Mario Motz

Compensation of the Piezo-Hall Effect in Integrated Hall Sensors on (100)-Si

Silicon Hall sensors are known to suffer from a long-term drift in the magnetic sensitivity between 1% and 4%, depending on the degree of moisture in the mold compound of the package. This drift is mainly caused by changes of mechanical stress exerted by the plastic package onto the die. We present a system, which continuously measures the relevant stress components, estimates the sensitivity drift, and corrects for it digitally. An individual precalibration versus temperature is necessary to achieve the required level of accuracy. Results from laboratory characterization with pressure cells and lifetime drift during qualification runs show that this system can keep the drift of magnetic sensitivity well below 1%.

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.

An Integrated Hall Sensor Platform Design for Position, Angle and Current Sensing

A new platform design of a Hall sensor uses digital signal processing and digital 3rd order temperature compensation. The improved architecture of the front-end achieves low noise of <2 muT in a bandwidth of 400 Hz by using a 3rd-order multibit continuous-time DeltaSigma-ADC. By chopping the first stage of this ADC a low magnetic offset of <50 muT is realized in a typical automotive operating temperature range from -50 to 150degC. A novel circuit technique for a stress sensor is used to compensate stress and aging effects in the Hall sensor. All required digital calculations are done at low power and area with a new intelligent state machine, which also provides various digital interface protocols.

A miniature digital current sensor with differential Hall probes using enhanced chopping techniques and mechanical stress compensation

A 10kHz bandwidth 50Amax current sensor using a Hall effect gradiometer without magnetic core provides 80kHz update rate with a digital interface. Very low un-calibrated offset of 30mA (1σ) and after calibration typical 10mA over temperature is accomplished by a chopped multi-bit feedback continuous-time 3rd order ΔΣ-ADC. This also realizes low noise of 13mArms in 1kHz signal bandwidth. The ADC uses enhanced chopping techniques and additional digital feedback loops to avoid chopper ripple. New analog and digital stress-compensation circuits with lateral and vertical n-doped resistors achieve lifetime gain drifts below 1% and temperature compensation. Auto-zeroing ping-pong comparators offer a fast over-current detection of 1...2μs on a dedicated output pin. The monolithic integrated sensor chip and the 4kV galvanic isolated current rail fit into a very small 7×7×1mm3 package.

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.

Drift of magnetic sensitivity of smart Hall sensors due to moisture absorbed by the IC-package [automotive applications]

For automotive applications like cam-shaft, crank-shaft, throttle valve or accelerator pedal position sensing, Hall probes are integrated together with biasing and complex signal processing circuits into tiny plastic packages. Instabilities of magnetic switching points and magnetic sensitivity have been observed for some time. We show by way of experiments that the main contribution to this sensitivity drift originates from moisture absorption by the mold compound of the plastic package which changes the mechanical stress on the die. The mechanical stress affects the Hall factor of the Hall probe (piezo-Hall effect) and the current through the Hall probe (piezo-resistance effect) which finally leads to a drift of the overall magnetic sensitivity.

5.8 A digitally assisted single-point-calibration CMOS bandgap voltage reference with a 3σ inaccuracy of ±0.08% for fuel-gauge applications

Accurate voltage references are key building blocks for almost all electronic systems. Specifically, fuel gauge applications benefit from very high precision references to allow for extremely precise measurement of battery voltage and current in order to provide an accurate measurement of the state of charge of the battery.

An Integrated Magnetic Sensor with Two Continuous-Time /spl Delta//spl Sigma/-Converters and Stress Compensation Capability

A linear 4kHz Hall sensor in 0.6mum BiCMOS has digital 3rd-order temperature compensation, a DR of 90dB and an offset of 50muT. It uses a chopped 3rd-order multibit CT-DeltaSigma ADC including an up/down counter loop and bandgap-based compensation for stability and accuracy. Digital compensation of sensitivity drift caused by package-induced stress is provided

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.

Electrical Compensation of Mechanical Stress Drift in Precision Analog Circuits

Mechanical stress has a notable effect on the parameters of most micro-electronic devices. This leads to inaccuracies and drifts, which are relevant for precision analog circuits. In contrast to built-in stress during wafer manufacturing processes, mechanical stress caused by packaging process shows a marked short and long term drift mainly due to moisture absorption. For economic plastic encapsulated packages with high reliability for automotive applications it seems impossible to avoid the drift of mechanical stress. A cost efficient way to tackle this problem is to measure the mechanical stress on-chip and to compensate for its effects by way of an electronic circuit. The paper explains the main concepts and challenges of these mechanical stress compensation circuits. It shows which classes of circuits are suited for this technique, which are the costs and benefits.