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Now showing items 1 - 16 of 21

  • Novel design techniques for noise-tolerant power-gated CMOS circuits

    Rastogi, Rumi   Pandey, Sujata  

    In this paper we have investigated the single phase sleep signal modulation technique, step-wise V-gs technique and the three-phase reactivation technique to evaluate the noise characteristics of multi-threshold CMOS circuits used in communication systems. The stacking technique is also implemented in this paper for the sleep transistor. The stacking approach helps to minimize leakage power. The mode transition noise minimization techniques have been applied to 32-bit dynamic TSPC adder with stacked sleep transistors in a standard 45-nm CMOS process. The reactivation noise, delay and energy consumption of all the three techniques have been evaluated. It has been shown that the three phase modulation technique significantly minimizes the reactivation delay when the peak noise level is maintained the same for all three techniques. The three phase modulation technique shows 67.3% and 35% reduction in delay compared to the single phase and step-wise V-gs modulation techniques respectively. The reactivation energy is also suppressed by 49.3% and 39.14% with respect to the single-phase and stepwise V-gs techniques.
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  • Modified Sierpenski Antenna With Metamaterial For Wireless Applications

    Aggarwal, Ishita   Pandey, Sujata  

    This paper presents a multiband antenna based on modified sierpenski fractal structure along with metamaterials for wireless applications. Multi bands are obtained at 2.1 GHz, 5.73 GHz, 7.6 GHz and 8.4 GHz with return losses -21.49 dB,-36.36 dB,-45dB, and -23.46 dBrespectively. The dimension of the substrate used for this antenna is 52 x 60 x 1.6 mm(3) and dielectric constant is 4.4 with tan delta of 0.002. The peak gain of 6.6 dB, return loss of -45 dB and VSWR of 1 are obtained at 7.6 GHz. Metamaterial unit cells are loaded on ground to improve the antenna parameters. This is a simple and compact design and has multiband features suitable for WIMAX, WLAN, C-band and X-band applications. This design is simulated by using HFSS 14.
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  • Work function engineered charge plasma diodes for enhanced performance

    Singh, Preeti   Pandey, Sujata  

    Dopingless devices have shown significant improvement over doped devices in terms of doping fluctuations and thermal dependency. In this paper we designed and simulated dopingless/charge plasma diodes where the diode action is implemented by creating a charge plasma under the metal contacts. Two different gate metals or metal silicides are chosen having a work function different from that of the underlying thin silicon body. The gates are separated by a dielectric layer. Several gate combinations are chosen for the diode and performance is evaluated under variation in different process parameters. Good rectifying properties are obtained along with thermal stability of the device. High ON current of 10(-8) A mu m(-1) is obtained for a 20 nm thick device. The simulated results are compared with experimental data and show good agreement.
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  • Effect of Substrate Material on Sensing Behaviour of SAW Based Gas Sensors

    Gupta, Akriti   Kumar, Pradeep   Pandey, Sujata  

    In this paper, we have designed a SAW gas sensor based on MEMS technology to detect volatile organic gases. Finite element analysis of the device had been carried out to observe the changes in the sensor behaviour with the applied gases. Also, the designed SAW Gas Sensor is analysed with different piezoelectric substrate. Lithium Tantalate is found to be best suited for the design which defines the resonant frequency of the device to be approximately 1.184 GHz. The device is further simulated with different volatile organic gases which give corresponding shift in frequency.
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  • Interactions of astrophysical neutrinos with dark matter:a model building perspective

    Pandey, Sujata   Karmakar, Siddhartha   Rakshit, Subhendu  

    We explore the possibility that high energy astrophysical neutrinos can interact with the dark matter on their way to Earth. Keeping in mind that new physics might leave its signature at such energies, we have considered all possible topologies for effective interactions between neutrino and dark matter. Building models, that give rise to a significant flux suppression of astrophysical neutrinos at Earth, is rather difficult. We present a Z-mediated model in this context. Encompassing a large variety of models, a wide range of dark matter masses from 10(-21) eV up to a TeV, this study aims at highlighting the challenges one encounters in such a model building endeavour after satisfying various cosmological constraints, collider search limits and electroweak precision measurements.
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  • A Novel Design of Fractal Antenna:Effect of Different Dielectric Substrate Materials

