosting nodes from VIN nodes, the pumping node is precharged to the same value at the pumping node in starting pumping. Since the first-stage charge pump is designed differently from the other stage pumps, a back current of pumped charge from charge pumping node to input stage is prevented. As a pumping clock driver is located in front of pumping capacitor, the driving capacity is improved by reducing a voltage drop of the pumping clock line from parasitic resistor. Finally, a layout area is decreased more compared with the conventional cross-coupled charge pump by using a stack-MIM capacitor. A proposed charge pump for TFT-LCD driver IC is designed with 0.13 µm triple-well DDI process, fabricated, and tested.

Recent advancements in the ubiquitous sensor network field have brought considerable feasibility to the realization of a ubiquitous society. A ubiquitous sensor network will enable the cooperative gathering of environmental information or the detection of special events through a large number of spatially distributed sensor nodes. Thus far, radio frequency identification (RFID) as an application for realizing the ubiquitous environment has mainly been developed for public and industrial systems. To this end, the most existing applications have demanded low-end antennas. In recent years, interests of ubiquitous sensor network have been broadened to medical body area networks (BAN), wireless personal area networks (WPAN), along with ubiquitous smart worlds. This increasing attention toward in ubiquitous sensor network has great implications for antennas. The design of functional antennas has received much attention because they can provide various kinds of properties and operation modes. These high-end antennas have some functions besides radiation. Furthermore, smart sensor nodes equipped with cooperated high-end antennas would allow them to respond adaptively to environmental events. Therefore, some design approaches of functional antennas with sensing and reconfigurability as high-end solution for smart sensor node, as well as low-end antennas for mobile RFID (mRFID) and SAW transponder are presented in this paper.

For battery-powered electronic products, one way to extend battery life is to use a versatile step-up/step-down DC-DC converter. A new versatile step-up/step-down switched-capacitor-based converter structure is proposed, and its efficiency is analyzed. In the step-down case, the efficiency is the same as, or even better than the efficiency of linear regulators.

It is important to monitor routing protocols to ensure IP networks and their operations can maintain sufficient level of stability and reliability because IP routing is an essential part of such networks. In this paper, we focus on Open Shortest Path First (OSPF), a widely deployed intra-domain routing protocol. Routers running OSPF advertise their link states on Link State Advertisements (LSAs) as soon as they detect changes in their link states. In IP network operations, it is important for operators to ascertain the location and type of a failure in order to deal with failures adequately. We therefore studied IP network failure identification based on the monitoring of OSPF LSAs. There are three issues to consider in regard to identifying network failures by monitoring LSAs. The first is that multiple LSAs are flooded by a single failure. The second is the LSA delay, and the third is that multiple failures may occur simultaneously. In this paper, we propose a method of network failure identification based on a detailed analysis of OSPF LSA flooding that takes into account the above three issues.

In this letter, we propose a shared adaptive packet loss concealment scheme for the high quality guaranteed Internet telephony service which connects multiple users. In order to recover packet loss efficiently in the all-IP based convergence environment, we provide a robust signal recovery scheme which is based on the shared adaptive both-side information utilization. This scheme is provided according to the average magnitude variation across the frames and the pitch period replication on the 1-port gateway (G/W) system. The simulated performance demonstrates that the proposed scheme has the advantages of low processing times and high recovery rates in the all-IP based ubiquitous environment.

This study is to investigate new schemes for distributing cryptographic keys in sensor networks. Sharing a key is the very first step to realize secure communication over an untrusted network infrastructure, but commonly used cryptographic techniques cannot be employed for sensor networks due to the restriction of computational resources of sensor nodes. A practical solution to this issue is to predistribute cryptographic keys in sensor nodes before they are deployed. A focal point in this solution is the choice of keys that are assigned to a sensor node. Eschenauer et al. considered to choose keys randomly, and Chan et al. also followed the random choice approach. We consider in this paper a new approach in which keys are assigned according to a basic algebraic geometry. The performance of the proposed scheme is investigated analytically.

