A 2 MS/s Full Bandwidth Hall System with Low Offset Enabled by Randomized Spinning

Abstract

In this paper, a Hall plate readout with a randomized four-phase spinning-current scheme is proposed. The goal is to remove the maximum number of offset components, including the offset associated with spike demodulation. The outcome is that only the smallest possible offset remains, corresponding to the residual offset of the Hall plate which cannot be distinguished from the Hall signal. An additional innovation is to operate various offset-reduction loops in spread-spectrum mode, allowing the removal of error components without notching out any in-band signals. The resulting approach delivers a very large notch-free bandwidth while simultaneously reducing the Hall plate residual offset, making it an enabler for high-bandwidth Hall-based current sensors. To demonstrate the proposed techniques, we have realized a mixed-mode experimental circuit, where the analog part is implemented in a custom integrated circuit, and the digital control system in an FPGA is connected to the analog chip. Measurement results feature a Hall readout system with a notch-free bandwidth up to 820 kHz and a 47 μTrms noise floor. The input-referred Hall plate offset, based on statistical measurements on 10 samples from a single wafer, is reduced from 130±22μT to only 23±22μT.

A Benchmark of Integrated Magnetometers and Magnetic Gradiometers

“…Given that silicon Hall magnetic sensors account for the majority (about 80%) of sensors shipped [1], commercial silicon Hall 3D magnetometers [11]- [13] were used as baselines. To illustrate the Hall-effect limits, two recent R&D prototypes were included [14], [15] with optimized signal-conditioning circuits and GaAs Hall plates, respectively. Two recent high-purity graphene Hall transducers were also included: one academic prototype [16], and a commercial one [17].…”

“…As silicon Hall is a mature technology, multiple sensor suppliers or designers approach this limit. For example, in a noise-optimized design [14] using the parameters above, the noise in a 500-Hz bandwidth reaches 1.2 μT, and the noise density 50 nT/…”

A Benchmark of Integrated Magnetometers and Magnetic Gradiometers

“…When the spectrum was not specified, we assumed it was white. For integrated Hall sensors, this is generally the case as the signal is modulated away from the 1/𝑓 noise via the current spinning technique, like in [14].…”

“…For 310 a 4-kΩ Hall plate biased at 3.3V, the above equation yields 311 is a mature technology, multiple sensor 313 suppliers or designers approach this limit. For example, in a 314 noise-optimized design[14] using the parameters above, the 315 noise in a 500-Hz bandwidth reaches 1.2 μT, and the noise 316 density 50 nT/ √ Hz (numerically 20 times less due to the division by √ 500). The GaAs Hall device [15] provides up 318 to 3 extra bits.…”

Editorial for the Special Issue on Electronics for Sensors II

“…In [ 16 ], R. Riem, J. Raman, and P. Rombouts proposed a high bandwidth, low-offset Hall plate read-out system with a randomized four-phase spinning-current scheme. In the manuscript, they demonstrate how it is possible to reduce inessential components to minimize the offset parameter.…”