Smart temperature sensors in CMOS with high uncalibrated accuracy (DCS.5668)

Temperature sensors with integrated interface electronics ('smart' temperature sensors) that are mass-produced in a CMOS process offer the advantages of low production costs and easy interfacing. However, their accuracy before calibration is limited to approximately ± 4°C over the temperature range of -50 to 150°C due to process spread and non-linearity. Present temperature calibration procedures are relatively expensive. This prevents the use of accurate low-cost temperature sensors in many applications where they would otherwise be desirable.

The primary goal of the project is to increase the accuracy that can be reached without calibration by a factor of 10. The fundamental limit to that accuracy will be investigated. Circuit techniques will be developed to compensate for the process spread and to reduce the non-linearity. The intention is to reach an accuracy of ± 0.4°C over the full temperature range. The secondary goal is to develop low-cost calibration techniques. The intention is to further improve the accuracy to ± 0.1°C over the full temperature range.

The methods and techniques developed for temperature sensors can also be applied elsewhere. For instance, the accuracy of bandgap references, wich are currently the most commonly applied integrated voltage references, is limited by the same factors as the accuracy of temperature sensors. Therefore, the techniques developed to improve temperature sensors are also applicable to bandgrap references. In addition, the calibration and auto-correction techniques developed for temperature sensors could also be applicable to other sensors, such as pressure sensors.

The most commonly applied temperature sensors in industrial applications are platinum resistors. Compared to platinum resistors, CMOS smart temperature sensors cost less and are easier to use. Their use reduces the system complexity, because they need less interface electronics and can communicate directly with a microcontroller via a standardized interface. However, currently their accuracy cannot compete with that of platinum resistors, unless an expensive calibration at multiple temperatures is performed.

The results of the proposed project will allow the production of CMOS smart temperature sensors with a much higher accuracy, wich will open up a huge market. For moderate-accuracy applications, it will be possible to use uncalibrated sensors, wich will significantly lower production costs. For high-accuracy applications, the new calibration techniques will reduce the cost of calibration by lowering the requirements of the calibration setup, and will improve the accuracy of the calibration.

Sensor manufacturers will be able to apply the results in their temperature sensors, but also in other products that need a temperature sensor as a subblock, such as pressure sensors with temperature compensation. The availability of low-cost high-accuracy smart temperature sensors will allow companies to reduce the costs and complexity of existing products and enable the application of temperature sensors in new products.

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