With the multiplication of attacks against computer networks, system administrators are required to monitor carefully the traffic exchanged by the networks they manage. However, that monitoring task is increasingly laborious because of the augmentation of the amount of data to analyze. And that trend is going to intensify with the explosion of the number of devices connected to computer networks along with the global rise of the available network bandwidth. So system administrators now heavily rely on automated tools to assist them and simplify the analysis of the data. Yet, these tools provide limited support and, most of the time, require highly skilled operators. Recently, some research teams have started to study the application of visualization techniques to the analysis of network traffic data. We believe that this original approach can also allow system administrators to deal with the large amount of data they have to process. In this paper, we introduce a tool for network traffic monitoring using visualization techniques that we developed in order to assist the system administrators of our corporate network. We explain how we designed the tool and some of the choices we made regarding the visualization techniques to use. The resulting tool proposes two linked representations of the network traffic and activity, one in 2D and the other in 3D. As 2D and 3D visualization techniques have different assets, we resulted in combining them in our tool to take advantage of their complementarity. We finally tested our tool in order to evaluate the accuracy of our approach.

To provide the distance information of a sound source in virtual audio space, we must have some information about effective distance cues and there must be some way to handle them properly. It is well known that the conventional cues comprise loudness, spectral information, reverberation and binaural information. Some research works have shown that most of these cues can give listeners only limited distance information. Among these cues, reverberation can give listeners effective distance information, but the implementation using this cue is not a simple problem because there are no well-defined parameters and methods. This paper discusses methods to control the perceived auditory depth with the reverberation cue. A two-stepped linear envelope method and an artificial reverberator, which can control the early reflection slope of an impulse response but does not alter the reverberation time, are proposed as solutions. To validate these methods, subjective assessment was performed.

This paper proposes novel feedforward architecture of the second-order multibit ΔΣAD modulator with single DAC-feedback topology. The ΔΣAD modulator realizes high resolution by oversampling and noise shaping techniques. However, its SNDR (Signal to Noise and Distortion Ratio) is limited by the dynamic range of the input signal and non-idealities of circuit building blocks, particularly by the harmonic distortion in amplifier circuits. A full feedforward ΔΣAD modulator structure has the signal transfer function of unity under ideal circumstances, which means that the signal swings through the loop filter become smaller compared with a feedbacked ΔΣAD modulator. Therefore, the harmonic distortion generated inside the loop filter can be significantly reduced in the feedforward structure because the effect of non-idealities in amplifiers can be suppressed when signal swing is small. Moreover, the reduction of the internal signal swings also relaxes output swing requirements for amplifiers with low supply voltage. However, in conventional feedforward ΔΣAD modulator, an analog adder is needed before quantizer, and especially in a multibit modulator, an additional amplifier is necessary to realize the summation of feedforward signals, which leads to extra chip area and power dissipation. In this paper, we propose a novel architecture of a feedforward ΔΣAD modulator which realizes the summation of feedforward signals without additional amplifier. The proposed architecture is functionally equivalent to the conventional one but with smaller chip area and lower power dissipation. We conducted MATLAB and SPICE simulations to validate the proposed architecture and modulator circuits.

We present a model checking approach to the rationale, implementation, and applications of a query language for location-based services. Such query mechanisms are necessary so that users, objects, and/or services can effectively benefit from the location-awareness of their surrounding environment. The underlying data model is founded on a symbolic model of space organized in a tree structure. Once extended to a semantic model for modal logic, we regard location query processing as a model checking problem, and thus define location queries as hybrid logic-based formulas. Our approach is unique to existing research because it explores the connection between location models and query processing in ubiquitous computing systems, relies on a sound theoretical basis, and provides modal logic-based query mechanisms for expressive searches over a decentralized data structure. A prototype implementation is also presented and will be discussed.

