Coordination of wavelength and time-window assignment in WDM-based TDM hybrid-PONs

In passive optical networks (PONs), the low effectiveness in terms of service utilization and network evolution have been important design issues. In this article, we introduce a hybrid access network architecture, so called scalable WDM-based Ethernet hybrid-PON (SWE-PON), which features a wavelength-division-multiplexed (WDM) feeder network using a combination of tunable laser device (TLD) and cyclic arrayed waveguide grating (AWG) and time-division-multiplexed (TDM) distribution network based on a reflective transmission mode. Necessary conditions needed to guarantee flawless packet transmission through normal WDM/TDM hierarchical PONs including the SWE-PON, are analyzed. We also propose a hierarchical fair time-window allocation mechanism which coordinates wavelength assignment and time-window bandwidth allocation so that high link utilization and fair bandwidth allocation are guaranteed in every multiplexing level.

70 dB Dynamic Range CMOS Wideband Digital Variable Gain Amplifier for AGC in DVB-T/H Receivers

This paper presents a novel variable gain amplifier (VGA) design which is applied in the automatic gain control loop of digital video broadcasting (DVB) receivers designed for standards DVB-T/H. The VGA is composed of three cascaded tunable gain stages to provide a 70 dB dynamic range with 2 dB gain steps. Each gain stage is based on a digital variable gain amplifier (DVGA) which is composed of a plurality of gain blocks (GBs) and a fully differential degeneration amplifier (FDDA). The GBs of the DVGA are digitally controlled current mirrors. A common-mode feedback circuitry is used to stabilize the FDDA by providing a stable common-mode voltage. Physical measurements on silicon show that the gain error is merely 0.55 dB given a 70 dB tuning range. This work was supported by National Science Council, Taiwan, under contract nos. NSC96-2628-E-110-019 and NSC96-2920-E-110-001.     

Coil‐Capacitor Circuit Design of a Transcutaneous Energy Transmission System to Deliver Stable Electric Power

A new transcutaneous energy transmission (TET) system was developed for transmitting electrical power to an implanted device, such as an artificial heart in a patient's body. This new design can maintain a stable output voltage independent of the load resistance. The system includes a compensation capacitor to reduce energy loss and increase power transfer efficiency. Experimental results show that the output voltage of the receiving coil changes very little as the load resistance varies from 14.8 Ω to 15 kΩ, which corresponds to a change in output power from 0.1 to 97 W.     

Design and Implementation of a Multimodal Input Device Using a Web Camera

We propose a novel input pointing device called the multimodal mouse (MM) which uses two modalities: face recognition and speech recognition. From an analysis of Microsoft Office workloads, we find that 80% of Microsoft Office Specialist test tasks are compound tasks using both the keyboard and the mouse together. When we use the optical mouse (OM), operation is quick, but it requires a hand exchange delay between the keyboard and the mouse. This takes up a significant amount of the total execution time. The MM operates more slowly than the OM, but it does not consume any hand exchange time. As a result, the MM shows better performance than the OM in many cases.     

Self-aligned inversion n-channel In0.2Ga0.8As/GaAs metal–oxide–semiconductor field-effect-transistors with TiN gate and Ga2O3(Gd2O3) dielectric

A self-aligned process for fabricating inversion n-channel metal–oxide–semiconductor field-effect-transistors (MOSFET’s) of strained In_0.2Ga_0.8As on GaAs using TiN as gate metal and Ga₂O₃(Gd₂O₃) as high κ gate dielectric has been developed. A MOSFET with a 4 μm gate length and a 100 μm gate width exhibits a drain current of 1.5 mA/mm at V_g = 4 V and V_d = 2 V, a low gate leakage of <10^?7 A/cm² at 1 MV/cm, an extrinsic transconductance of 1.7 mS/mm at V_g = 3 V, V_d = 2 V, and an on/off ratio of ～10⁵ in drain current. For comparison, a TiN/Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As MOS diode after rapid thermal annealing (RTA) to high temperatures of 750 °C exhibits excellent electrical and structural performances: a low leakage current density of 10^?8–10^?9 A/cm², well-behaved capacitance–voltage (C–V) characteristics giving a high dielectric constant of ～16 and a low interfacial density of state of ～(2～6) × 10¹¹ cm^?2 eV^?1, and an atomically sharp smooth Ga₂O₃(Gd₂O₃)/In_0.2Ga_0.8As interface.     

Reconfigurable microstrip antenna with polarisation diversity

A single probe-fed reconfigurable microstrip patch antenna with symmetric cross slots is proposed. By controlling four pin diodes on the patch slots, the proposed antenna has right hand circular polarisation, left hand circular polarisation or linear polarisation.     

Evanescent-Coupled Ge p-i-n Photodetectors on Si-Waveguide With SEG-Ge and Comparative Study of Lateral and Vertical p-i-n Configurations

Si-waveguide-integrated lateral Ge p-i-n photodetectors using novel Si/SiGe buffer and two-step Ge-process are demonstrated for the first time. Comparative analysis between lateral Ge p-i-n and vertical p-Si/i-Ge/n-Ge p-i-n is made. Light is evanescently coupled from Si waveguide to the overlaying Ge- detector, achieving high responsivity of 1.16 A/W at 1550 nm with f_{3 dB} bandwidth of 3.4 GHz for lateral Ge p-i-n detector at 5 V reverse bias. In contrast, vertical p-Si/i-Ge/n-Ge p-i-n has lower responsivity of 0.29 A/W but higher bandwidth of 5.5 GHz at -5 V bias. The higher responsivity of lateral p-i-n detectors is attributed to smaller optical mode overlap with highly doped Ge region as in vertical p-i-n configuration.     

Optimization of LDPC codes for modulation and detection in layered multi-antenna architectures

In this paper we first perform the density evolution of LDPC codes in layered multi-antenna architectures using bitinterleaved coded modulation and detection based on successive decoding and interference cancellation. The noise thresholds of LDPC codes are shown to be achieved within 1.2 dB of the capacity for these architectures. We then present a rate allocation method which optimizes the performance of a layered architecture and find good degree distributions for LDPC codes with the rates allocated by our method. Simulation results show that the performance for an optimized layered architecture is better by 4 dB than that for the layered architecture using LDPC codes with the same rate in all layers.     

Facile Fabrication and Superparamagnetism of Silica‐Shielded Magnetite Nanoparticles on Carbon Nitride Nanotubes

Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time.     

Restorable Type Conversion of Carbon Nanotube Transistor Using Pyrolytically Controlled Antioxidizing Photosynthesis Coenzyme

Here, a pyrolytically controlled antioxidizing photosynthesis coenzyme, β‐Nicotinamide adenine dinucleotide, reduced dipotassium salt (NADH) for a stable n‐type dopant for carbon nanotube (CNT) transistors is proposed. A strong electron transfer from NADH, mainly nicotinamide, to CNTs takes place during pyrolysis so that not only the type conversion from p‐type to n‐type is realized with 100% of reproducibility but also the on/off ratio of the transistor is significantly improved by increasing on‐current and/or decreasing off‐current. The device was stable up to a few months with negligible current changes under ambient conditions. The n‐type characteristics were completely recovered to an initial doping level after reheat treatment of the device.