    Aggarwal, Ishita   Tripathy, Malay Ranjan   Pandey, Sujata  

    In this paper we propose a novel microstrip fractal multiband antenna for RF applications. The antenna is designed on different substrate materials and performance analyzed for return loss, radiation pattern and gain. The substrate material used for antenna design are FR4 and RT-Duriod. Required properties of antenna such as high gain, low return loss, compact and high efficiency can be obtained by selecting the right substrate for the antenna and choosing proper parameters for dielectric constant, values of permeability, permittivity and loss tangent that effect the performance of the antenna.
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  • Interactions of astrophysical neutrinos with dark matter: a model building perspective

    Pandey, Sujata   Karmakar, Siddhartha   Rakshit, Subhendu  

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  • Compact modeling and simulation of nanoscale fully depleted DG-SOI MOSFETS

    Sharma, Rajeev   Pandey, Sujata   Jain, Shail Bala  

    A two dimensional analytical model for nanoscale fully depleted double gate SOI MOSFET is presented. Green's function solution technique is adopted to solve the two dimensional Poisson's equation using Dirichlet's and Neumann's boundary conditions at silicon-silicon di-oxide interface. Based on the derived 2D potential distribution, surface potential distributions in the Si film are analytically obtained. The calculated minimum surface potential is used to develop an analytic threshold voltage model. Simulation is done using ATLAS simulator for a 65 nm device and the results obtained are compared with the proposed 2D model. The model results are found to be in good agreement with the simulated data and other published results.
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  • A dual V-t disturb-free subthreshold SRAM with write-assist and read isolation

    Bhatnagar, Vipul   Kumar, Pradeep   Pandey, Neeta   Pandey, Sujata  

    This paper presents a new dual V-t 8T SRAM cell having single bit-line read and write, in addition to Write Assist and Read Isolation (WARI). Also a faster write back scheme is proposed for the half selected cells. A high V-t device is used for interrupting the supply to one of the inverters for weakening the feedback loop for assisted write. The proposed cell provides an improved read static noise margin (RSNM) due to the bit-line isolation during the read. Static noise margins for data read (RSNM), write (WSNM), read delay, write delay, data retention voltage (DRV), leakage and average powers have been calculated. The proposed cell was found to operate properly at a supply voltage as small as 0.41 V. A new write back scheme has been suggested for half-selected cells, which uses a single NMOS access device and provides reduced delay, pulse timing hardware requirements and power consumption. The proposed new WARI 8T cell shows better performance in terms of easier write, improved read noise margin, reduced leakage power, and less delay as compared to the existing schemes that have been available so far. It was also observed that with proper adjustment of the cell ratio the supply voltage can further be reduced to 0.2 V.
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  • A boosted negative bit-line SRAM with write-assisted cell in 45 nm CMOS technology

    Bhatnagar, Vipul   Kumar, Pradeep   Pandey, Neeta   Pandey, Sujata  

    A new 11 T SRAM cell with write-assist is proposed to improve operation at low supply voltage. In this technique, a negative bit-line voltage is applied to one of the write bit-lines, while a boosted voltage is applied to the other write bit-line where transmission gate access is used in proposed 11 T cell. Supply voltage to one of the inverters is interrupted to weaken the feedback. Improved write feature is attributed to strengthened write access devices and weakened feedback loop of cell at the same time. Amount of boosting required for write performance improvement is also reduced due to feedback weakening, solving the persistent problem of half-selected cells and reliability reduction of access devices with the other suggested boosted and negative bit-line techniques. The proposed design improves write time by 79%, 63% and slower by 52% with respect to LP 10 T, WRE 8 T and 6 T cells respectively. It is found that write margin for the proposed cell is improved by about 4x, 2.4x and 5.37x compared to WRE8 T, LP10 T and 6 T respectively. The proposed cell with boosted negative bit line (BNBL) provides 47%, 31%, and 68.4% improvement in write margin with respect to no write-assist, negative bit line (NBL) and boosted bit line (BBL) write-assist respectively. Also, new sensing circuit with replica bit-line is proposed to give a more precise timing of applying boosted voltages for improved results. All simulations are done on TSMC 45 nm CMOS technology.
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  • Effect of Surface Passivation on the Electrical Characteristics of Nanoscale AlGaN/GaN HEMT

    Gupta, Akriti   Chatterjee, Neel   Kumar, Pradeep   Pandey, Sujata  

    In this paper, we present the effect of passivation layer on the electrical characteristics of AlGaN/GaN HEMT. The energy band diagram, drain current voltage characteristics, transconductance and cut off frequency was calculated for both long channel and short channel devices. It was found that the electrical characteristics of the device improve with the introduction of high K dielectric in the passivation layer. The results obtained agree well with the data available in literature.
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  • Modeling of nanoscale GaNFET in a compact 2-D model with gate stack effects

