Noise-Shaped Switching Circuits for Offset and 1/f Noise Reduction

Solution Overview

Problem

Conventional chopping methods for mitigating offsets and 1/f noise in electronic circuits, such as Hall sensor circuits, introduce undesirable tones and require high sampling frequencies, which can be unacceptable in certain applications and add noise when attempting to cancel remaining offsets.

Innovation Solution

Implementing noise shaped spinning using uncorrelated digital Delta-Sigma modulators to control switching circuits in a non-ordered time sequence, spreading the energy of offsets and 1/f noise to a frequency range higher than and out of the desired signal band, while using a digital signal processor to measure and cancel residual offsets and noise without adding additional noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional chopping methods are used to mitigate offsets and 1/f noise, then offsets and noise are modulated to higher frequencies, but undesirable tones are introduced and high sampling frequencies are required

Engineering Contradiction:

Improveoffset and noise reductionVSAvoidundesirable tones

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent employs periodic switching of current direction through the Hall sensor at a defined chopping frequency to modulate offsets and 1/f noise to higher frequencies, while using synchronous demodulation to recover the desired signal at the original frequency

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements feedback by measuring the output signal, demodulating it to extract the desired component, and using this information to cancel offsets and noise through controlled switching, thereby continuously improving measurement accuracy

Inventive Principle:

Principle #23Feedback

2Measurement precision

If conventional chopping methods are used to mitigate offsets and 1/f noise, then offsets and noise are modulated to higher frequencies, but high sampling frequencies are required which add noise when attempting to cancel remaining offsets

Engineering Contradiction:

Improveoffset and noise reductionVSAvoidsystem noise

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent implements feedback by measuring the output signal, demodulating it to extract the desired component, and using this information to cancel offsets and noise through controlled switching, thereby continuously improving measurement accuracy

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces high-frequency physical sampling with digital signal processing techniques, including synchronous demodulation and digital filtering, to recover and process the signal at lower effective frequencies, thereby reducing the need for high sampling rates and associated noise

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If conventional chopping methods are used to mitigate offsets and 1/f noise, then offsets and noise are modulated to higher frequencies, but the spurious-free dynamic range is reduced

Engineering Contradiction:

Improveoffset and noise reductionVSAvoidspurious-free dynamic range

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent replaces high-frequency physical sampling with digital signal processing techniques, including synchronous demodulation and digital filtering, to recover and process the signal at lower effective frequencies, thereby reducing the need for high sampling rates and associated noise

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces synchronous demodulation as an intermediary process that separates the desired signal from chopped offsets and noise by using a reference signal at the chopping frequency, allowing selective recovery of the useful signal while rejecting modulated noise components

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

This approach effectively reduces offsets and 1/f noise energy without introducing tones, achieving a similar level of energy reduction with less attenuation and preserving the spurious-free dynamic range, allowing for efficient cancellation of residual noise without increasing system noise.

Implementation Method 1

a Hall plate (104) that, in response to an input forced into the Hall plate, produces a signal having a desired frequency band and offsets and 1/f noise having energy

Methodology Applied

Scientific EffectHall effect: Hall Effect

Data Source

PatentUS10690730B2Apparatus and method for reducing offsets and 1/f noise

Publication Date: 2020.06.23 CIRRUS LOGIC INC

AI summary

Switching circuits controllable to force an input into a circuit and to sense a responsively produced output in multiple ways to produce different combinations of positive and negative polarities of a desired signal and of sources of offsets and 1/f noise. The switching circuits are controlled in a non-ordered time sequence of different combinations of positive and negative polarities of the sources of the offsets and 1/f noise that spreads their energy to a frequency range above the desired signal frequency band. The non-ordered time sequence leaves the polarity of the desired signal unchanged. Uncorrelated delta-sigma modulators may generate the control signal. A DSP processes a resulting spectrum of a digital domain version of the sensed output to measure residual offsets and 1/f noise and adds to an input present at the DSMs a signal equal in magnitude and opposite in sign to the measured residual offsets and 1/f noise.