Smart sensor design: The art of compensation and cancellation

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.