Serge Reymond

Circular Hall Transducer for Angular Position Sensing

We developed a new integrated magnetic sensor based on the Hall effect, suitable for contactless 360deg absolute angle encoding. The sensing device consists of a narrow n-well ring with a chain of 64 contacts equally distributed along the ring. It is connected to on-chip biasing and signal conditioning circuits that provides the magnitude and the phase of the in-plane component of the magnetic field. In a homogenous magnetic field, the transducer angular resolution is 0.01deg in the 1 kHz frequency bandwidth and the absolute accuracy is about 1deg and 0.1deg without and with output offset calibration, respectively.

True 2D CMOS integrated Hall sensor

We have designed and realized a new integrated Hall structure that converts the magnetic field vector in the chip plane, into an ac signal, whose amplitude and phase correspond to the magnitude and direction of the field. It is the first Hall sensor that provides the field angle without the need of computing an arctan function. The Hall structure is formed by a n-well ring with a large number of contacts equally distributed along the ring, like a circular railroad track. Each contact is connected to the control electronics through switches. The measurement consists in activating a small portion of the ring at the time, forming a vertical Hall probe and uses the switches to make this portion circulate. The measurement sequence suppresses the zero-field offset and the 1/f noise. At 100 Hz, the resolution is 14 muT and 0.008deg. We propose a measurement scheme to further reduce the offset, and remove the need for calibration.

Ultra low-power angular position sensor for high-speed portable applications

We present a technique for contactless angular position sensing that allows low power consumption while keeping dynamic properties comparable to existing sensors. The technique essentially consists in combining a recently developed sensing element, the so-called Circular Vertical Hall Device, with a simple and robust signal treatment based on phase detection. Because of its low startup time, this circuit is specially suited for pulsed mode operation, which enables to further decrease the power consumption. More generally, the absence of complex digital signal treatment makes this technique a natural method for measuring the magnetic field direction and therefore for designing an angular position sensor using Hall probes.

Purely CMOS angular position sensor based on a new hall microchip

This paper presents a new technique to sense the direction of the magnetic field, enabling a new generation of contactless 360deg absolute angle encoders. The sensor consists of a microchip that contains a special ring-shaped Hall element. It is the first sensor that gives the angle value without the need of computing an arctan function. In addition, we demonstrate that this system is compatible with a self calibration method. Measurements were performed with the microchip operating inside a hollow permanent magnet and an accuracy of 0.1deg was obtained without calibration.

On performance of series connected CMOS vertical hall devices

Series connected (stacked) CMOS vertical Hall devices were analyzed on the basis of performance of a single five contacts device biased at different common mode voltages with respect to the substrate. The uneven influence of junction field effect on residual offset voltage, sensitivity and residual offset equivalent magnetic field was studied. It was shown that though junction field effect leads to some increase in offset voltage for devices with higher common mode, this effect can be minimized through suitable biasing.

A Completely Scalable Lumped-Circuit Model for Horizontal and Vertical HALL Devices

A completely scalable lumped-circuit model for horizontal and vertical HALL devices is presented therein that can be efficiently implemented in SPICE-like EDA simulators. The model has been employed for the quantitative analysis of: a) geometrical, b) temperature, and c) field-dependent mobility effects, as well as for d) the dynamic response and e) the noise behavior of several HALL sensors. A series of experimental data is presented along with simulation results.

Offset Compensation Based on Distributed Hall Cell Architecture

A new offset reduction strategy for CMOS Hall devices is proposed. The novelty is to fragment the Hall device into multiple Hall blocks, distributed over the silicon area and easy to interconnect. The suitable number of Hall blocks and the bias current level in each block can be adjusted according to the requirements in terms of offset, offset drift and signal to noise ratio. A chip was fabricated in 0.35 μm CMOS standard technology to demonstrate the potential of this architecture. The chip shows promising results, and in particular, a very low offset drift was observed at the front-end output stage (of the order of 10 nT/°C).