A high-performance Universal Sensor Interface

This paper describes the typical specifications and features of a low-cost and high-performance Universal Sensor Interface (USI). This device can provide accurate and reliable interfacing for capacitive sensors, platinum resistors, thermistors, resistive bridges, thermocouples, thermopiles, conductivity sensors and pH sensors. The interface converts the sensing-element signal into a period modulated signal (time interval), which is a microcontroller- and DSP-compatible signal. Optionally, the interface can be controlled via an SPI bus. An auxiliary temperature measurement is performed using a resistive temperature sensor. This feature enables compensation for temperature effect. Experimental results show that the interface has a resolution and linearity up to 14.8 bits and 13.5 bits with a measurement time of 100 ms.