Christian Schott

A CMOS Single-Chip Electronic Compass with Microcontroller

A CMOS single-chip electronic compass with a 16b DSP for heading calculation is presented. A Hall-based 3-axis magnetic-field sensor and analog amplifiers, with a gain of up to 20,000, drive a 12b ADC. A 0.35mum low-voltage CMOS process is used with an added metal layer working as a magnetic-field concentrator with a gain of about 6 to 10. The chip works with a 2.2 to 3.6V supply and draws 5mA in normal mode. The heading resolution is better than 0.5deg and the accuracy is better than plusmn2deg

Electronic compass sensor

In this paper, we describe a new two respective three axis integrated IMC Hall-ASIC that can be used as a single chip electronic compass and applied in portable low cost electronic equipment like wrist watches and mobile phones. The electronic compass chip consists of ring shaped integrated ferromagnetic concentrators (IMC), a CMOS integrated circuit and an excitation coil manufactured by direct bonding onto the chip surface. The IMC Hall ASIC measures the two in-plane magnetic field components Bx and By and the vertical component Bz of the Earths magnetic field. The IMC Hall sensor exhibits an excellent sensitivity of 8000 V/T for the X and Y axis which yields an in-plane heading accuracy of +/-1/spl deg/, whereas the field in the Z-axis is measured with a lower sensitivity of 800 V/T. The high sensitivity characteristics are obtained by integrating magnetic flux concentrators directly on the Hall-ASIC, which amplifies the Earths magnetic field by a factor of 10. Furthermore, the compass sensors provides a low energy method to eliminate the perming effect (remnant field effect after subjecting to strong magnetic fields).

A Vertical Hall Device in CMOS High-Voltage Technology

In this paper we demonstrate for the first time, how vertical Hall devices manufactured in CMOS technology attain sensitivities comparable to those of conventional silicon plate-shape devices without any additional etching step. This was achieved by taking advantage of the low doping levels of a high-voltage technology. An additional unconventional doping reduction method can further improve the sensitivity. The current related sensitivity of the presented devices varies from 18 V/AT up to 127 V/AT for different sensor geometry and doping concentrations. The linearity error is less than 0.04% for magnetic fields up to 2T.

High accuracy analog Hall probe

The Hall probe we developed is a miniaturized analog system, consisting of two silicon vertical Hall devices, current stabilizers, amplifiers and error-correcting circuits. The output signal is 1 V/T, with an error less than 10/sup -4/ in the ranges /spl plusmn/2 T, 15/spl deg/C to 35/spl deg/C, and DC to 10 kHz. The probe features high long-term stability, low offset drift and low noise.

Smart CMOS sensors with integrated magnetic concentrators

The combination of integrated magnetic concentrators (IMC) and modern CMOS Hall sensor technology extends the frontiers of magnetic sensing to new dimensions. Single-axis sensors are turned into multi-axis sensors while signal quality and resolution are enhanced by up to one order of magnitude. Integrated Magnetic Concentrators have a deep impact on sensor system design. On one hand, the material properties of the added magnetic layer and the tolerances arising from its deposition and structuring have to be taken into account. On the other hand multi-axis sensors offer the possibility to work with ratios of magnetic field components rather than with a single field component. This results in ageing and drift effects of sensor and magnet being virtually eliminated

CMOS three axis Hall sensor and joystick application

We present for the first time a three-axis CMOS Hall sensor based on integrated magnetic concentrator technology (IMC). The sensor measures the two in-plane magnetic field components Bx and By and the vertical component Bz and generates three output voltages proportional to them. The sensing core consists of four Hall elements arranged at 90/spl deg/ under the edge of a ferromagnetic disk (IMC), which is attached to the silicon die. By subtracting the Hall voltages of two opposite Hall elements a voltage proportional to the in-plane components is generated and by adding them a voltage proportional to the perpendicular component. In such a way a planar structure is used to implement a three-axis sensor device. The sensor further contains current sources, dynamic offset compensation and signal amplification and conditioning. The sensor aims for applications where two translatory or rotational movements have to be measured independently and precisely over a large temperature range. Examples are joysticks, car mirror sensors and other control devices.

A Fully Integrated Analog Compensation for the Piezo-Hall Effect in a CMOS Single-Chip Hall Sensor Microsystem

A magnetic sensor microsystem with Hall plates, temperature sensor, and stress sensor designed for the purpose of temperature-dependent piezo-Hall effect compensation has been implemented in 0.35μm CMOS technology. The sensor microsystem as well as the compensation method is entirely realized in integrated analog circuitry. A dedicated stress sensor delivers a signal proportional to the sum of in-plane normal stresses. At the systems level, the analog circuit compensates the stress-related drift of the magnetic sensitivity by adding a current proportional to the stress sensor signal on top of the Hall plate supply current. After a three-temperature calibration of a sensor molded in a SOIC-8 package extending from -40 °C to +125 °C, the residual thermal drift of the magnetic sensitivity was reduced to <;0.5%. The stress-related drift due to a humidity change from humid to dry was reduced to <;0.6% for samples packaged in SOIC-8 and single-in-line molded packages.

High volume production of magnetic sensors for the automotive market

Magnetic sensors, like other electronic components used in automobiles need to be manufactured on-time in high volume at very high quality. Those requirements can only be fulfilled by a very specific process going from a six-sigma design over a sample-based qualification according to AEC-Q100 to the reliability screening tests run on full production. In this paper we discuss the motivations and principles of such an automotive quality system and then illustrate them by the example of a standard magnetic angular position sensor.

Modern CMOS Hall Sensors with Integrated Magnetic Concentrators

Combining modern CMOS Hall sensors with integrated magnetic concentrators dramatically enhances magnetic field measurement performance. A first key feature is that one, two, or all three magnetic field components can be measured in a small spot. On-chip digital signal processing allows for the evaluation of the flux density vector direction instead of merely the flux density strength. By this principle very robust and thermally insensitive contact-less angular and linear position sensors can be made. The second key feature is the passive magnetic flux amplification of the integrated concentrator by up to one order of magnitude. This feature is particularly interesting for the measurement of low flux density as for example around a current carrying conductor. The combination of low-field amplification and multi-axis capability allows even to address applications like the electronic compass, which have up to now been considered as far too demanding for Hall sensors.

A bridge-type resistive temperature sensor in CMOS technology with low stress sensitivity

CMOS resistive and bipolar temperature sensors are sensitive to mechanical stress via the piezoresistance and piezojunction effects. In this paper we present a CMOS compatible temperature sensor with differential output and low stress sensitivity. The sensor is based on 16 appropriately arranged p-well and p-poly resistors combined in a Wheatstone bridge in such a way as to provide isotropic piezoresistance for the sum of in-plane normal stress and to compensate the junction field effect. At room temperature the sensitivities with respect to temperature and stress were found to be 3.9mV/K and -29 uV /MPa, respectively. Hence, the sensor experiences a stress-related error as small as -0.0074K/MPa. In contrast to conventional bipolar approaches our sensor does not require any circuitry. Moreover, it can be placed easily at the desired location on the chip thanks to its small size of 61um × 61 um.