Hall Plate Biasing Circuit for Linearity and Cross-Sensitivity
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Solution Overview
Problem
Existing Hall sensor technologies face challenges in maintaining constant plate thickness and linearity due to temperature and piezoresistive stress effects, leading to cross-sensitivity issues and non-linear magnetic field measurements.
Innovation Solution
A circuit and method for biasing plate-shaped sensor elements using a combination of current sources and a negative feedback loop to stabilize the common mode voltage, ensuring minimal loading and reduced influence of contact resistance mismatches, while allowing the plate thickness to remain constant near the center, thereby improving linearity and reducing cross-sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current biasing is used to supply precise current through the Hall plate, then the applied current is precisely known, but the voltage over the plate varies with temperature and piezoresistive stress effects causing non-linear measurements
Solution Approach 1:
The patent implements a feedback circuit that continuously monitors the voltage between sense contacts and adjusts the current source accordingly. This feedback mechanism compensates for temperature and piezoresistive stress effects by dynamically adjusting the bias current to maintain linear measurement characteristics across varying environmental conditions.
Solution Approach 2:
The patent changes the operating parameters of the Hall plate by applying reverse bias voltages to the isolation junctions. This modifies the depletion region widths and electrical characteristics of the plate, enabling compensation for temperature and stress-induced non-linearities while maintaining precise current control.
2Reliability
If reverse-biased PN-junctions are used to electrically isolate the Hall element from the substrate, then electrical isolation is achieved, but the depletion regions cause non-uniform plate thickness leading to sensitivity variations
Solution Approach 1:
The patent applies different reverse bias voltages to different isolation junctions around the Hall plate. By locally adjusting the depletion region widths at specific junctions, the patent compensates for non-uniform plate thickness effects and maintains uniform sensitivity across the active area of the Hall element.
3Ease of manufacture
If the Hall element is co-integrated with readout circuitry in CMOS technology, then integration is achieved, but the Hall element requires electrical isolation from the substrate which complicates the design
Solution Approach 1:
The patent merges the isolation function with the readout circuitry by integrating the biasing and compensation circuits directly with the Hall element in the CMOS substrate. This combined approach achieves electrical isolation while maintaining compact integration, eliminating the need for separate isolation structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves improved linearity and reduced cross-sensitivity to environmental factors, enhancing the accuracy of magnetic field measurements by maintaining a stable plate thickness and minimizing the impact of temperature and stress variations.
Implementation Method 1
A current has to flow through the device. A bias current I is supplied via two of the contacts
Implementation Method 2
a negative feedback loop for controlling the second source based on a comparison between a value representative for a common mode voltage of the voltages of the sense nodes and a predefined reference voltage
Implementation Method 3
The plate-shaped sensor element is embedded into a substrate or well such that it can be isolated from the substrate or well by means of a first PN-junction
Implementation Method 4
Hall sensors are magnetic sensors based on the Hall effect... If a current I is applied to the current contacts A, C, and if an out-of-plane magnetic field Bz is applied to the device, a Hall voltage VH proportional to the applied magnetic field Bz will appear between the sense contacts B, D
Implementation Method 5
the voltage over the plate depends on the total resistivity of the plate... the voltages also vary in the X-direction of FIG. 2. Because these effects modulate the thickness of the plate, they affect the sensitivity and the linearity of the magnetic sensor
Data Source
AI summary
Circuit and method for biasing a plate-shaped sensor element (2) made of doped semiconductor material and having a first resp. second excitation contact (C, A) connected to a first resp. second excitation node (Cn, An), and a first resp. second sense contact (B, D) connected to a first resp. second sense node (Bn, Dn). The plate-shaped sensor element is electrically isolated from a substrate or well (5) by means of a first PN-junction. The method comprises: a) applying to the first excitation node (Cn) a predefined first current (Iex) generated by a first current source (11); b) applying to the second excitation node (An) a second current (I′ex) generated by a controllable second source (12); c) controlling the second source (12) by means of a negative feedback loop based on a comparison between a value representative for a common mode voltage (Vcm) of the voltages (VB, VD) of the sense nodes (Bn, Dn) and a predefined reference voltage (Vref), such that the common mode voltage (Vcm) is substantially equal to the reference voltage (Vref).