Differential Charge Amplifier Noise Reduction

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Solution Overview

Problem

Signal conditioning circuits face challenges in maintaining a high signal-to-noise ratio when measuring pico coulomb charges in noisy, elevated-temperature, and corrosive environments due to common mode noise picked up by cables, which is exacerbated by long cable lengths and sensitivity of sensors.

Innovation Solution

A low noise differential charge amplifier circuit utilizing a twisted or untwisted two pair cable with a grounded shield, featuring auto offset correction circuits to reduce noise interference, where one pair is connected to a sensor and the other to a sensor equivalent impedance circuit, and both pairs are shielded to minimize common mode noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If long cable connections are used between sensors and signal conditioning circuits, then the quality of air control can be maintained through comprehensive sensing, but the signal to noise ratio deteriorates due to electrical interference pickup

Engineering Contradiction:

Improvesensing coverageVSAvoidsignal to noise ratio

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent divides the signal transmission system into differential pairs and uses a differential amplifier to process the signals. By segmenting the noise rejection function into the differential amplification stage, the system maintains long cable connections for comprehensive sensing while rejecting common-mode noise to preserve signal-to-noise ratio.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent converts the harmful common-mode noise picked up by long cables into a beneficial signal rejection opportunity. By using differential amplification, the common-mode noise that couples equally onto both lines is rejected, transforming the harmful interference into a demonstrable advantage of the differential architecture.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Measurement precision

If high sensitivity sensors are used to detect pico coulomb charges, then measurement capability is improved, but common mode noise pickup is exacerbated

Engineering Contradiction:

Improvecharge detection sensitivityVSAvoidcommon mode noise

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent segments the signal processing into differential channels that independently handle the sensitive charge detection while rejecting common-mode interference. The differential amplifier architecture separates the useful differential signal from the harmful common-mode noise, enabling high sensitivity measurement despite the presence of noise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent transforms the harmful common-mode noise into a beneficial rejection target. By designing the system to detect differential signals, the common-mode noise that affects both lines equally becomes automatically rejected, converting the harmful factor into a demonstration of the differential architecture's noise rejection capability.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Measurement precision

If noise elimination is implemented at the signal conditioning stage, then output noise is reduced, but saturation condition occurs when noise level is sufficiently large

Engineering Contradiction:

Improveoutput signal qualityVSAvoidamplifier saturation

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent applies preliminary noise rejection at the differential amplification stage before subsequent signal conditioning. By rejecting common-mode noise early in the signal chain through differential amplification, the system prevents large noise levels from saturating later stages while maintaining high output signal quality.

Inventive Principle:

Principle #10Preliminary action

4Object-affected harmful factors

If shielded twisted pair cables are used, then common mode noise pickup is reduced, but cable complexity and cost increase

Engineering Contradiction:

Improvecommon mode noise pickupVSAvoidcable structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent converts the potential harm of cable complexity into a benefit by demonstrating that simple twisted pair cables, when used with differential amplification, achieve effective common-mode noise rejection. The twisting provides inherent common-mode rejection without requiring complex shielding structures.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8067947B2Low noise differential charge amplifier for measuring discrete charges in noisy and corrosive environments

Publication Date: 2011.11.29 HONEYWELL INTERNATIONAL INC

AI summary

A low noise differential charge amplifier circuit for measuring discrete (e.g., pico coulomb) charges in noisy, elevated temperature and corrosive environments. An input stage of a differential charge amplifier circuit includes a twisted and or untwisted two pair cable with a grounded shield. One twisted and or untwisted pair can be connected to a sensor and a first charge amplifier and a second twisted and or/untwisted pair can be connected to a sensor electrical equivalent impedance circuit and or kept open and a second charge amplifier. The output from the charge amplifiers can be directed to a differential amplifier in order to provide an amplified sensor signal without external noise signal mainly from power supply mains. The differential amplifier and the charge amplifiers can include an auto offset correction circuit to reduce errors due to offsets.