Anjan Chakravorty

An existing water distribution network (WDN) may need to be expanded by adding a sub-network for the newly developed areas. The size of the problem becomes larger when the stochastic nature of domestic demands, optimal design and layouts, control, and operation of various hydraulic components are considered. In this study, the single-port Thevenin theorem used in electrical circuits is applied to reduce a large WDN with its equivalent network consisting of a single source and a single pipe. The equivalent network is then attached to a sub-network for focused analysis. The accuracy and robustness of the proposed network reduction procedure are investigated on realistic WDNs for various sub-network demands using steady and extended period simulations. A simplified approach is also presented to achieve the same objective but constrained by the level of accuracy. Hydraulic engineers can use the proposed methodology as an efficient network reduction tool.

In this part, we propose a step-by-step strategy to model the static thermal coupling factors between the fingers in a silicon based multifinger bipolar transistor structure. First we provide a physics-based formulation to find out the coupling factors in a multifinger structure having no-trench isolation (cij,nt). As a second step, using the value of cij,nt, we propose a formulation to estimate the coupling factor in a multifinger structure having only shallow trench isolations (cij,st). Finally, the coupling factor model for a deep and shallow trench isolated multifinger device (cij,dt) is presented. The proposed modeling technique takes as inputs the dimensions of emitter fingers, shallow and deep trench isolations, their relative locations and the temperature dependent material thermal conductivity. Coupling coefficients obtained from the model are validated against 3D TCAD simulations of multifinger bipolar transistors with and without trench isolations. Geometry scalability of the model is also demonstrated.

In this article, the effect of charge partitioning in a silicon-on-insulator lateral double-diffused metal-oxide-semiconductor (LDMOS) transistor on its nonlinearity model is investigated. It is found that the prediction of the third-order intermodulation distortion (IM3) depends on the model equivalent circuit (EC) and appropriate charge assignments at various nodes therein. The investigation is carried out using a highly accurate static model of LDMOS along with a couple of different charge-partitioning schemes in order to single out their effects on the nonlinearity model behavior. We observe that charge partitioning in a more flexible EC framework yields an improved IM3 prediction when compared with the TCAD simulated results.

A modified physics-based two-section model is proposed to accurately capture the lateral non-quasi-static effect in SiGe HBTs. A methodology is proposed to include the DC emitter current crowding effect in the existing two-section model framework. The proposed two-section model is implemented in Verilog-A. The large-signal transient and the small-signal AC simulations are carried out and the results are compared with the numerical device simulation data. The proposed model is observed to perform better than the existing two-section model and the state-of-the-art standard model from the perspectives of small-signal frequency-domain characteristics and large-signal transients.

In this brief, we propose a step-by-step strategy to accurately estimate the finger temperature in a silicon-based multifinger bipolar transistor structure from conventional measurements. First we extract the nearly zero-power self-heating resistances (Rth,ii (Ta)) and thermal coupling factors (cij (Ta)) at a given ambient temperature. Now, by applying the superposition principle on these variables at nearly zero-power, where the linearity of the heat diffusion equation is preserved, we estimate an effective thermal resistance (Rth,i (Ta)) and the corresponding revised finger temperature Ti (Ta). Finally, the Kirchhoff's transformation on Ti (Ta) yields the true temperature at each finger (Ti (Ta,Pd)). The proposed extraction technique automatically includes the effects of back-end-of-line metal layers and different types of trenches present within the transistor structure. The technique is first validated against 3-D TCAD simulation results of bipolar transistors with different emitter dimensions and then applied on actual measured data obtained from the state-of-the-art multifinger SiGe HBT from STMicroelectronics B5T technology. It is observed that the superposition of raw measured data at around 40 mW power underestimates the true finger temperature by around 10%.

The boundaries of existing cities are expanding rapidly due to the exponential growth in urban population. Therefore, the existing water distribution networks (WDNs) need to be expanded up to the newly developed areas to meet the additional water demand. The optimal design of a sub-network planned for network expansion requires multiple simulations under various constraints. Simulating the additional sub-network along with the existing network takes a lot of CPU time. In this study, a methodology is proposed to replace an existing large pipe network with its equivalent network consisting of a single source and a single pipe by applying the non-linear Thevenin theorem being used for electrical circuits. The equivalent network model parameters are extracted by fitting the driving-node head-loss characteristics at the connecting node. Unlike all other available methods except the traditionally used reservoir–pump model, the equivalent network presented in this study reduces to only two elements. The theoretical aspect of the reservoir–pump model can be explained by the proposed Thevenin reduction method. The advantage of the proposed method is put forward by deriving an analytical expression for the condition of maximum power transfer from the equivalent main network to the sub-network. The economic diameter value of the connecting pipe is subsequently determined. The proposed network reduction method is demonstrated on different WDNs for various demand patterns. The reduced networks yield accurate results and simulate faster when compared with those of the original networks. The proposed methodology is beneficial for a focused analysis of a sub-network and to transfer maximum power to the sub-network connected to a large existing hydraulic network.

