A low-power and high-gain fully integrated CMOS LNA

In this paper, we present the design of a fully integrated CMOS low noise amplifier (LNA) with on-chip spiral inductors in 0.18 μm CMOS technology for 2.4 GHz frequency range. Using cascode configuration, lower power consumption with higher voltage and power gain are achieved. In this configuration, we managed to have a good trade off among low noise, high gain, and stability. Using common-gate (CG) configuration, we reduced the parasitic effects of C_gd and therefore alleviated the stability and linearity of the amplifier. This configuration provides more reverse isolation that is also important in LNA design. The LNA presented here offers a good noise performance. Complete simulation analysis of the circuit results in center frequency of 2.4 GHz, with 37.6 dB voltage gain, 2.3 dB noise figure (NF), 50 Ω input impedance, 450 MHz 3 dB power bandwidth, 11.2 dB power gain (S₂₁), high reverse isolation (S₁₂)<−60 dB, while dissipating 2.7 mW at 1.8 V power supply.     

Co-channel Interference Assessment for Line-of-Sight and Nearly Line-of-Sight Millimeter-Waves Cellular LMDS Architecture

Behavior of co-channel interference in fixed wireless cellular systems, such as millimeter-waves Local Multipoint Distribution Service (LMDS), is different compared to what has been established for mobile microwave systems. This is due to utilization of a high-gain antenna for the subscriber. In this paper, first the analysis of signal-to-interference ratio (SIR) is presented for line-of-sight and nearly line-of-sight LMDS architecture. In this analysis, the effects of precipitation and foliage attenuation and depolarization have been considered. These two parameters have negligible effect on the microwave mobile systems but in millimeter-wave range are among the most important factors in the link budget. To mitigate the fading due to shadowing by buildings and trees, a highly overlapped architecture and macro-diversity are proposed. After analysis of downlink SIR in previously proposed cellular systems, a cellular architecture is proposed based on polarization interleaving and frequency segmentation which has a much higher SIR yield. The statistical assessment of SIR is accomplished by assuming lognormal distribution for the received signals.     

Low power and high gain current reuse LNA with modified input matching and inter-stage inductors

In this paper we present a fully integrated current reuse CMOS LNA (low noise amplifier) with modified input matching circuitry and inductive inter-stage architecture in 0.18 μm CMOS technology. To reduce the large spiral inductors that actually require larger surface area for their fabrication, two parallel LC circuits are used with two small spiral on-chip inductors. Using cascode configuration equipped by parallel inter-stage LCs, we achieved lower power consumption with higher power gain. In this configuration we used two cascoded transistors to have a good output swing suitable for low voltage technology compared to other current reuse configurations. This configuration provides better input matching, lower noise figure and more reverse isolation which is vital in LNA design. Complete analytical simulation of the circuit results in center frequency of 5.5 GHz, with 1.9 dB NF, 50 Ω input impedance, 1 GHz 3 dB power bandwidth, 20.5 dB power gain (S₂₁), high reverse isolation (S₁₂)<−48 dB, −18.5 dB input matching (S₁₁) and −21.3 dB output matching (S₂₂), while dissipating as low power as 2 mW at 1.8 V power supply.     

Low‐Cost Chitosan‐Derived N‐Doped Carbons Boost Electrocatalytic Activity of Multiwall Carbon Nanotubes

An effective strategy is proposed to enhance the oxygen reduction reaction (ORR) performance of multiwall carbon nanotubes (MWCNTs) in both acid and alkaline electrolytes by coating them with a layer of biomass derivative N‐doped hydrothermal carbons. The N‐doped amorphous carbon coating plays triple roles: it (i) promotes the assembly of MWCNTs into a 3D network therefore improving the mass transfer and thus increasing the catalytic activity; (ii) protects the Fe‐containing active sites, present on the surface of the MWCNTs, from H₂O₂ poisoning; (iii) creates nitrogenated active sites and hence further enhances ORR activity and robustness.     

