Starting from the twentieth century, climate change have progressively become the most dangerous threat to life on Earth. Some of its effects, like air pollution, have led to the development of devices, called gas sensors, that are able to monitor the presence of substances that could be harmful or toxic for human health. From a technological and electrical point of view, a constraint about sensors is their difficult compatibility with CMOS electronic systems which they interact with. Since full integration on CMOS circuits is complicated to achieve, the best compromise consists in designing circuits that have the task of properly conditioning the sensor and convert the detection information into electrical signals.