A UNIVERSAL TRANSDUCER INTERFACE FOR CAPACITIVE AND RESISTIVE SENSOR ELEMENTS

This paper presents a new universal transducer interface. This interfa ce, which is read out by a microcontroller, services the following sen sor elements: capacitors, platinum resistors, thermistors, resistive b ridges and potentiometers. The A/D conversion is based on a first-orde r oscillator A combination of classical and some new measurement techn iques has been applied on a single chip to obtain high accuracy, good long-term stability and a reduction of the effects of interference and parasitic elements. The circuit has been fabricated in a 0.7 mu m CMO S process. The main test results are: an accuracy of 10-15 bits and a resolution up to 16 bits while the measurement time is in the range 1- 100ms. These results hold over the temperature range -20 degrees-C to 80 degrees-C. Calibration of the electronic part is not required. The number of external components has been kept to a minimum.