CVH Sensor DC Offset Removal via Gilbert Cell Filter

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Solution Overview

Problem

Circular Vertical Hall (CVH) sensing elements often produce output signals with significant DC offsets, which can lead to errors and inaccuracies in signal processing, such as signal clipping during amplification or other processing steps.

Innovation Solution

A magnetic field sensor is designed with a circular vertical Hall sensing element and a filter, specifically a Gilbert cell, which is AC-coupled to remove the DC component from the analog signal produced by the CVH sensing element, followed by an analog-to-digital conversion to generate a digital signal representing the magnetic field strength and angle.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a CVH sensing element is used to detect magnetic field, then magnetic field sensing capability is improved, but DC offset in output signal causes errors and inaccuracies

Engineering Contradiction:

Improvemagnetic field detection accuracyVSAvoidsignal processing accuracy

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent extracts and removes the DC offset component from the CVH sensing element output signal using a high-pass filter. This separates the unwanted DC component from the useful AC signal containing magnetic field information, thereby eliminating the source of measurement errors while preserving the accurate magnetic field detection capability.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a high-pass filter as an intermediary component between the CVH sensing element and the signal processing stage. This filter acts as a mediator that selectively passes the AC signal components containing magnetic field information while blocking the DC offset, thus improving both measurement precision and processing reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If DC offset is large in CVH output signal, then signal processing becomes simpler, but signal clipping occurs during amplification

Engineering Contradiction:

Improvesignal processing complexityVSAvoidsignal integrity

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent applies preliminary action by removing the DC offset from the CVH sensing element output signal before the signal enters the amplification and processing stages. This pre-processing step prevents subsequent signal clipping and distortion, ensuring signal integrity throughout the processing chain while maintaining manageable processing complexity.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If DC offset removal filter is added to CVH sensor, then signal accuracy is improved, but device complexity increases

Engineering Contradiction:

Improveoutput signal accuracyVSAvoidcircuit structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

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 effectively removes DC offsets from the CVH sensing element's output, reducing errors and ensuring accurate processing of the magnetic field signals, thereby enhancing the precision of magnetic field detection and measurement.

Implementation Method 1

One type of current sensor uses a Hall effect magnetic field sensing element in proximity to a current-carrying conductor.

Methodology Applied

Scientific EffectHall effect: Hall Effect

Implementation Method 2

a filter coupled to the CVH output stage to receive the analog signal, the filter configured to remove a DC component from the analog signal to produce a filtered signal

Methodology Applied

Scientific EffectDC offset removal: Filter (electronic)

Data Source

PatentUS10495701B2Circular vertical hall (CVH) sensing element with DC offset removal

Publication Date: 2019.12.03 ALLEGRO MICROSYSTEMS LLC

AI summary

A magnetic field sensor includes a semiconductor substrate, a circular vertical Hall (CVH) sensing element comprising a plurality of Hall elements arranged over an implant region in a semiconductor substrate, adjacent ones of the plurality of vertical Hall element at predetermined angles from each other. A CVH output stage may comprise one or more of drive circuits to drive the plurality of vertical Hall elements and produce an analog signal, and a filter coupled to the CVH output stage to receive the analog signal. The filter may be configured to remove a DC component from the analog signal to produce a filtered signal. An analog-to-digital converter may be coupled to receive the filtered signal and produce a digital signal. A processor stage may be coupled to receive the filtered signal and operable to compute an estimated angle of the external magnetic field.