MEMS Speaker Drive Circuit With Positive Offset Voltage Floor

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Solution Overview

Problem

Piezoelectric elements in MEMS speakers deteriorate due to depolarization caused by negative voltages, especially when noise is introduced into the drive signal, leading to harmonic distortion and degraded sound quality.

Innovation Solution

A drive circuit with an amplifier and offset generators are used to ensure the minimum absolute value of the drive signal voltage is greater than a positive predetermined voltage, suppressing negative voltages and maintaining polarization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a positive drive signal is supplied to the piezoelectric element to suppress depolarization, then the piezoelectric characteristics are maintained, but noise or other signals may introduce negative voltages that cause deterioration

Engineering Contradiction:

Improvepiezoelectric characteristics maintenanceVSAvoidnegative voltage damage

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The offset generator pre-adds a positive offset voltage to the drive signal before it reaches the piezoelectric element. This preliminary action ensures that even when noise or other negative voltage components are present in the signal, the total voltage applied to the piezoelectric element remains positive, thereby preventing depolarization and maintaining reliable piezoelectric characteristics throughout operation.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If noise is added to the drive signal, then signal fidelity may be improved through dynamic range, but negative voltage components cause depolarization and deterioration

Engineering Contradiction:

Improvesignal dynamic rangeVSAvoidpiezoelectric element durability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention converts the potentially harmful offset voltage into a beneficial protective element. By deliberately adding a positive offset voltage through the offset generator, the system creates a voltage floor that transforms the drive signal into a form that can tolerate noise and dynamic variations without risking negative voltage application. This offset acts as a protective buffer that maintains signal dynamic range while ensuring piezoelectric element durability.

Inventive Principle:

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

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 prevents depolarization and harmonic distortion, enhancing sound quality by ensuring the drive signal maintains a positive minimum voltage, thus preserving the piezoelectric characteristics of the MEMS speaker.

Implementation Method 1

A piezoelectric body of a piezoelectric element is polarized by applying a DC voltage to the piezoelectric body. The piezoelectric body maintains a polarized state even after the DC voltage applied to the piezoelectric body is removed.

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

an amplifier configured to amplify an input signal, and supply the amplified input signal as a drive signal to a piezoelectric element

Methodology Applied

Scientific EffectElectrical amplification:

Implementation Method 3

an offset generator configured to generate an offset such that a minimum absolute value of a voltage of the drive signal is greater than or equal to a positive predetermined voltage

Methodology Applied

Scientific EffectVoltage offset generation:

Data Source

PatentUS20250310687A1Drive circuit and electro-acoustic conversion system

Publication Date: 2025.10.02 MITSUMI ELECTRIC CO LTD

AI summary

A drive circuit includes an amplifier configured to amplify an input signal, and supply the amplified input signal as a drive signal to a piezoelectric element of a MEMS (Miro-Electro-Mechanical Systems) speaker driven by a piezoelectric element; and an offset generator configured to generate an offset such that a minimum absolute value of a voltage of the drive signal is greater than or equal to a positive predetermined voltage.