The Doherty Power Amplifier With On-Chip Dynamic Bias Control Circuit for Handset Application

A monolithic-microwave integrated-circuit Doherty power amplifier (PA) with an on-chip dynamic bias control circuit for cellular handset application has been designed and implemented. To improve the linearity and efficiency in the operation power ranges, the base and collector biases of the amplifiers, except the drive amplifier of the main path, are controlled according to the average output power. The base biases are controlled using the on-chip circuit and collector biases by the dc/dc chip to reduce the average dc consumption power. The power-added efficiency (PAE) is improved approximately 6% by the base dynamic bias control, and approximately 14% by the collector/base dynamic control from the class AB at Pout=16 dBm, respectively. If the dc/dc converter efficiency is 100%, the PAE could be improved approximately 17.5% from class AB, reaching to 29.2% at Pout=16 dBm. In the intermediate power level from 22 to 28 dBm, the PAE is over 34.3%. The average current consumption of the PA with the dynamic bias control is 22.5 mA in urban and 37.3 mA in suburban code-division multiple-access environments, which are reduced by 36%-46.7%, compared to the normal operation. The adjacent channel power ratio is below 47.5 dBc, and the PAE at the maximum power is approximately 43.3% in the dynamic bias operations     

Highly linear and low noise 2.4 GHz RF front-end circuits using transformer and vertical NPN BJT

The proposed RF front-end circuits consist of a low noise amplifier using an on-chip transformer and a downconversion mixer using a parasitic vertical bipolar junction transistor and have been implemented in 0.18 mum deep n-well CMOS process. A gain of 33 dB, an IIP3 of -12 dBm, and a DSB noise figure of 4.5 dB have been achieved while consuming 5 mW from a 1.8 V supply     

Thermal Investigation of GaN-Based Laser Diode Package

We investigated thermal behavior of GaN-based laser diode (LD) packages as a function of cooling systems, die attaching materials, chip loading conditions, and optical performances. The electrical thermal transient technique was employed for the thermal measurement of junction temperature and thermal resistance of LD packages. The results demonstrate that the total thermal resistance of LD packages is controlled mainly by the packaging design rather than the chip structure itself. Significant changes in thermal resistance with input current were observed under a natural cooling system because of the sensitive change in the heat transfer coefficient with the change in temperature. Employment of PbSn as a die attachment was more advantageous over the Ag-paste in the thermal behavior of LD packages. The LD package with epi-down structure resulted in the lower thermal resistance compared to one with epi-up structure. A continuous increase in junction temperature was measured after lasing. It was attributed to an increase in the thermal resistance of LD when it took the optical power into an account. Effective input power was decreased by the lasing and led to high thermal resistance values.     

Photonic Technologies for Quantum Information Processing

The last several years have seen tremendous progress toward practical optical quantum information processing, including the development of single- and entangled-photon sources and high-efficiency photon counting detectors, covering a range of wavelengths. We review some of the recent progress in the development of these photonic technologies. PACS: 03.67.-a, 42.50.Dv, 42.65.Lm, 78.67.Hc, 85.60.Gz     

Acoustic monitoring of HV equipment with optical fiber sensors

This paper presents the preliminary results on the application of optical fiber sensor (OFS) for the measurements of discharging signals in insulating oil. An all-optical-fiber-sensing system using a Mach-Zehnder interferometry technique was constructed. It was found that the pressure wave produced by discharges at the needle-sphere electrodes could be detected by OFS, which was compared with signals from a current probe and PZT sensor. By comparing amplitudes of acoustic signal measured by OFS, a correlation between acoustic and electrical discharge signals was observed.     

The effect of an atmospheric pressure plasma treated MgO layer on the discharge performance of an AC plasma display panel

The effect of an atmospheric pressure plasma treated MgO layer on the discharge performance of an alternating current plasma display panel (AC PDP) was investigated by measuring the contact angle, the surface roughness, the composition, the breakdown and sustaining voltages. The plasma cleaning was performed using the He/O₂/Ar gas mixture. Higher contact angle (35°) of water droplet on the MgO surface and the MgO surface roughness (90 nm, R_max) after one day duration in the air was significantly reduced to 4° and 54 nm (R_max) after the plasma cleaning. After the plasma treatment, the adsorbed CO₂, CO, H₂O impurities on the MgO surface are effectively removed. The breakdown and sustaining voltages were reduced probably due to the increase of secondary electron emission coefficient of MgO, implying that the plasma cleaning process of the MgO layer is beneficial for the improvement of the discharge performance of the AC PDPs.     

