Modeling Multipliers through Terahertz Frequencies

Terahertz frequency bands support short-range communications at high data rates. Designing transmitters and receivers at those higher frequencies requires command of the gallium arsenide (GaAs) Schottky barrier diodes that are capable of multiplying microwave signals into the THz range. Fortunately, lumped-element-equivalent-circuit (LEC) models have been developed to aid the design of planar GaAs Schottky diode frequency multipliers and mixers operating at frequencies to 3 THz. These models are relatively simple and straightforward and function with commercial computer-aided-design (CAD) software simulation tools. They have been used in the design and development of multipliers operating into the THz frequency region.

In addition to LEC models, physics-based models have been used to simulate the carrier transport in GaAs Schottky diodes based on predictions using the Boltzmann transport equation (BTE) and Poisson’s equation Another model for high-frequency circuits, the Monte Carlo (MC) model, is based on the microscopic modeling of the interactions of the Schottky charge carriers with the device’s crystal lattice and external fields. This approach has shown to be accurate for describing physical phenomena through THz frequencies; it has been used as a reference model for these THz simulations.

To better understand modeling and computer simulations of Schottky diodes and frequency multipliers operating through the THz frequency range, a group of researchers from the Technical University of Madrid (Madrid Spain)—Diego Pardo, Jesus Grajal, Carlos G. Perez-Moreno, and Susana Perez—performed a comparison of model predictions with measurements performed on diode multipliers designed and fabricated by the Jet Propulsion Laboratory (JPL) for frequencies from 200 to 2700 GHz. In many cases, combinations of computer simulators, such as an LEC model in conjunction with a three-dimensional (3D) electromagnetic (EM) simulator, was used to model the nonlinear behavior of a Schottky diode.

A number of different devices were modeled, including frequency doublers through 1.5 THz, frequency triplers through 2.7 THz, and frequency multipliers with Schottky diodes operating past 3 THz. Comparison of simulations with measured results reveal that the models offer different levels of accuracy under different conditions, with the MC model shining in most cases. See “An Assessment of Available Models for the Design of Schottky-Based Multipliers Up To THz Frequencies,” IEEE Transactions on Terahertz Science and Technology, March 2014, p. 277.

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