    Tyagi, Rajesh K.   Ahlawat, Anil   Pandey, Manoj   Pandey, Sujata  

    We report a compact 2D model for AlGaN/GaN HEMT with different gate stack configurations. A two dimensional analysis is done which also includes the various polarization effects. The output characteristics, device transconductance and cut-off frequency (f(T)) for 120nm g ate length device are obtained. Peak transconductance of 320 mS/mm and a cut-off frequency (f(T)) of 120GHz has been obtained. It is also demonstrated that the gate metal pattern largely affect the device characteristics and the small signal parameters. The results show excellent agreement when compared with experimental data thereby proving the validity of the model.
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  • Microwave analysis of a 70 nm InGaAs pHEMT on InP substrate for nanoscale digital IC application

    Ahlawat, Anil   Pandey, Manoj   Pandey, Sujata  

    A new charge-control model for the microwave characteristics of an AlGaAs/lnGaAs/lnP HEMT of 70 nm gate length has been developed. The threshold voltage has been modified by the inclusion of mole fraction and thermal eftects. The current voltage characteristics have been obtained and compared with the 70 nm gate length device. In order to avoid short-channel effects, an aspect ratio (gale length to gate to channel distance) larger than 5 is maintained in the analysis. The small-signal microwave parameters (g(nv), g(d)) have also been evaluated. 2-D analysis has been carried out in the saturation region. The unity gain cut-off frequency of the order of 220 GHz is obtained at a gate length of 70 nm. Device parameters so obtained were used to calculate the hemt Y-parameters. The Y-parameters hold from the threshold region to the edge of saturation. The unilateral gain so obtained from file Y-parameters yield a closer fit to the numerical model. All the results have been compared with the experimental data and show a close agreement and the validity of our model. (C) 2007 Wiley Periodicals, Inc.
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  • An analytical two-dimensional model for AlGaN/GaN HEMT with polarization effects for high power applications

    Tyagi, Rajesh K.   Ahlawat, Anil   Pandey, Manoj   Pandey, Sujata  

    An analytical two-dimensional model for AlGaN/GaN modulation-doped field effect transistor is developed. The spontaneous and piezoelectric polarization effects have been included. Two-dimensional analysis has been carried out in the high field region. The output characteristics, device transconductance and cut off frequency for 120 nm gate length device are obtained. Peak transconductance of 320 mS/mm and a cut off frequency of 120 GHz has been obtained. The results show excellent agreement when compared with experimental data thereby proving the validity of the model. (C) 2007 Elsevier Ltd. All rights reserved.
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  • A compact C-V model for 120 nm AlGaN/GaN HEMT with modified field dependent mobility for high frequency applications

    Gangwani, Parvesh   Pandey, Sujata   Haldar, Subhasis   Gupta, Mridula   Gupta, R. S.  

    We present a theoretical model of AlGaN/GaN high electron mobility transistor (HEMT) that includes the effect of spontaneous and piezoelectric polarization. Present model also incorporates the effect of mole fraction dependent mobility, saturation velocity and the accurate 2-DEG density in HEMT as a function of gate voltage in subthreshold, linear and saturation regimes. This paper reports a detailed 2-D analysis of capacitance-voltage (C-V) characteristics. The contribution of various capacitances including fringing field capacitance on the performance of the device is also shown. The model further predicts the transconductance, drain conductance and frequency of operation and is in close proximity with the experimental data which confirms the validity of proposed model. (C) 2007 Elsevier Ltd. All rights reserved.
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  • Modeling and analysis of fully strained and partially relaxed lattice mismatched AlGaN/GaN HEMT for high temperature applications

    Gangwani, Parvesh   Kaur, Ravneet   Pandey, Sujata   Haldar, Subhasis   Gupta, Mridula   Gupta, R. S.  

    The paper presents an accurate charge control model for a fully strained (FS), and partially relaxed (PR) lattice mismatched AlGaN/GaN HEMT, taking into consideration the effect of spontaneous and piezoelectric polarization. The model also accounts for the mobility degradation with increase in temperature, which is one of the major causes in deterioration of the driving current. By using the variation of band gap with temperature, the temperature dependence on threshold voltage, sheet carrier concentration and drain current is studied. Further, the temperature variation shows the applicability of the device in a variable thermal environment. A close agreement of calculated data with simulated/experimental data proves the validity of the model. (C) 2008 Elsevier Ltd. All rights reserved.
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