Universal Asynchronous Sensor Interfaces

Sensor interfaces should provide an output signal that can be read out by a microcontroller. This paper shows, that besides digital output signals also time-modulated signals are suited to be read out by microcontrollers. It is shown, that the attractive features of time-modulated signals concern the simplicity of the circuits and the flexibility of the signal processing. It is shown that precision interface chips can be implemented with low-cost CMOS technology. To make the interface chips universal, specific physical problems for typical applications and measurements have been taken into account. Interface chips in which dedicated measurement techniques have been applied, including autocalibration, two-port measurement and advanced chopping, can be very users friendly. Moreover, these techniques enable selective detection of the measurand with a high immunity for parasitic effects of the sensing elements, and for the effects of the connecting wires. As case studies, interface systems have been presented for capacitive sensors, resistive-bridge sensors.