Gate leakage current reduction in IP3 SRAM cells at 45 nm CMOS technology for multimedia applications

We have presented an analysis of the gate leakage current of the IP3 static random access memory (SRAM) cell structure when the cell is in idle mode (performs no data read/write operations) and active mode (performs data read/write operations), along with the requirements for the overall standby leakage power, active write and read powers. A comparison has been drawn with existing SRAM cell structures, the conventional 6T, PP, P4 and P3 cells. At the supply voltage, V_DD = 0.8 V, a reduction of 98%, 99%, 92% and 94% is observed in the gate leakage current in comparison with the 6T, PP, P4 and P3 SRAM cells, respectively, while at V_DD = 0.7 V, it is 97%, 98%, 87% and 84%. A significant reduction is also observed in the overall standby leakage power by 56%, the active write power by 44% and the active read power by 99%, compared with the conventional 6T SRAM cell at V_DD = 0.8 V, with no loss in cell stability and performance with a small area penalty. The simulation environment used for this work is 45 nm deep sub-micron complementary metal oxide semiconductor (CMOS) technology, t_ox = 2.4 nm, V_thn = 0.22 V, V_thp = 0.224 V, V_DD = 0.7 V and 0.8 V, at T = 300 K.     

Effect of voltage sweep direction on the performance evaluation of P3HT : PCBM solar cells

Investigations on the effect of direction of voltage sweeps, on the current density–voltage (J–V) characteristics in polymer bulk‐heterojunction solar cells, based on the blend of poly(3‐hexylthiophene) (P3HT) and phenyl [6,6] C₆₁ butyric acid methyl ester (PCBM), are reported with time. On the freshly prepared device, the direction of the voltage sweep did not have any effect; however, as the device started degrading, the change in direction of the voltage sweep resulted into different characteristics. Analysis beyond complete degradation, when all the photovoltaic parameters reduced to zero, revealed some interesting results. The J–V characteristics, measured with voltage sweep from −ve to +ve voltage, both in the dark and under illumination, were observed to pass through the second quadrant. On the other hand, with the change in the direction of voltage sweep, viz. from +ve to −ve voltage, the characteristics both in the dark and under illumination passed through the fourth quadrant. These results have been explained on the basis of polarization of the degraded active layer due to applied external voltage. This is an important effect and is observed to depend on the applied voltages during performance evaluation and becomes more prominent with time. This effect puts a question mark on the correctness of the method for calculation of the parameters of a degraded device. Studies on degradation of P3HT : PCBM solar cells showed that both the short circuit current density (J_sc) and the power conversion efficiency (η) decay exponentially, whereas the open circuit voltage (V_oc) decays almost linearly with time. Copyright © 2012 John Wiley & Sons, Ltd.     

Shorting pin loaded dual-band compact rectangular microstrip antenna

Theoretical and experimental investigations carried out on shorted microstrip patch antenna for dual band operation. The investigations were carried out by varying the shorting-pin position from the edge to the centre of the patch; such an antenna provides a frequency tunability range from 0.88?GHz to 1.08?GHz for first resonance and from 2.20?GHz to 2.59?GHz for second resonance. A frequency ratio of about 2.91 to 2.2 for the two operating frequencies is observed. When the shorting-pin position is close to centre or at the centre of the patch, a single resonant frequency is observed. It is also observed that the resonant frequency of the antenna heavily depends upon the thickness of the substrate, dielectric constant of the substrate and radius of the shorting-pin.     

Fast complex memory polynomial-based adaptive digital predistorter

Today's 3G wireless systems require both high linearity and high power amplifier (PA) efficiency. The high peak-to-average ratios of the digital modulation schemes used in 3G wireless systems require that the RF PA maintain high linearity over a large range while maintaining this high efficiency; these two requirements are often at odds with each other with many of the traditional amplifier architectures. In this article, a fast and easy-to-implement adaptive digital predistorter has been presented for Wideband Code Division Multiplexed signals using complex memory polynomial work function. The proposed algorithm has been implemented to test a Motorola LDMOSFET PA. The proposed technique also takes care of the memory effects of the PA, which have been ignored in many proposed techniques in the literature. The results show that the new complex memory polynomial-based adaptive digital predistorter has better linearisation performance than conventional predistortion techniques.     

