Improved HBT linearity with a "post-distortion"-type collector linearizer

An HBT amplifier with a "post-distortion"-type linearizer utilizing a base-collector junction diode shows more than 8-dB improvement of adjacent channel power ratio, and the collector linearizer comprising a reverse biased base-collector junction diode requires no additional dc power consumption and has no deterioration of RF performance. The linearization technique of post-distortion compensates the nonlinearity of HBTs, which arises from the C/sub bc/ variation due to a large-signal swing.     

Tunable multiwavelength fiber laser employing a comb filter based on a polarization-diversity loop configuration

A tunable multiwavelength fiber laser based on a semiconductor optical amplifier (SOA) is newly proposed. The proposed fiber laser employs a fiber comb filter based on a polarization-diversity loop configuration (PDLC) for the multiwavelength selection. The spectral characteristic of the comb filter is graphically explained by tracing the state of polarization (SOP) of the light propagating through the filter on the Poincare sphere. Particularly, the method of adjusting the filter characteristics is established with the help of the Poincare-sphere representation. The experimental results show that 18 laser lines oscillate with the signal to amplified spontaneous emission noise ratio over 25 dB. Particularly, all of the laser lines with a fixed channel spacing of /spl sim/ 0.8 nm can be continuously shifted by adjusting only a wave plate contained within the filter.     

Excellent Switching Uniformity of Cu-Doped $hbox{MoO}_{x}/hbox{GdO}_{x}$ Bilayer for Nonvolatile Memory Applications

We have investigated a Cu-doped MoO_x/GdO_x bilayer film for nonvolatile memory applications. By adopting an ultrathin GdO_x layer, we obtained excellent device characteristics such as resistance ratio of three orders of magnitude, uniform distribution of set and reset voltages, switching endurance up to 10⁴ cycles, and ten years of data retention at 85degC. By adopting bilayer films of Cu-doped MoO_x/GdO_x, a local filament was formed by a two-step process. Improved memory characteristics can be explained by the formation of nanoscale local filament in the ultrathin GdO_x layer.     

Single-Chip Eye Tracker Using Smart CMOS Image Sensor Pixels

The eye tracker is a system that detects the point where the user gazes on. The conventional eye tracker using a Charge-Coupled Device (CCD) camera needs many peripherals and software computation causing high cost, computation time and power consumption. This paper proposes a single-chip eye tracker using smart CMOS Image Sensor (CIS) pixels. The proposed eye tracker does not require additional peripherals and operates at higher speed than the conventional approach. The prototype chip was designed and fabricated for a 32 × 32 smart CIS pixels array with a 0.35-μ m CMOS process. The test results show ± 1 pixel error at the rate of 125 frame-per-second. The power consumption is 260 mW with 3.3 V supply voltage and the silicon area is 3.8 mm²     

Photocurable propyl-cinnamate-functionalized polyhedral oligomeric silsesquioxane as a gate dielectric for organic thin film transistors

A polyhedral oligomeric silsesquioxane (POSS)-based insulating material with photocurable propyl-cinnamate groups (POSS-CYNNAM) was designed and synthesized through simple single step reaction for use as a gate dielectric in organic thin-film transistors (OTFT). POSS-CYNNAM was soluble in common organic solvents and formed a smooth thin film after spin-casting. A thin film of POSS-CYNNAM was cross-linked and completely solidified under UV irradiation without the use of additives such as photoacid generators or photoradical initiators. ITO/insulator/Au devices were fabricated and characterized to measure the dielectric properties of POSS-CYNNAM thin films, such as leakage current and capacitance. A pentacene-based OTFT using the synthesized insulator as the gate dielectric layer was fabricated on the transparent indium tin oxide (ITO) electrode, and its performance was compared to OTFTs using thermally cross-linked poly(vinyl phenol) (PVP) as the insulator. The fabricated POSS-CYNNAM OTFT showed a comparable performance to devices based on the PVP insulator with 0.1 cm²/Vs of the field effect mobility and 4.2 × 10⁵ of an on/off ratio.     

Design and practical implementation of multifrequency RF front ends using direct RF sampling

The use of direct RF sampling has been explored as a means of designing multifrequency RF front ends. Such front ends will be useful to multifrequency RF applications such as global navigation satellite system receivers that use global positioning system (GPS) L1, L2, and L5 signals and Galileo signals. The design of a practical multifrequency direct RF sampling front end is dependent on having an analog-to-digital converter whose input bandwidth accommodates the highest carrier frequency and whose maximum sampling frequency is more than twice the cumulative bandwidth about the multiple carrier signals. The principle of direct RF sampling is used to alias all frequency bands of interest onto portions of the Nyquist bandwidth that do not overlap. This paper presents a new algorithm that finds the minimum sampling frequency that avoids overlap. This design approach requires a multifrequency bandpass filter for the frequency bands of interest. A prototype front end has been designed, built, and tested. It receives a GPS coarse/acquisition code at the L1 frequency and GPS antispoofing precision code at both L1 and L2. Dual-frequency signals with received carrier-to-noise ratios in excess of 52 dB-Hz have been acquired and tracked using this system.     

Carrier Lifetime Measurements in Long-Wave Infrared InAs/GaSb Superlattices Under Low Excitation Conditions

Minority carrier lifetime in long-wave infrared (LWIR) type?II InAs/GaSb superlattices was studied using the optical modulation response (OMR) technique in wide ranges of excitation and temperature. The measured carrier lifetime was found to increase superexponentially with decreasing excitation power density below the level of 1?mW/cm² to 2?mW/cm². The phenomenon was qualitatively explained by the presence of shallow trapping centers.     

Functionality of Dual‐Phase Lithium Storage in a Porous Carbon Host for Lithium‐Metal Anode

Lithium (Li) metal is regarded as the most attractive anode material for high‐energy Li batteries, but it faces unavoidable challenges—uncontrollable dendritic growth of Li and severe volume changes during Li plating and stripping. Herein, a porous carbon framework (PCF) derived from a metal–organic framework (MOF) is proposed as a dual‐phase Li storage material that enables efficient and reversible Li storage via lithiation and metallization processes. Li is electrochemically stored in the PCF upon charging to 0 V versus Li/Li⁺ (lithiation), making the PCF surface more lithiophilic, and then the formation of metallic Li phase can be induced spontaneously in the internal nanopores during further charging below 0 V versus Li/Li⁺ (metallization). Based on thermodynamic calculations and experimental studies, it is shown that atomically dispersed zinc plays an important role in facilitating Li plating and that the reversibility of Li storage is significantly improved by controlled nanostructural engineering of 3D porous nanoarchitectures to promote the uniform formation of Li. Moreover, the MOF‐derived PCF does not suffer from macroscopic volume changes during cycling. This work demonstrates that the nanostructural engineering of porous carbon structures combined with lithiophilic element coordination would be an effective approach for realizing high‐capacity, reversible Li‐metal anodes.