Papers by Gholamreza Karimi
IEEE Transactions on Circuits and Systems I: Regular Papers, 2014
IEEE Access
Neuromorphic architectures are systems that aim at using the principles of biological neural func... more Neuromorphic architectures are systems that aim at using the principles of biological neural functions as their basis of operation. One of the most significant challenges in neuromorphic studies, which play an important role in information processing, is the investigation of astrocytes in neuronal models. This paper presents an efficient FPGA-based digital implementation of a spiking neuron model, known as the 2D Hindmarsh-Rose model, and neuron-astrocyte model. To avoid costly computations, the astrocyte and 2D Hindmarsh-Rose models were approximated. The approximation was performed based on multiple method such as the piecewise linear model (PWL) and the particle swarm optimization (PSO) method. As known, noisy mechanisms are stochastic processes which help to improve information processing in nonlinear dynamical systems, including neural systems, and results in more realistic behaviors. Therefore, we presented the noise implications for the approximated neuron-astrocyte models. By introducing two networks consisting of ten 2D Hindmarsh-Rose neurons, the role of the approximated astrocyte in regulation of the neural activities and noise tolerance of the neural networks was investigated. Accordingly, the feasibility of the digital implementation for the proposed 2D Hindmarsh-Rose neuron and the neuron-astrocyte models was studied. Experimental findings of the hardware synthesis and physical implementation on a fieldprogrammable gate array (FPGA) were expounded for the modified spiking neuron model and the approximated astrocyte models with maximum clock frequencies of 247.35 MHz and 279.28 MHz, respectively, showed an increase by about 3.5 times in the frequency in both approximated models. The number of slice registers decreased by 22% and 20% in the proposed 2D Hindmarsh-Rose and astrocyte models, respectively. Also, the networks in the original and approximated 2D Hindmarsh-Rose neurons and astrocyte were synthesized on an FPGA platform. Maximum clock frequencies for both networks were 73.09 MHz and 182.18 MHz, respectively. Comparison of the synthesis results of the two networks showed decreases by 58% and 98% in the number of slice registers and the number of DSPs, respectively. INDEX TERMS Field-programmable gate array, Hindmarsh-Rose neuron model, neuromorphic architectures, spiking neuron model, noisy astrocyte, multiplierless implementation This article has been accepted for publication in IEEE Access.
2010 5th IEEE Conference on Industrial Electronics and Applications, 2010
... R. Karimi Electrical Engineering Department of Razi University Kermanshah, Iran ghkarimi@razi... more ... R. Karimi Electrical Engineering Department of Razi University Kermanshah, Iran [email protected] ... B. Input Matching Most RF instruments and coaxial cables have standardized impedances of Ω 50 , thus the input stage of the amplifier is required to match to Ω 50 to have ...
2006 IEEE International Multitopic Conference, 2006
ETRI Journal, 2015
A novel microstrip low-pass filter is presented to achieve an ultra-wide stopband with 11 harmoni... more A novel microstrip low-pass filter is presented to achieve an ultra-wide stopband with 11 harmonic suppression and very sharp skirt characteristics. The filter is composed of a modified U-shaped resonator (which creates two fully adjustable transmission zeroes), a T-shaped resonator (which determines a cutoff frequency), and four radial stubs (which provide a wider stopband). The operating mechanism of the filter is investigated based on a proposed equivalent-circuit model, and the role of each section of the proposed filter in creating null points is theoretically discussed in detail. The presented filter with 3 dB cutoff frequency (f c = 2.35 GHz) has been fabricated and measured. Results show that a relative stopband bandwidth of 164% (referred to as a 22 dB suppression) is obtained while achieving a high figure-of-merit of 15,221.
