Charge Amplifier Multi-Phase Reset for Offset Voltage Cancellation

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Solution Overview

Problem

Existing charge amplifier circuits suffer from offset errors that deteriorate accuracy and are exacerbated by changes in capacitance and gain, leading to inefficiencies in signal processing.

Innovation Solution

A multi-phase reset process involving specific switch configurations and capacitor connections within the charge amplification circuit to effectively cancel offset voltages, ensuring complete offset voltage cancellation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a charge amplifier circuit is used to convert charge variation into voltage signal, then signal processing capability is improved, but offset voltage error deteriorates measurement accuracy

Engineering Contradiction:

ImproveaccuracyVSAvoidoffset voltage error

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by performing offset voltage cancellation before the main measurement operation. The circuit executes a reset phase that precedes the measurement phase, during which offset voltages are detected and cancelled in advance, ensuring accurate measurements during subsequent operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the harmful offset voltage into a beneficial signal by using it to generate a cancellation signal. The offset voltage that would normally degrade accuracy is instead captured during the reset phase and used to create an equal and opposite cancellation signal that eliminates the offset error.

Inventive Principle:

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

2Speed

If capacitance in the feedback branch is reduced to improve response speed, then bandwidth is increased, but offset voltage error grows

Engineering Contradiction:

Improveresponse speedVSAvoidoffset voltage error

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful effect of reduced capacitance (amplified offset error) into a benefit by using the same reset mechanism to cancel the offset. The low-capacitance design for high bandwidth is maintained, while the reset phase captures and cancels the resulting offset errors.

Inventive Principle:

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

Solution Approach 2:

The patent implements feedback by using the offset voltage detected during the reset phase to generate a cancellation signal that is fed back to eliminate the offset error. This feedback mechanism ensures that offset errors are continuously corrected without requiring high feedback capacitance.

Inventive Principle:

Principle #23Feedback

3Power

If gain from the offset source is increased to amplify signal, then signal amplification is improved, but offset voltage error grows

Engineering Contradiction:

Improvesignal amplificationVSAvoidoffset voltage error

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent converts the harmful amplified offset error into a benefit by using the same high-gain mechanism to amplify both the signal and the offset, then using the amplified offset to generate an equal and opposite cancellation signal that eliminates the error while preserving the signal.

Inventive Principle:

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

4Measurement precision

If multi-phase reset process is implemented to cancel offset voltage, then offset cancellation accuracy is improved, but circuit operation complexity increases

Engineering Contradiction:

Improveoffset cancellation accuracyVSAvoidcircuit operation complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges the offset cancellation function with the existing reset operation of the charge amplifier. By combining these functions, the circuit achieves accurate offset cancellation without requiring separate dedicated cancellation circuitry, thus reducing overall complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent makes the reset phase multi-functional by having it serve both the traditional reset function and the offset cancellation function. This universal approach allows a single phase to accomplish multiple objectives without requiring additional dedicated phases or circuitry.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12549145B2Offset voltage cancelation for a charge amplification circuit

Publication Date: 2026.02.10 STMICROELECTRONICS INT NV

AI summary

A circuit includes an amplifier, a bias voltage node, and a first set of switches configured, based on a first reset signal being asserted, to couple amplifier input nodes to the bias voltage node and to short-circuit amplifier output nodes. First and second feedback branches each include a respective circuit network including parallel capacitors, with first ones of the capacitors directly connected to the amplifier input nodes. The first and second feedback branches further include a second set of switches intermediate the amplifier input nodes and second ones of the capacitors, and a third set of switches intermediate amplifier output nodes and the capacitors. These switches selectively couple the capacitors to the amplifier input and output nodes, based on a second reset signal being asserted. The second reset signal is asserted for a time interval exceeding a time interval in which the first reset signal is asserted.