Time delays and angles of arrival estimation using known signals

Channel estimation in a multipath mobile communication system is addressed in this paper, and a novel approach based on the linear prediction in frequency domain and the singular value decomposition technique is presented for joint estimation of the angles of arrival and the time delays of multiple reflections of a known signal. Simulation results illustrating the performance of the proposed algorithm are included, and the results show that the proposed method is close in accuracy when compared to the iterative maximum-likelihood method. However, when the two methods are compared in computational complexity, it is demonstrated that the proposed method reduces the complexity to nearly half of that of the maximum-likelihood method. The Cramer–Rao bounds are computed for comparison.     

Mie‐Resonant Membrane Huygens' Metasurfaces

All‐dielectric metasurfaces have become a new paradigm for flat optics as they allow flexible engineering of the electromagnetic space of propagating waves. Such metasurfaces are usually composed of individual subwavelength elements embedded into a host medium or placed on a substrate, which often diminishes the quality of the resonances. The substrate imposes limitations on the metasurface functionalities, especially for infrared and terahertz frequencies. Here a novel concept of membrane Huygens' metasurfaces is introduced. The metasurfaces feature an inverted design, and they consist of arrays of holes made in a thin membrane of high‐index dielectric material, with the response governed by the electric and magnetic Mie resonances excited within dielectric domains of the membrane. Highly efficient transmission combined with the 2π phase coverage in the freestanding membranes is demonstrated. Several functional metadevices for wavefront control are designed, including beam deflector, a lens, and an axicon. Such membrane metasurfaces provide novel opportunities for efficient large‐area metadevices, whose advanced functionality is defined by structuring rather than by chemical composition.     

Long‐Range,Entangled Carbon Nanotube Networks in Polycarbonate

A method is presented for dispersing ropes or bundles of single‐walled carbon nanotubes (RCNTs) in a polycarbonate (PC) matrix. Films of PC/RCNT composites are produced, with thicknesses ranging from 10 to 60 μm, and containing small concentrations (0.06–0.25 wt.‐%) of RCNT. Our process is based on a unique method of hot casting, annealing, and drying from dichlorobenzene solution. A wet annealing prior to complete drying yields a uniform and transparent film. Despite the low RCNT loading, scanning electron microscopy (SEM) analysis of the films after fracture reveals that the RCNTs form an entangled network throughout the film, which is a key requirement for enhanced properties. An increase of up to 30 % in the Young's modulus, as compared to PC, results with this method of composite fabrication.     

Analysis of Rake reception with multiple symbol weight estimation for antipodal signaling

Consider a Rake receiver for coherent binary antipodal signaling with: 1) a delayed received signal configuration; 2) weight estimation by matched filtering using the reference signal along with the decisions of the previous M symbol intervals; and 3) predetection maximal-ratio combining (MRC). The weight estimation errors here are not independent of the additive noise, and do not fit into the Gaussian weighting error model for MRC. Here we analyze the error performance of the receiver by obtaining the conditional symbol error probability, conditioned on past decisions, from the characteristic function of the decision variable, and getting the unconditional error probability (UEP) for a block of M consecutive symbols using a Markov model of the decision process. The channel is Rayleigh fading with independent and identically distributed branch gains. Results show that the error performance of the Gaussian distributed weighting error model is a bound for that of multiple symbol weight estimation by matched filtering, and the steady state UEP decreases with increase of M, but the amount of decrease reduces as M increases.     

Processing of Ta2O5 powders for electronic applications

The particle size, surface area, morphology, and purity of tantalum pentoxide are critical for some of its applications in the manufacture of several, electronic products. Although the purity of different grades of Ta₂O₅, such as standard technical grade, carbide grade, and optical grade, have been well documented, there is no report on the morphology and other surface characteristics of Ta₂O₅ powders. The objective of this paper is to review various methods and recent developments in the processing of tantalum oxide powders. The other objective of this paper is to report on the morphology, particle size, and surface area of tantalum oxide obtained from different methods of preparation. The work reported in this paper will be useful for researchers involved in the development of tantalum-related electronic materials.