A smart compass sensor has been developed in standard CMOS with integrated signal conditioning and interface electronics. The compass sensors measure the horizontal components of the earth's magnetic field, which has a typical field strength of 25¿T. The sensor's offset is 4¿T (3¿), and its offset stability is less than 0.25¿T/week. Due to this low offset stability, the detection level is only limited by system noise. By using an improved chopper amplifier in the front-end the system noise has been reduced to 0.12¿T/¿Hz. In order to measure all three components of the earth's magnetic field, each sensor is packaged in a custom SFN8 package, which enables the necessary orthogonal alignment of three sensors. The presented 3D sensor module consists of three daisy-chained sensors, and illustrates the ease-of-use of a smart sensor with integrated bus (SPI/¿wire) interface. Apart from a single decoupling capacitor, no external components are necessary to read out the sensor signals, which reduces system costs.@en

Smart sensors are systems in which sensors and dedicated interface electronics are integrated on the same chip, or at least in the same package. Due to the low-level analog output of typical sensors, designing interface electronics that ¿does no harm,¿ i.e. does not impair sensor performance, is quite challenging, especially in today¿s mainstream CMOS technology, whose inherent precision is limited by 1/f noise and component mismatch. However, since most sensors are quite slow compared to transistors, dynamic techniques can often be used to trade speed or bandwidth for higher precision. Examples of such techniques are auto zeroing, chopping, dynamic element matching, switched-capacitor filtering and sigma-delta modulation. This paper describes the use of such dynamic techniques in the design and realization of state-of-the-art smart CMOS sensors for the measurement of temperature, wind velocity and magnetic field.@en