Comparator-Based Common Mode Control for Capacitive Sensor Amplifiers

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Solution Overview

Problem

Capacitive inertial sensor circuits face performance degradation due to high system noise and reduced operation speed caused by large feedback capacitance in switch-capacitor common mode voltage control circuits, which are unable to quickly and precisely recover desired common mode voltage.

Innovation Solution

A full voltage swing common mode voltage comparator circuit is configured in parallel to the common mode feedback control circuit to rapidly and efficiently compensate for input common mode signal variations, minimizing overall amplifier input capacitance and optimizing system performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If switch-capacitor common mode voltage control circuits are used, then common mode voltage control is achieved, but system noise increases and operation speed decreases due to large feedback capacitance

Engineering Contradiction:

Improvecommon mode voltage controlVSAvoidsystem noise

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the traditional switch-capacitor common mode voltage control circuit with a dedicated comparator circuit. This substitution eliminates the need for large feedback capacitance, thereby reducing system noise while maintaining common mode voltage control functionality. The comparator circuit provides a more efficient control mechanism that does not rely on capacitive feedback.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control mechanism from analog switch-capacitor based control to a comparator-based control with defined threshold voltages (VCMH and VCMC). This parameter change allows for precise control of common mode voltage within a specific range without requiring large feedback capacitance, thus reducing noise while maintaining control reliability.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If switch-capacitor common mode voltage control circuits are used, then common mode voltage control is achieved, but operation speed is reduced due to inability to quickly recover desired common mode voltage

Engineering Contradiction:

Improvecommon mode voltage controlVSAvoidoperation speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces the slow switch-capacitor control mechanism with a dedicated comparator circuit that can rapidly detect common mode voltage deviations and generate corrective signals. This substitution enables quick recovery of the desired common mode voltage, significantly improving operation speed while maintaining control reliability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent implements a feedback mechanism using the dedicated comparator that continuously monitors the common mode voltage and compares it against reference thresholds. When deviations are detected, the comparator generates feedback signals to adjust the control voltage, enabling rapid recovery and maintaining high operation speed.

Inventive Principle:

Principle #23Feedback

3Stability of the object's composition

If large feedback capacitance is used in common mode control circuits, then common mode voltage control stability is improved, but amplifier noise performance deteriorates

Engineering Contradiction:

Improvecommon mode voltage control stabilityVSAvoidamplifier noise

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent substitutes the large feedback capacitance-based control with a dedicated comparator circuit that achieves stability through voltage threshold comparison rather than capacitive feedback. This elimination of large capacitance directly reduces amplifier noise while maintaining control stability through the comparator's threshold-based control mechanism.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the stability mechanism from capacitive feedback to voltage threshold comparison. By defining specific threshold voltages (VCMH and VCMC) and using the comparator to enforce these thresholds, the system achieves stable common mode voltage control without requiring large feedback capacitance, thereby reducing amplifier noise.

Inventive Principle:

Principle #35Parameter changes

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 reduces system noise and increases operation speed by allowing for more precise control of common mode voltage, enhancing the noise performance and efficiency of capacitive sensor front end electronics.

Implementation Method 1

a first input of the comparator is coupled to receive an input common mode voltage; a second input of the comparator is coupled to receive a first common mode reference voltage

Methodology Applied

Scientific EffectVoltage comparison:

Data Source

PatentUS8884699B2Input common mode control using a dedicated comparator for sensor interfaces

Publication Date: 2014.11.11 MAXIM INTEGRATED PROD INC

AI summary

Various embodiments of the invention allow for low-noise, high performance input common mode voltage control in capacitive sensor front end amplifiers. In certain embodiments overcome the shortcomings of the prior art by implementing a full voltage swing common mode voltage comparator in a parallel feed-forward path to compensate large common mode input signal variations.