Dirk Hammerschmidt

Ultra low-power monolithically integrated, capacitive pressure sensor for tire pressure monitoring

Tire pressure monitoring systems (TPMS) are gaining importance due to improved security standards in the automotive industry. In active systems, the power consumption of the system is of utmost importance for a required lifetime of more than 10 years. The presented integrated circuit comprises high resolution pressure, temperature and voltage monitoring, low-power oscillators, a specialized DSP with RAM/ROM and an EEPROM to store calibration data. The continuously running low-power oscillator for internal wake-up timing is operated with 30 nA. Due to the extremely low-power consumption of all circuit blocks, pressure measurements can be carried out in short intervals (0.5 s). This enables the implementation of a new intelligent dynamic wake-up algorithm to optimize the power-intensive HF-transmission intervals under different driving situations. Thus additional rotation detectors are not needed any more. The charge consumption without HF-transmission results in 48 mAh in 10 years.

Integrated Gigant Magnetic Resistance based Angle Sensor

An integrated GMR (giant-magnetic-resistance) sensor is presented for 360deg angular measurements of rotating magnetic fields in automotive applications. The spin-valve GMR-layers are directly applied to a standard semiconductor 0.22 mum CMOS process by vertical integration of the sensor-bridges atop of active circuitry. The entire integrated angle-sensor comprises 2 orthogonal magnetized GMR-bridges for sine and cosine signal measurements, and the subsequent signal conditioning circuitry. The entire angular sensor is designed to work in harsh automotive environment in a temperature range of -40degC to 150degC. The strength for best precision covers a wide range from 20 to 50 mT. The resulting angular information itself can be obtained by SPI-readout and calculating the arc-trigonometric function of the bridge signals with a resolution of >13 bit in an auxiliary microcontroller. After individual calibration to compensate for production spread an accuracy of typical 0.5deg is achieved.

Versatile programmable integrated interface for robust capacitive sensors

SummaryDue to the unparalleled simplicity of its sensor elements, its versatility due to a plurality of applicable materials and the availability of small and fairly low cost monolithic sensor interfaces, the acceptance of capacitive technology has constantly increased during the last years. This work addresses the design of a versatile sensor interface for capacitive sensors usable for automotive and industrial measurement problems. The interface is implemented in a 0.25 µm CMOS technology and provides mechanisms in order to cope with front end parasitic effects and external electromagnetic compatibility disturbers. The presented interface is used to evaluate the coupling capacitances of a spatial filtering sensor for flow velocity determination of liquid hydrogen.ZusammenfassungDiese Arbeit beschreibt die Entwicklung einer vielseitig anwendbaren Auswerteeinheit für kapazitive Sensoren, die in industriellen und automotiven Messaufgaben eingesetzt werden kann. Die Schaltung ist in einer 0,25-μm-CMOS-Technologie implementiert. Das Systemkonzept sieht entsprechende Mechanismen vor, um den in rauen Umgebungsbedingungen vorhandenen Parasitäreffekten sowie möglichen externen EMV-Störungen entgegenzuwirken. Die Auswerteeinheit wird in einem Anwendungsbeispiel zur Bestimmung der Durchflussgeschwindigkeit von flüssigem Wasserstoff mittels Ortsfrequenzfilterung verwendet.

Integrated Giant Magneto Resistors — a new Sensor Technology for Automotive Applications

The paper will give an introduction to the principle of the giant magneto resistive — GMR — effect and the silicon system integration of GMR sensors. The two main applications of a GMR are as a magnetic field strength sensor and as an angular field direction sensor. They will be discussed under consideration of automotive requirements.

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.

Giant Magneto Resistors - Sensor Technology and Automotive Applications

The paper will give an introduction to the principle of the giant magneto resistive - GMR - effect and the silicon system integration of GMR sensors. The two main applications of a GMR as a magnetic field strength sensor and as an angular field direction sensor will be discussed under consideration of automotive requirements. The typical applications of a magnetic field strength GMR sensor in incremental position and speed sensing and those of GMR angular field sensors in position sensing will be summarized. Finally advantages of GMR in those applications will be discussed and conclusions on the use of GMR in automotive sensing will be drawn.

Automotive Sensors & Sensor Interfaces

The increasing legal requirements for safety, emission reduction, fuel economy and onboard diagnosis systems push the market for more innovative solutions with rapidly increasing complexity. Hence, the embedded systems that will have to control the automobiles have been developed at such an extent that they are now equivalent in scale and complexity to the most sophisticated avionics systems. This paper will demonstrate the key elements to provide a powerful, scalable and configurable solution that offers a migration pass to evolution an even revolution of automotive Sensors and Sensor interfaces. The document will explore different architectures and partitioning. Sensor technologies such as magnetic field sensors based on the hall effect as well as bulk and surface silicon micro machined sensors will be mapped to automotive applications by examples. Functions such as self-test, self-calibration and self-repair will be developed. Possible migration to lower voltage (5V to 3,3V) will be investigated. In this context the document will also propose sensors interfaces to ease the signal conditioning inside the ECU. An insight of sensor busses will be performed to provide a picture of sensor networks.

Compensation of Angular Errors Using Decision Feedback Equalizer Approach

Speed and position measurements of rotating shafts are very important in the field of mechanical engineering. In automotive applications, magnetic field sensors for such measurements (camshaft, crankshaft, anti-lock braking system, windshield wiper, etc.) have the largest market share of all sensor types. Camshaft applications are challenging due to their requirements on high angular accuracy under harsh environmental conditions. Due to mounting and packaging tolerances, the magnetic field at the sensors position varies, resulting in angular measurement errors for sensor concepts in use today. Mounting and packaging tolerances cannot be avoided; however, they can be compensated by a new filter structure which is described in this paper. The decision feedback equalizer (DFE) - known from digital communication - was analyzed and modified for the use in angular measurement applications. A new filter structure, using data prediction and an adaptive algorithm based on a physical model, is proposed. This filter calculates and compensates angular errors caused by mounting and packaging tolerances.

Phase demodulation of magnetic GMR signal for virtual sensing applications by using hilbert transform

GMR (Giant MagnetoResistance) sensors, which are used in conjunction with magnetic encoders (magnetic pole wheels), have a huge number of applications in automotive and machine industry, where they are used to compute the rotational speed of rotating parts like wheels and shafts. In this paper, we present an analytical model of magnetic pole wheel signal as it is sensed by a GMR sensor. Experimental measurements are performed to check the validity of the mathematical model. Furthermore, we present a novel digital signal processing technique, which incorporates the Hilbert transformer to phase demodulate this GMR signals to compute high resolution instantaneous position and speed information. A frequency domain analysis is then deployed to analyze the signal for any low frequency vibrations present in the rotating part.

New Modeling & Evaluation Approach for Capacitive Occupant Detection in Vehicles

Capacitive occupant detection is a contactless sensing technique which helps to improve safety standards in vehicles. This paper details the problem of relating measured sensor signals with physical model parameters. An innovative modeling approach is discussed, which takes into account different current pathways including also the influence of human passengers. Furthermore, a new electrode area variation method is introduced which allows to extract wanted model parameters. Finite Element Simulation shows that the proposed electrode area variation method is applicable for capacitive occupant detection sensors.