CMOS thermoelectric sensor interfaces

Thermoelectric sensors are promising devices for measuring different physical quantities, such as infrared radiation, temperature, gas flow or AC power, in many application areas. Recent developments in the research of integrated microsensors, demonstrated the possibility of fabricating thermoelectric sensors using stan¬ dard CMOS technologies. Of course, the materials available in a CMOS process are limited and their thermoelectric properties may not be optimal. Therefore, CMOS compatible thermoelectric sensors are typically less performant than devices based on dedicated materials. The possibility of integrating the sensor and the interface circuit on the same chip, however, can possibly overcome these lim¬ itations, allowing to achieve competitive performance. Moreover, all the advan¬ tages of a fully integrated system become available. The size of the complete sensor system can be reduced and the reliability increased. Sophisticated on-chip signal processing functions can further improve the performance of the sensor and, finally, batch fabrication allows low production costs. This thesis reports on the design of interface circuits for integrated thermoelectric sensors. In particular we consider three different devices, namely an infrared sen¬ sor, an AC power sensor or thermal converter and a multisensor for heating, ven¬ tilation and air conditioning (HVAC). All of these require quite unconventional and challenging interface circuits, which, nevertheless, have an application poten¬ tial for industrial products. The thermoelectric infrared sensor is intended for intrusion alarm systems. In this application the sensor has to detect the infrared radiation produced by the human body, in order to identify the presence of an intruder in a building. Due to the low radiation power involved, the signal produced by the sensor is very weak (few tens of |0,V). Noise is, therefore, by far the most critical constraint in the design of the interface circuit. Exploiting the auto-zero technique to reduce the flicker noise of MOS transistors, we designed an amplifier with variable gain and total input referred noise lower than 1 \iV (integrated over the band 0.1 to 10 Hz).