Development of Graphene Oxide/Polyaniline Inks for High Performance Flexible Microsupercapacitors via Extrusion Printing

Extrusion printing of interdigitated electrodes for flexible microsupercapacitors (fMSCs) offers an attractive route to the fabrication of flexible devices where cost, scalability, and processability of ink formulations are critical. In this work, highly concentrated, viscous, and water‐dispersible inks are developed based on graphene oxide (GO)/polyaniline (PANi) composite for extrusion printing. The optimized GO/PANi‐based all‐solid‐state symmetric fMSCs obtained by extrusion printing interdigitated microelectrodes can deliver outstanding areal capacitance of 153.6 mF cm^?2 and volumetric capacitance of 19.2 F cm^?3 at 5 mV s^?1. It is shown that by fabricating asymmetric fMSCs using the GO/PANi as positive electrode and a graphene‐based negative electrode, the voltage window can be widened from 0.8 to 1.2 V and improvements can be achieved in energy density (from 3.36 to 4.83 mWh cm^?3), power density (from 9.82 to 25.3 W cm^?3), and cycling stability (from 75% to 100% capacitance retention over 5000 cycles) compared with the symmetric counterpart. The simple ink preparation and facile device fabrication protocols reported here make the scalable fabrication of extrusion printed fMSCs a promising technology.     

Quantitative Comparison Between Dislocation Densities in Offcut 4H-SiC Wafers Measured Using Synchrotron X-ray Topography and Molten KOH Etching

Molten KOH etching and x-ray topography have been well established as two of the major characterization techniques used for observing as well as analyzing the various crystallographic defects in both substrates and homoepitaxial layers of silicon carbide. Regarding assessment of dislocation density in commercial wafers, though the two techniques show good consistency in threading dislocation density analysis, significant discrepancy is found in the case of basal plane dislocations (BPDs). In this paper we compare measurements of BPD densities in 4-inch 4H-SiC commercial wafers assessed using both etching and topography methods. The ratio of the BPD density calculated from topographic images to that from etch pits is estimated to be larger than 1/sinθ, where θ is the offcut angle of the wafer. Based on the orientations of the defects in the wafers, a theoretical model is put forward to explain this disparity and two main sources of errors in assessing the BPD density using chemical etching are discussed.     

Performance evaluation of multihop ad hoc WLANs

Ongoing technological advances in portable devices, coupled with the need for continuous connectivity while mobile, have made ad hoc networks a compelling research and development topic, particularly in a challenging multimedia multihop scenario. The ability of IEEE 802.11's ad hoc mode of operation, as a dominating wireless local area network (WLAN) protocol, to serve multihop networks requires thorough investigation. In this article, through considering crucial real-life physical phenomena and avoiding as many confining assumptions as possible, system performance measures such as delay and packet failure rate are evaluated. As a result, the importance of adequate selection of the system parameters toward performance improvement is underscored. Moreover, the simulation results imply that by complementing through priority provisions, coordination, route reservation, clustering, and optimum channel coding considerations, the IEEE 802.11 medium access control (MAC) protocol can survive in a multihop scenario. The custom simulation environment developed features modularity, comprising traffic generator, mobility, wireless channel, and IEEE 802.11 protocol modules, and is capable of accommodating many more of the physical phenomena involved.     

On the code and interleaver design of broadband OFDM systems

In this letter, we study the performance of space-frequency-coded orthogonal frequency-division modulation systems over multiple-input multiple-output frequency-selective channels. The diversity and coding advantages are derived in terms of the minimum Hamming distance and the minimum squared product distance of the code as well as the relative frequency locations (tones) where a pair of codewords with the minimum Hamming distance differ. These relationships between performance and well-defined code parameters provide new insight to code construction and interleaving design. In addition, we propose a block interleaver that yields nearly optimal coding advantage for space-frequency trellis codes.     

Digital versatile disc bipolar electrode: A fast and low-cost approach for visual sensing of analytes and electrocatalysts screening

This work represents a new, extremely low cost and easy method for fabrication of bipolar electrode (BPE) for rapid and simultaneous screening of potential candidates for electrocatalytic reactions and sensing applications. Our method takes advantage of the silver reflective layer deposited on already available recordable digital versatile disc (DVD-R) polycarbonate substrate which acts as BPE. Oxidation of the reflective layer of the DVD-R in anodic pole of the BPE results in a permanent and visually measurable dissolute length. Therefore, one could correlate the electrocatalytic activity of the catalyst at the cathodic pole of the BPE, as well as the concentration of analyte in the solution, to the dissolution length of the BPE. To illustrate the promising applications of this new substrate as BPE, p-benzoquinone (BQ) and hydrogen peroxide were tested as model targets for the sensing application. Moreover, in order to show the feasibility of using DVD BPEs for screening applications, the electrocatalytic activity of Pt, Pd, Au, and pristine DVD substrate toward hydrogen evolution reaction (HER) were compared using an array of BPEs prepared on DVD substrate.