Microstructure of electroplated hard chromium coatings after plasma nitrocarburizing

Plasma nitrocarburizing was carried out on the hard chromium coating deposited on SM45C mild carbon steel substrate by electroplating. After plasma nitrocarburizing at 720 °C for 20 h, a 6–7-μm-thick nitride layer consisting of CrN and Cr₂N was formed on the surface of Cr coating with the microhardness of about 950–1100 HV0.1. Due to the effect of annealing caused by plasma nitrocarburizing process at higher temperature and the Cr being a strong carbide-forming element, the carbon in steel substrate diffused outward into the Cr coating and reacted with Cr forming Cr carbide interface layer between the Cr electroplating and substrate. The nitrogen going into the microcracks and the volume increase accompanied by Cr nitride and carbide formation would cause the microcracks inherent to hard chromium plating disappear and improve its corrosion resistance. The microstructures of nitride and carbide layers were studied using X-ray diffraction and cross-sectional transmission electron microscopy.     

Hydrolysis of wheat starch and its effect on the Falling Number procedure: experimental observations†

The underlying mechanisms of starch hydrolysis in cereal grains, as measured by the Falling Number procedure, were studied. Wheat starch, spiked with barley malt α‐amylase, was used as a model experimental system. A non‐invasive and real‐time monitoring system was developed to simultaneously record the sample temperature and stirrer velocity profiles, which are critical parameters that affect Falling Number readings. Experimental results show that the repeatability of the Falling Number procedure can be improved by slowing the heating rate, which is accomplished by increasing the quantity of sample components (ie starch and water) while maintaining the same proportion as currently specified in standard methodology. Among the tested range of heating rates, the best repeatability of Falling Number readings was obtained with 8.4 g starch and 30.0 g water. The experimental findings of this study also serve as basic information for the development of mathematical models on the hydrolysis of starch. © 1999 Society of Chemical Industry     

Synthesis of block copolymers having perfluoroalkyl and silicone‐containing side chains using diazo macroinitiator and their surface properties

The fluorosilicone block copolymers of poly(perfluoroalkylethyl acrylate)‐b‐poly(3‐[tris(trimethylsilyloxy)silyl] propyl methacrylates) (PFA‐b‐PSiMAs) having perfluoroalkyl and silicone‐containing side chains were obtained by three‐step synthetic approaches. In the first step, hydroxyl‐terminated poly(perfluoroalkylethyl acrylate) macromonomer (PFAM) was prepared by the free‐radical polymerization of perfluoroalkylethyl acrylate and 2‐mercaptoethanol. In the second step, PFAM initiator (PFAMI) was prepared from the condensation reaction of the hydroxyl‐terminated PFAM and 4,4′‐azobis‐4‐cyanopentanoic acid chloride (ACPC). ACPC was obtained from the reaction of 4,4′‐azobis‐4‐cyanopentanoic acid and phosphorus pentachloride. In the third step, PFA‐b‐PSiMAs (BPFSs) were synthesized from the reaction of PFAMI macroinimer and SiMA. Fourier transform infrared spectroscopy and ¹H‐NMR analyses verified that the syntheses of ACPC, hydroxyl‐terminated PFAM, PFAMI, and BPFS were completed successfully. The intrinsic surface energies of BPFSs and their surface modification effects on poly(vinyl chloride) film were investigated by analyzing the surface free energies and atomic compositions of the outermost layer of the surfaces. BPFSs exhibit extremely low surface free energies of about 9.7–13.0 dynes/cm. It was confirmed that BPFS, having extremely low surface free energy, is preferentially enriched at the outermost layer of the surface of BPFS/poly(vinyl chloride) blend. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1917–1926, 1999     

Pervaporation separation of water–isopropanol mixture using carboxymethylated poly(vinyl alcohol) composite membranes

The pervaporation separation of water–isopropanol mixtures was carried out using carboxymethylated poly(vinyl alcohol) (CMPVA) composite membranes. Carboxymethylated PVA (CMPVA) was synthesized by reacting PVA with various concentrations of monochloroacetic acid. Substitution efficiency of the CMPVA ranged from 12–32%. The cross‐sectional structure of the composite membrane for pervaporation was confirmed by scanning electron microscopy (SEM) exhibiting a 20‐μm active skin layer. Glass transition temperature of the CMPVA was in the range of 74–84°C, and decreased with increasing substitution efficiency. Degree of swelling and permeation flux for water–isopropanol in pervaporation increased with the substitution degree of carboxymethylation. CMPVA composite membrane, having 16% substitution efficiency, showed the following pervaporation performance; permeation flux of 831 g/m² h and separation factor of 362 measured at 80°C and 85 wt % feed isopropanol concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 241–249, 1999