Terahertz (THz) silicon-based electronics is undergoing rapid developments. In order to keep this momentum high, an accurate and optimized on-wafer characterization procedure needs to be developed. While evaluating passive elements, the measured s-parameter data can be verified by a direct use of EM simulation tools. However, this verification requires to precisely introduce part of the measurement environment such as the probes, pads, and access lines to accurately predict the impact of calibration and layout for on-wafer measurements. Unfortunately, this procedure is limited to passive elements. Hence, in this work, we propose a new procedure to emulate the measurement of active devices using an electromagnetic SPICE cosimulation. By this method, one can clearly highlight that a measurement artifact that was observed for the transistor measurement can be reproduced. One of the most representative examples of measurement artifact involves the measurement and estimation of ${f}_{\text {MAX}}$ which is not constant over all frequency bands. Also, the measurement is difficult to perform above 40 GHz. This typical problem is now undoubtedly attributed to the probe-to-substrate coupling and probe-to-probe coupling which are strongly dependent on the probe geometry. Finally, this cosimulation procedure evidently underlines the need for an optimized deembedding procedure above 200 GHz.

We propose a physics-based analytical model that accurately captures the effects of buffer traps on dc characteristics of gallium nitride (GaN)-based high-electron-mobility transistors (HEMTs). The model is then semi-analytically extended to additionally include the transient behavior. Analytical formulations for the shift in the threshold voltage ${(}{V}_{\text {OFF}}{)}$ and two-dimensional electron gas (2-DEG) density due to the presence of buffer traps in the steady state are presented. In pulsed operation, technology computer-aided design (TCAD) simulations indicate that a time-dependent negative potential (NP) is developed under the gate, resulting in a modified ${V}_{\text {OFF}}$ and current collapse (CC). An expression for the modified ${V}_{\text {off}}$ helps capture the pulsed current-voltage characteristics. The model captures the dependence of bias, time, temperature, trap concentration, capture cross section area, and activation energy of traps on the steady-state and transient characteristics. The model is implemented in Verilog-A in an existing compact model framework using a diode and RC sub-circuit and validated using measured data and TCAD simulations. The modeling results are in excellent agreement with the experimental data and TCAD simulations. Since the model is physics-based, it requires fewer number of parameters compared to that in the existing models.

Due to rapid urbanization, the existing water distribution networks need to be expanded by adding sub-networks for the newly developed areas. The stochastic nature of demands requires several simulations of the full network for optimum design and cost minimization. The size of the simulation problem thus becomes complex and computationally expensive. The reduced models can be handy for designing and optimizing such networks. This paper describes the usage of equivalent electrical circuit theory to reduce a large water distribution network for focussed analysis of a sub-network. Two methodologies are proposed to obtain the equivalent network using linear and nonlinear forms of the Thevenin theorem. Unlike other network reduction methods, the reduced equivalent networks derived from these methodologies have only two elements, such as a reservoir and an equivalent pipe for the existing network. In the first method, the nonlinear pipe network is replaced and implemented with its analogous linear electrical network in a circuit simulator for finding open circuit voltage and short circuit current at the desired node and branch. The equivalent pipe network parameters are estimated using these values. In the second method, the equivalent network parameters are extracted by ffitting the driving point headloss characteristics at the desired node with a suitable headloss formula. Applicability and comparison of the proposed network reduction methodologies are demonstrated on a realistic water distribution network connected with a sub-network. The simulated results of the reduced networks are compared with the solutions of the original nonlinear network. The reduced network obtained from the second method is found to yield more accurate results than the first method when the driving point headloss characteristic curve is fitted accurately. The reduced networks can be solved in much less computation cost than the original network. Therefore, the proposed network reduction methodologies are beneficial for analyzing a focused part, i.e. sub-network, of a large pipe network with stochastic demands in much less computational effort.

Expansion and reorganization of water distribution networks by connecting sub-networks via single or multiple pipes are common practices in developing cities to serve newly developed areas. In that context, the existing large network is often replaced with its equivalent simplified network for the optimal design of the upcoming sub-networks to avoid the computational burden. The reservoir-pump model is frequently used by practicing hydraulic engineers to replace an existing one; however, such a model should be applied only when the networks are connected through a single pipe. In this study, a new network reduction methodology is developed for multi-port connections utilizing the analogy between electrical circuits and hydraulic networks. The equivalent simple network is obtained by suitably applying the generalized Thevenin theorem for electrical circuits. The number of network elements in the equivalent network is significantly reduced compared to the ones obtained by the existing water distribution network (WDN) reduction methods. Therefore, it is possible to reorganize and expand a large existing network system from a prior knowledge of its most sensitive parts. The accuracy and robustness of the proposed methodology are investigated on realistic WDNs by comparing the results with EPANET, for both Demand Driven Analysis and Pressure Driven Analysis. However, as of now, an electrical simulator is required to implement the proposed methodology due to the absence of current dependent voltage source model in hydraulic simulators. The proposed network reduction method can be of enormous utility for hydraulic engineers and opens up an opportunity to implement new elements in hydraulic simulators.