AEU - International Journal of Electronics and Communications, 2015
ABSTRACT
International Journal of Microwave and Wireless Technologies, 2014
In this paper, a novel compact ultra-wideband (UWB) bandpass filter (BPF) without and with one sh... more In this paper, a novel compact ultra-wideband (UWB) bandpass filter (BPF) without and with one sharply notched band is presented. The UWB bandpass characteristic is achieved using slotted resonators (SR) and a notch is obtained by spiral defected ground structure (SDGS) without any change in SR structure. Center frequency of the notched band can be easily changed (from 5 to 9 GHz) by tuning the dimensions of SDGS. To verify the feasibility of the proposed filter, two UWB BPFs, one without the notched band and the other with a notched band, at 8.0 GHz are developed and fabricated, there by suppressing the spurious satellite-communication signal within passband. Measured results of two fabricated filters have the advantages of wide −3 dB bandwidth from 3.1 to 10.6 GHz (which satisfies the requirements of US Federal Communication Commission -specified UWB limits), compact size, low insertion loss (<0.6 dB), and a wide upper stopband with high attenuation (−20 to −50 dB).
Wireless Personal Communications, 2014
ABSTRACT Aiming for the simultaneous realization of constant gain, accurate input and output impe... more ABSTRACT Aiming for the simultaneous realization of constant gain, accurate input and output impedance matching and minimum noise figure (NF) over a wide frequency range, the circuit topology and detailed design of wide broadband low noise amplifier (LNA) are presented in this paper. A novel 2.5–3.1 GHz wide-band LNA with unique characteristics has been presented. Its design and layout are done by TSMC 0.18µm technology. Common gate stage has been used to improve input matching. In order to enhance output matching and reduce the noise as well, a buffer stage is utilized. Mid-stages which tend to improve the gain and reverse isolation are exploited. The proposed LNA achieves a power gain of 15.9 dB, a NF of 3.5 dB with an input return loss less than−11.6, output return loss of−19.2 to−19 and reverse isolation of −38 dB. The LNA consumes 54.6 mW under a supply voltage of 2 V while having some acceptable characteristics.
Wireless Personal Communications, 2014
IEEE Transactions on Circuits and Systems I: Regular Papers, 2015
ABSTRACT The mammalian auditory system is able to process sounds over an extraordinarily large dy... more ABSTRACT The mammalian auditory system is able to process sounds over an extraordinarily large dynamic range, which makes it possible to extract information from very small changes both in sound amplitude and frequency. Evidently, response of the cochlea is essentially nonlinear, where it operates within Hopf bifurcation boundaries to maximize tuning and amplification. This paper presents a set of piecewise linear (PWL) and multipli-erless piecewise linear (MLPWL1 and MLPWL2) active cochlear models, which mimic a range of behaviors, similar to the biological cochlea. These proposed models show similar dynamical characteristics of the Hopf equation for the active nonlinear artificial cochlea. Accordingly, a compact model structure is proposed upon which a 2-D cochlea is developed. The proposed models are investigated, in terms of their digital realization and hardware cost, targeting large scale implementation. Hardware synthesis and physical implementation on a FPGA show that the proposed models can reproduce precise active cochlea behaviors with higher performance and considerably lower computational costs in comparison with the original model. Results indicate that the MLPWL1 model has a lower computational overhead, precision, and hardware cost, while the PWL model has a higher precision and dynamically tracks the original model. On the other hand, the MLPWL2 model outperforms the others in terms of accuracy, dynamical tracking of the original model and implementation cost. The gain variations of the original, PWL, MLPWL1, and MLPWL2 models are 230, 100, 105, and 230 dB, respectively. The mean normalized root mean square errors (NRMSEs) of the PWL, MLPWL1, and MLPWL2 models are 0.11%, 11.97%, and 0.34%, respectively, as compared to the original cochlear model.
Wireless Personal Communications, 2015
This paper discusses a novel multi-stub-loaded stepped-impedance resonator (MSLSIR) with a specif... more This paper discusses a novel multi-stub-loaded stepped-impedance resonator (MSLSIR) with a specific feeding structure. The fundamental and higher order modes of resonant frequencies of the stepped-impedance resonator are key parameters involved in the design of a dual-band bandpass filter (DBPF). However, since resonant frequencies are dependent on each other, the overall structure is not compact. The proposed MSLSIR has the advantage of flexible control over one resonant frequency while the other frequency is fixed. Furthermore, the utilization of isosceles right-angled triangular (IRT) and short-circuited stubs as loaded elements improves size miniaturization of DBPF when a low permittivity substrate is used. The analysis of the IRT stub is based on the coupling impedance formulas derived by integration of the associated Green‘s function. As an application, a DBPF is presented, which operates at 3.5 and 5.2 GHz, corresponding to the WiMAX and WLAN applications, respectively. In addition, a good stopband rejection, up to $$3\hbox {f}_{1}$$3f1, is obtained using the defected ground structure technique. An overall good agreement between the calculated, simulated and measured results is observed, thereby confirming the effectiveness of the proposed method.
