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|Performance Considerations for Precision Analog Signal Conditioning Semiconductors in Very High Temperature Environments|
|Keywords: High Temperature, Amplifier, Voltage Reference|
|When designing signal chains for systems exposed to high temperature environments, analog signal processing ICs, such as operational amplifiers and references, are needed to enable precision sensor measurements. However, as ambient operating temperatures increase beyond the typical extended-industrial +125˚C limit, the characteristics of modern, monolithic, analog semiconductors are strongly impacted by the effects of temperature on the both the circuit design and the underlying fabrication process. Semiconductor device physics comes into play as temperature influences the matching of components in the bias networks, input & output devices, and ESD protection cells, all of which exact a toll on performance. These effects primarily follow the classical p-n diode performance curve at elevated temps, generating lower breakdowns, higher currents, and changing circuit operating points. Commonly the output load drive degrades and input offset variation increases while in some cases parameters such as input bias current and bandwidth actually improve. In this paper we explore what changes occur in precision op amp performance as temperature increases beyond 125°C, going to 175°C and then to 210°C. We discuss steps taken to ensure amplifier initial performance at high temperature is robust and can be maintained over a limited lifetime. We then introduce two new products rated for high temperature operation, a high temp rated op amp and voltage reference, which are both key components necessary to design complete signal chains. In conclusion, we demonstrate how performance shifts over temperature impact an example application: the amplifier and reference are used in the design of a constant current source driving a sensor, with same amplifier also being used to provide the sensor interface for downstream circuits in the signal chain.|
|Jeff Watson, Systems Applications Engineer