Yasir Karisan

Range Estimation in Multicarrier Systems in the Presence of Interference: Performance Limits and Optimal Signal Design

Theoretical limits on time-of-arrival (equivalently, range) estimation are derived for multicarrier systems in the presence of interference. Specifically, closed-form expressions are obtained for Cramer-Rao bounds (CRBs) in various scenarios. In addition, based on CRB expressions, an optimal power allocation (or, spectrum shaping) strategy is proposed. This strategy considers the constraints not only from the sensed interference level but also from the regulatory emission mask. Numerical results are presented to illustrate the improvements achievable with the optimal power allocation scheme, and a maximum likelihood time-of-arrival estimation algorithm is studied to assess the effects of the proposed approach in practical estimators.

Lumped-Element Equivalent-Circuit Modeling of Millimeter-Wave HEMT Parasitics Through Full-Wave Electromagnetic Analysis

We present a broadband lumped-element parasitic equivalent circuit to accurately capture the frequency response of electromagnetic (EM) interactions inside the structure and surrounding environment of high electron-mobility transistors (HEMTs). A new mutual inductance term is included to account for the high-frequency magnetic field coupling between device electrodes. An analytical method is also proposed, for the first time, to extract the gate-to-drain mutual inductance LMGD, which creates an undesirable inductive feedback path from output to input at millimeter wavelengths. Based on the suggested extrinsic equivalent circuit, we propose a novel multistep parameter extraction procedure that utilizes direct analytic extraction and linear regression techniques systematically to determine the parasitic component values. The accuracy and robustness of the presented extraction algorithm are established via comprehensive comparisons between EM simulations, measurements, and frequency responses of the suggested equivalent circuits up to and beyond 300 GHz in the millimeter-wave (mmW) band. The key parasitic elements that are most detrimental to the microwave performance are identified and optimized through subsequent circuit analysis. Design guidelines are provided for optimum device layout selection to achieve the highest frequency performance. It is demonstrated through a full-wave simulation based parametric study that around 20% improvement in maximum oscillation frequency is achievable via optimization of device gate finger number and unit finger width.

Performance Limits on Ranging with Cognitive Radio

Cognitive radio is a promising paradigm for efficient utilization of the radio spectrum due to its capability to sense environmental conditions and adapt its communication and localization features. In this paper, the theoretical limits on time-of-arrival estimation for cognitive radio localization systems are derived in the presence of interference. In addition, an optimal spectrum allocation strategy which provides the best ranging accuracy limits is proposed. The strategy accounts for the constraints from the sensed interference level as well as from the regulatory emission mask. Numerical results are presented to illustrate the improvements that can be achieved by the proposed approach.

Distributed modeling of submillimeter-wave HEMT parasitics based on full-wave electromagnetic analysis

We present a broadband distributed parasitic equivalent circuit model to accurately reproduce the frequency response of electromagnetic (EM) field couplings within the structure of submillimeter-wave (sub-mmW) high electron mobility transistors (HEMTs) in terahertz (THz) band. We also develop a novel systematic multi-step parameter extraction algorithm. The accuracy of the suggested extraction procedure is validated through extensive comparisons between full-wave (FW) simulated, measured, and modeled frequency responses of the presented test standards up to 750 GHz.

Lumped-Element Modeling of Millimeter-Wave HEMT Parasitics via Full-Wave Electromagnetic Analysis

We present a broadband lumped-element parasitic equivalent circuit extraction procedure based on full-wave modeling of electromagnetic interactions within the pad layout of millimeter-wave (mmW) high electron mobility transistors (HEMTs). The proposed method is illustrated using a conventional two-finger HEMT topology within a coplanar waveguide environment. The accuracy of the suggested extraction procedure is validated through extensive comparisons between full-wave electromagnetic simulations, measured data, and the computed response of the proposed model up to 325 GHz. Using the proposed approach, we are also illustrating the impact of the gate-to-drain mutual inductance introduced in the conventional small signal equivalent circuit. Subsequently, we apply our new approach to differential configurations.

Full-wave electromagnetic modeling of sub-millimeter wave HEMT parasitics

We present a new distributed parasitic equivalent circuit model to accurately reproduce the frequency response of electromagnetic field couplings within the structure of submillimeter-wave high electron mobility transistors in the millimeter-wave and terahertz bands. To construct the proposed circuit model, we develop a multi-step parameter extraction algorithm, and demonstrate its accuracy through comprehensive comparisons between full-wave simulated, measured and modeled frequency responses of the presented test patterns up to 750 GHz.

Extraction of parasitics in GaN HEMTs via Full-Wave Electromagnetic Modeling

We present a new equivalent circuit model for millimeter-wave and sub-millimeter wave GaN high electron mobility transistors (HEMTs) that can capture the geometry-and material-dependent parasitic effects within the device. The impact of electromagnetic interactions on overall device performance is analyzed extensively via full-wave EM simulations using high-fidelity device geometries. An empirical lumped-element equivalent circuit model is developed to capture the electromagnetic behavior not only within the internal structure of the device but also the surrounding impedance environment. Based on this parasitic-aware equivalent circuit, a multiple-step parameter extraction algorithm is employed to determine the equivalent lumped elements. Numerical results, using a conventional sub-mmW HEMT topology are presented to illustrate the performance of the proposed circuit models in capturing device physics in the THz band.

Full-wave modeling device parasitics of sub-millimeter wave HEMTs

Extrinsic parasitic couplings of millimeter-wave and submillimeter-wave high electron mobility transistors (HEMTs) are investigated in the context of THz integrated circuits. More specifically, a multiple-step HEMT parasitic extraction procedure, aimed at improving device performance in the THz band, is developed. A distributed circuit model of lossy substrate is introduced to better approximate the propagation and attenuation through the mesa of the device. Intrinsic and extrinsic effects are considered independently to clearly identify the factors impacting high frequency operation. Numerical examples, involving a submmW HEMT are presented to illustrate the working mechanism of the proposed characterization technique.

Lumped-element modeling of millimeter-wave HEMT parasitics via full-wave electromagnetic analysis

We present a broadband lumped-element parasitic equivalent circuit extraction procedure based on full-wave modeling of electromagnetic interactions within the pad layout of millimeter-wave high electron mobility transistors (HEMTs). The proposed method is illustrated using a conventional two-finger HEMT topology within a coplanar waveguide environment. The accuracy of the suggested extraction procedure is validated through extensive comparisons between full-wave electromagnetic simulations, and the computed response of the proposed model up to 325 GHz. For the first time, we develop a systematic parameter extraction algorithm for differential device configurations.

Wideband impedance-matched integrated transceivers for future THz-band wireless networks

The explosive growth in personal wireless connectivity is rapidly consuming the available spectrum in the RF and microwave bands. Major service providers and consumer electronics manufacturers are already investing in the millimeter wave band to develop transceivers to accommodate extremely large data rates needed for high-speed inter-device connectivity. It is not surprising that the next frontier in wireless spectrum utility will be the THz band.