During the development of the Soil Moisture Active-Passive (SMAP) High-Power Amplifier (HPA), a power glitch was observed with the characteristic of producing small 0.1-0.3 dB jumps in power across temperature. In order to troubleshoot this glitch behavior, a nonlinear model that could describe the saturation behavior of the HPA across temperature was desired. However, nonlinear device models were not available for the transistors and components within the HPA. Measured data of the HPA subassemblies were available but were of various formats, including s-parameters, nonlinear pin-pout curves, and fixed losses over temperature, and not easily modeled within commercial EDA (electronic design automation) simulation tools. This tool was built to be able to understand the gain/power distribution stackup and the sensitivities to power changes in the HPA over temperature.

This tool allows the import of s-pa - ram eters, pin-pout curves, fixed losses over temperature, and equation-based models. In addition, the software can easily be extended to additional data types. The tool allows the user to simulate the model over frequency, power, and temperature given if those parameters are within the measured data. The software is scalable and can handle many different types of measured data formats. The software will also interpolate data points based on the parameter set available. A key feature of this tool is the ability to simulate and model the system without a full dataset for all of the components in the RF chain.

To understand the extensibility of this software tool, it was repurposed for the next-generation Mars rover landing radar system to simulate the RFEA (RF Electronics Assembly) system chain. This next-generation Mars rover, known as “Mars 2020,” is a build-to-print of the Mars Science Laboratory’s (MSL) and uses the same spacecraft, avionics, and flight systems. Given the unit-to-unit variation between the MSL UDA (Up/Down Converter Assembly) and the spare that is the baseline to be used for the Mars 2020 rover, there was concern that the UDA for the new Mars 2020 rover would not have enough power to drive the transmit/receive modules (TRMs) into saturation over temperature. The simulation was performed and showed that at 50 °C, the power dropped to slightly lower than what is needed. Further simulations and measurements show that this degradation is expected to have little impact on system performance.

These simulations could not be performed using existing EDA tools because these tools have limited ability to use a wide range of data types and formats, with sometimes incomplete data sets. This tool allows estimated performance to be calculated, and interpolates as needed if the data is not available. Most EDA programs require complete data sets for all blocks in order to be modeled accurately. While care should be taken to understand the deficiencies in the datasets provided since not all data can always be measured or accurately modeled within a system, this tool allows insight into building a full system model.

This work was done by Tushar Thrivikraman of Caltech for NASA’s Jet Propulsion Laboratory. This software is available for license through the Jet Propulsion Laboratory, and you may request a license at: https://download.jpl.nasa.gov/ops/request/request_introduction.cfm . NPO-49742

NASA Tech Briefs Magazine

This article first appeared in the May, 2016 issue of NASA Tech Briefs Magazine.

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