A Low-Power CMOS Wind Sensor

Abstract

This work describes a low-power and low-cost alternative to mechanical wind sensors, suitable for volume production in standard CMOS processes. The CMOS wind sensor operates in the electro-thermal domain; therefore, it has no moving parts and therefore requires very little maintenance. Moreover, the CMOS wind sensor is an active sensor, compared to its mechanical counterpart. Its sensitivity can be easily adjusted by changing the magnitude of the excitation signal.

Despite the manufacturing advantages of CMOS technology, the wind sensor has not attained commercial success in the market. This is due, in part, to process spread and packaging artifacts that have resulted in offset, nonlinearity and angle errors in detecting wind speed and direction. Because of this, expensive manual calibration is required to compensate these errors. Furthermore, its power consumption, in the order of tens of milliwatts, is not yet low enough to compete with its MEMS counterparts.

In this thesis, the design of a new version of the wind sensor is described, which aims to address the drawbacks of previous designs. Four extra resistors were added at each corner to electrically compensate for packaging artifacts, with the aim of reducing calibration costs. Larger thermopiles (a number of thermo- couples in series) were used, resulting in a greater signal-to-noise ratio (SNR). Internal signals were buffered to output pads to gain more insight into the magnitude of the sensor's internal signal swings. With these improvements, the resulting wind sensor chip consumes less than 30 mW of heating power and has an accuracy of ±0.6 m/s (speed) for wind speeds ranging from 1 to 25 m/s, and ±2.5°(direction) for a range of 4 to 25 m/s.