Fully integrated sensor electronics for inductive proximity switches operating up to 250 °C

In this paper we present an integrated circuit for inductive proximity switches which requires very few external components and can operate under ambient temperatures up to 250 °C. The sensor system is realized in the Fraunhofer IMS H035 technology which was specifically developed for high temperature operation. The core of the circuit is built of an oscillator which is equipped with a peak detector and readout electronics for threshold detection, references and voltage regulators to provide the necessary internal voltages as well as extensive trimming capabilities to compensate for temperature effects. The circuit can be operated from a single dc-voltage supply from 12 to 35 Volts. Calibration data can be stored in an internal EEPROM. Switching distance and hysteresis are programmable for adapting the circuit to a wide range of different detector coils and sensor geometries. Two output signals are provided that can be independently set to function as push/pull or single ended switches with programmable polarity. The only external components required are blocking capacitors for supply voltage stabilization and the LC resonator circuitry. Reverse polarity protection and special high temperature ESD and clamping structures are also fully integrated on the silicon die.