Tobias Werth

Versatile Sensor Front End for Low-Depth Modulation Capacitive Sensors

Low-depth modulation capacitive sensors, i.e. sensors where the capacitance variations caused by a measurand are only a small fraction of the total capacitance, are frequently encountered in measurement problems. Furthermore, also a conductance (e.g. due to parasitic conductive staining) between the sensor electrodes may affect the capacitance evaluation. We have implemented a capacitive sensor interface in a 0.25 mum CMOS process capable of measuring both conductive and capacitive coupling. The sensor interface provides an offset capacitance compensation and an offset conductance compensation such that a low-depth capacitance modulation can be mapped onto the full scale range of an analog to digital converter. Experimental results for a prototype sensor interface with a capacitive slider array are presented.

A chopped Hall sensor with programmable "true power-on" function

This work presents a Hall sensor for camshaft applications including a programmable true power-on switching level effective after the power-up phase. The proposed chopping techniques and self-compensation methods for temperature drifts and technology spreads improve the magnetic offsets from 5-10 mT to below 200 /spl mu/T in a bandwidth of 30 kHz and stabilize the spread of the magnetic switching points from 20% to <2% in a temperature range from -40/spl deg/C to 175/spl deg/C. Internal ADC, DAC and digital signal processing provide an enhanced self-calibration algorithm to adjust the magnetic switching point and to improve the phase error to <0.5/spl deg/. Surface micro-machined cavity fuses offer an end-of-line calibration for the customer with reliable function higher than 195/spl deg/C.

Position Detection in Automotive Application by Adaptive Inter Symbol Interference Removal

Incremental magnetic field sensors are frequently used in automotive applications for crankshaft and camshaft position measurements. Highest possible phase accuracy and disturbance immunity (air gap and temperature variations, noise) are the primary performance requirements for such sensor systems. An analog signal is generated from a magnetic field sensor and the position information is obtained using state of the art peak or zero crossing detection in the analogue or digital domain. While phase jitter of peak or zero crossings can be minimized by optimizing zero crossing and peak detection methods, these techniques cannot take into account variations of peak and zero crossing positions due to air gap variations. A Decision Feedback Equalizer (DFE) was adapted to remove this systematic error. For this purpose a physical model of the measurement environment (magnetic field) was derived and verified by Finite Element simulations (FEM). With simplifications the model delivered an analytical function for magnetic field calculations, which serve the adaptive algorithm for the DFE.

A programmable Hall sensor for camshaft applications

A chopped Hall sensor for camshaft applications is presented which provides a programmable true power-on switching level. The proposed chopping technique and self-compensation methods for temperature drift and technology spread provide a correct output state immediately after power-on even at zero speed of the target wheel. An end-of-line calibration for the customer is implemented using surface micromachined cavity fuses. A novel combination of chopping and enhanced self-calibration algorithm adjusts the magnetic switching point and improves phase accuracy.