José L. Chávez-Hurtado

Polynomial-based surrogate modeling of microwave structures in frequency domain exploiting the multinomial theorem

We propose a methodology for developing EM-based polynomial surrogate models exploiting the multinomial theorem. Our methodology is compared against four EM surrogate modeling techniques: response surface modeling, support vector machines, generalized regression neural networks, and Kriging. Results show that the proposed polynomial surrogate modeling approach has the best performance among these techniques when using a very small amount of learning base points. The proposed methodology is illustrated by developing a surrogate model for a T-slot PIFA antenna simulated on a commercially available 3D FEM simulator.

Polynomial-Based Surrogate Modeling of RF and Microwave Circuits in Frequency Domain Exploiting the Multinomial Theorem

A general formulation to develop electromagnetic-based polynomial surrogate models in the frequency domain utilizing the multinomial theorem is presented in this paper. Our approach is especially suitable when the number of learning samples is very limited and no physics-based coarse model is available. We compare our methodology against four other surrogate modeling techniques: response surface modeling, support vector machines, generalized regression neural networks, and Kriging. Results confirm that our modeling approach has the best performance among these techniques when using a very small amount of learning base points on relatively small modeling regions. We illustrate our technique by developing a surrogate model for a substrate integrated waveguide interconnect with transitions to microstrip lines, a dual-band T-slot planar inverted-F handset antenna, and a high-speed package interconnect. Examples are simulated on a commercially available 3-D FEM simulator.

Enhanced formulation for polynomial-based surrogate modeling of microwave structures in frequency domain

Practical formulations for EM-based modeling of microwave structures using simple polynomial surrogate functionals are described in this paper. A new polynomial surrogate formulation is proposed and compared against a previously published formulation. Both formulations calculate the surrogate model weighting factors in closed form, yielding global optimal values in the least squares sense. These formulations are suitable for EM-based design problems with no equivalent circuital models available. Our new formulation exhibits smaller learning errors and better generalization performance than the original formulation. Both methodologies are illustrated by the EM-based modeling a SIW interconnect with microstrip transitions on a standard FR4-based substrate implemented in a 3D full-wave FEM simulator.

Multiphysics polynomial-based surrogate modeling of microwave structures in frequency domain

A formulation to develop polynomial surrogate models for high frequency structures subject to multiphysics variations in the frequency domain is presented in this paper. The original fine model considers the mechanical stress and the electromagnetic (EM) effects caused by changes in circuit temperature. These effects are calculated in a FEM-based simulator for which we define the electro-thermo-mechanical properties of the metallic and dielectric materials involved. We illustrate our technique by developing a polynomial surrogate model of a microstrip line implemented in COMSOL, where the circuit temperature is varied from −20 to 180 Celsius degrees. Obtained results show a very good match between the multiphysical fine model and the corresponding surrogate.

Reliable full-wave EM simulation of a single-layer SIW interconnect with transitions to microstrip lines

We present a procedure to obtain reliable EM responses for a substrate integrated waveguide (SIW) interconnect with microstrip line transitions. The procedure focuses on two COMSOL configuration settings: meshing sizes and simulation bounding box. Once both are properly configured, the implemented structure is tested by perturbing the simulation bounding box to assure it has no effect on the EM responses

Reconfigurable FIR filter coefficient optimization in post-silicon validation to improve eye diagram for optical interconnects

Enhanced small form-factor pluggable (SFP+) is a specification for a new generation of optical modular transceivers. The devices are designed for use with small form factor (SFF) connectors, and offer high speed and physical compactness. SFP+ modules require high-quality ASIC/SerDes transmitters (Tx) because IEEE and fibre channel standards place strict requirements on the optical interface, and linear/limiting SFP+ module types have Tx paths that do not correct for timing jitter. This introduces a design challenge to guarantee performance over process, temperature, and voltage (PVT) conditions. Adjusting the Tx equalization across PVT and different interconnect channels can be a time-consuming task in post-silicon validation. In order to overcome this problem, this paper proposes a direct optimization method based on a suitable objective function formulation to efficiently tune the Tx equalizer and optimize the eye diagram to successfully comply with industrial specifications.

System Margining Surrogate-Based Optimization in Post-Silicon Validation

There is an increasingly higher number of mixed-signal circuits within microprocessors. A significant portion of them corresponds to high-speed input/output (HSIO) links. Post-silicon validation of HSIO links is critical to provide a release qualification decision. One of the major challenges in HSIO electrical validation is the physical layer (PHY) tuning process, where equalization techniques are typically used to cancel any undesired effect. Current industrial practices for PHY tuning in HSIO links are very time-consuming, since they require massive laboratory measurements. On the other hand, surrogate modeling techniques allow to develop an approximation of a system response within a design space of interest. In this paper, we analyze several surrogate modeling methods and design of experiments techniques to identify the best approach to efficiently optimize a receiver equalizer. We evaluate the models performance by comparing with actual measured responses on a real server HSIO link. We then perform a surrogate-based optimization on the best model to obtain the optimal PHY tuning settings of an HSIO link. Our methodology is validated by measuring the real functional eye diagram of the physical system using the optimal surrogate model solution.

Enhanced procedure to setup the simulation bounding box and the meshing scheme of a 3D finite element EM simulator for planar microwave structures

We present an enhanced procedure to properly configure the simulation bounding box and discretization meshing scheme of a 3-D finite element full-wave EM simulator as applied to planar microwave circuits. Our procedure utilizes a meshing scheme that takes into account not only the wavelength at the highest simulated frequency, but also the geometrical objects associated to the simulated structure, as well as the expected physics behavior. We demonstrate how our physics-based meshing significantly improves the expected EM behavior of planar structures and decreases their sensitivity to the simulation bounding box, with respect to the conventional meshing scheme based on volumetric domains. We also show how a reasonable but inadequate meshing reduces the possibility of success when using direct optimization on the planar structure and makes the optimization process computationally more expensive. Our procedure is illustrated by a fifth order bandstop microstrip filter with L-shaped resonators simulated with COMSOL.

Design of reusable CMOS OTAs using CAD tools

In this paper an automation tool is proposed for OTA designs. The core of the tool is a combination of a mathematical tool and a circuit simulator. The automation tool contains four libraries: OTA topologies, technology parameters, performance limits and design constraints. Design of typical OTA topologies can be implemented in three fabrication technologies. The user introduces OTA specifications and the automation tool looks for the best OTA structure considering the cheapest fabrication technology available in the library, and delivers a sized circuit that fulfills design specifications. Our automation tool is illustrated by a complete design flow of an FDFC with CMFB OTA in AMIS 0.5 µm CMOS technology.