2006 IEEE International Multitopic Conference, 2006
Substrate coupling noise is a key problem in today's large mixed-signal systems. This noise ... more Substrate coupling noise is a key problem in today's large mixed-signal systems. This noise is caused by the coupling of digital part and can perturb analog circuits through common substrate. The estimating and accurate modeling of noise coupling effects is a main challenge for designers. In this paper, we describe a method to quickly and accurately estimate substrate coupling effects based on Maxwell's equations and the integral solution for parasitic extraction. Examples are given which show that the proposed method is sufficiently accurate for practical circuit verification by avoiding a dense matrix storage and long computational runtime. Furthermore, a very good speedup factor is obtained when comparing our technique with other methods in the literature.
2010 International Conference on Electronic Devices, Systems and Applications, 2010
Substrate noise in integrated circuits is a major impediment to mixed-signal integration. Accurat... more Substrate noise in integrated circuits is a major impediment to mixed-signal integration. Accurate simulation is therefore, needed to investigate the generation, propagation, and impact of substrate noise. In this paper, we introduce novel substrate noise estimation and describe a fast and accurate simulator for modeling substrate coupling noise in mixed-signal RF IC design. Using a threedimensional finite element method for extraction of substrate parasitic elements is developed.
2010 International Conference on Electronic Devices, Systems and Applications, 2010
International Journal of Electronics Letters, 2013
ABSTRACT This article presents the design process, and analysis of a high-linearity, high-gain, l... more ABSTRACT This article presents the design process, and analysis of a high-linearity, high-gain, low-power and inductorless 3.1–4.8 GHz ultra-wideband (UWB) down conversion mixer in a 0.18 μm CMOS process with a 1.8 supply voltage. In the proposed structure, the linearity of the conventional Gilbert cell mixer is increased about 10 dBm without losing the conversion gain using the modified derivative superposition and current-bleeding techniques. Moreover, power consumption of the conventional mixer is significantly decreased. Besides, the conversion gain and S11 of the mixer are hand calculated and the validity of the analytical formulas is verified by simulation results.
Solar Energy Materials and Solar Cells, 2008
The temperature dependence of open-circuit voltage (V oc) and curve factor (CF) of a silicon sola... more The temperature dependence of open-circuit voltage (V oc) and curve factor (CF) of a silicon solar cell has been investigated in temperature range 295-320 K. The rate of decrease of V oc with temperature (T) is controlled by the values of the band gap energy (E g), shunt resistance (R sh) and their rates of change with T. We have found that R sh decreases nearly linearly with T and its affect on dV oc /dT is significant for cells having smaller R sh values. Series resistance also changes nearly linearly with voltage. CF depends not only on the value of R s and other parameters but also on the rate of change of R s with voltage. The rate of decrease of R s with voltage and T are important to estimate the value of CF and its decrease with temperature accurately.
Microwave and Optical Technology Letters, 2014
In this article, a novel compact microstrip dual-mode multistub-loaded stepped-impedance resonato... more In this article, a novel compact microstrip dual-mode multistub-loaded stepped-impedance resonator is introduced. Stepped-impedance resonator can be used for achieving the fundamental resonance frequency; however, the size of this structure is not compact and resonance frequencies are dependent. Utilizing multistubs as loaded elements improves size miniaturization with low permittivity substrate and brings the advantage of flexible controlling of one resonance frequency whereas the other one is fixed. As an application, a dual-band bandpass filter is presented to operate at 3.5 and 5.2 GHz, corresponding to the worldwide interoperability for microwave access and wireless local area network applications. An overall good agreement between the measured and simulated results is observed, confirming the proposed method. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1567–1570, 2014
Journal of Applied Sciences, 2008
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Papers by Gholamreza Karimi