Characterization of Circuit Blocks for Configurable Analog-Front-End

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Analog functions have been implemented in a Silicon-on-Insulator (SOI) process optimized for high-temperature (>225°C) operation. These include a linear regulator/reference block that supports input voltages up to 50V and provides multiple independent voltage outputs. Additional blocks provide configurable sensor excitation levels of up to 10V DC and/or 20V AC-differential, with current limiting and monitoring. A dual-channel Programmable-Gain-Instrumentation Amplifier (PGIA) and a high-level AC input block with programmable gain and offset serve signal conditioning, gain, and scaling needs. A multiplexer and analog buffer provide an output that is scaled and centered for down-stream A-to-D conversion. Limited component availability and high component counts deter development of sensing and control electronics for extreme temperature (>200°) applications. Systems require front-end power conditioning, sensor excitation and monitoring, response amplification, scaling, and multiplexing. Back-end Analog-to-Digital conversion and digital processing/control can be implemented using one or two integrated circuit chips, whereas the front-end functions require component counts in the dozens. The low level of integration in the available portfolio of SOI devices results in high component count when constructing signal conditioning interfaces for aerospace sensors. These include quasi-DC sensors such as thermo-couples, strain-gauges, bridge transducers as well as AC-coupled sensors and position transducers, such as Linear Variable Differential Transducers (LVDT's). Furthermore, a majority of sensor applications are best served by excitation/response voltage ranges that typically exceed the voltage range of digital electronics (either 5V or 3.3V in currently available digital IC's for use above 200°C). These constraints led Embedded Systems LLC to design a generic device which was implemented by Honeywell as an analog ASIC (Application Specific Integrated Circuit). This paper will describe the ASIC block-level capabilities in the context of the typical applications and present characterization data from wafer-level testing at the target temperature range (225C). This material is based upon work performed by Honeywell International under a subcontract from Embedded Systems LLC, funding for which was provided by the U.S. Air Force Small Business Innovative Research program.