Power requirements, catalytic sensors

One of the most common types of gas sensor sold is the electrochemical gas sensor however, although these are low power, it is not possible to integrate this type of sensor and the necessary circuits on the same chip. This is because it requires signihcant volumes of liquid electrolytes and non-CMOS catalytic materials, such as platinum or silver electrodes. Another common gas sensor is based on infrared absorption but these require high power for the source and non-CMOS optical band-pass filters. They are also even more expensive than electrochemical sensors at 50 or more. 

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