Developing LSIs with EMI suppression, particularly for use in automobiles, is important for improving warranties and customer acquisition. First, we describe that the measures against EMI noise caused by a X'tal oscillator are important. Next, we present a practical method for analyzing the noise with models of the inside and outside of a chip. In addition, we propose a within-chip measure against EMI noise that takes chip cost into account. The noise is suppressed by using an appropriate resistance and capacitance on the power line. Simulation results demonstrated the method's effectiveness in suppressing noise.

Various advantages of cooperative peer-to-peer networks are strongly counterbalanced by the open nature of a distributed, serverless network. In such networks, it is relatively easy for an attacker to launch various attacks such as misrouting, corrupting, or dropping messages as a result of a successful identifier forgery. The impact of an identifier forgery is particularly severe because the whole network can be compromised by attacks such as Sybil or Eclipse. In this paper, we present an identifier authentication mechanism called random visitor, which uses one or more randomly selected peers as delegates of identity proof. Our scheme uses identity-based cryptography and identity ownership proof mechanisms collectively to create multiple, cryptographically protected indirect bindings between two peers, instantly when needed, through the delegates. Because of these bindings, an attacker cannot achieve an identifier forgery related attack against interacting peers without breaking the bindings. Therefore, our mechanism limits the possibility of identifier forgery attacks efficiently by disabling an attacker's ability to break the binding. The design rationale and framework details are presented. A security analysis shows that our scheme is strong enough against identifier related attacks and that the strength increases if there are many peers (more than several thousand) in the network.

A sound localization method in the proximal region is proposed, which is based on a low-cost 3D sound localization algorithm with the use of head-related transfer functions (HRTFs). The auditory parallax model is applied to the current algorithm so that more accurate HRTFs can be used for sound localization in the proximal region. In addition, head-shadowing effects based on rigid-sphere model are reproduced in the proximal region by means of a second-order IIR filter. A subjective listening test demonstrates the effectiveness of the proposed method. Embedded system implementation of the proposed method is also described claiming that the proposed method improves sound effects in the proximal region only with 5.1% increase of memory capacity and 8.3% of computational costs.

The MOS switch with bootstrapped technique is widely used in low-voltage switched-capacitor circuit. The switched-capacitor circuit with the bootstrapped technique could be a dangerous design approach in the nano-scale CMOS process due to the gate-oxide transient overstress. The impact of gate-oxide transient overstress on MOS switch in switched-capacitor circuit is investigated in this work with the sample-and-hold amplifier (SHA) in a 130-nm CMOS process. After overstress on the MOS switch of SHA with unity-gain buffer, the circuit performances in time domain and frequency domain are measured to verify the impact of gate-oxide reliability on circuit performances. The oxide breakdown on switch device degrades the circuit performance of bootstrapped switch technique.

Automated capture and retrieval of experiences at home is interesting due to the wide variety and personal significance of such experiences. We present a system for retrieval and summarization of continuously captured multimedia data from Ubiquitous Home, a two-room house consisting of a large number of cameras and microphones. Data from pressure based sensors on the floor are analyzed to segment footsteps of different persons. Video and audio handover are implemented to retrieve continuous video streams corresponding to moving persons. An adaptive algorithm based on the rate of footsteps summarizes these video streams. A novel method for audio segmentation using multiple microphones is used for video retrieval based on sounds with high accuracy. An experiment, in which a family lived in this house for twelve days, was conducted. The system was evaluated by the residents who used the system for retrieving their own experiences; we report and discuss the results.

This paper proposes a performance model for design of pipelined analog-to-digital converters (ADCs). This model includes the effect of overdrive voltage on the transistor, slewing of the operational amplifier, multi-bit structure of multiplying digital to analog converter (MDAC) and technology scaling. The conversion frequency of ADC is improved by choosing the optimum overdrive voltage of the transistor, an important consideration at smaller design rules. Moreover, multi-bit MDACs are faster than the single-bit MDACs when slewing occurs during the step response. The performance model of pipelined ADC shown in this paper is attractive for the optimization of the ADC's performances.