Nonlinear capacitance and distortion reduction in dual backplate condenser microphones.

Area of Science:

• Acoustics
• Microphone technology
• MEMS devices

Background:

• Dual backplate microphones offer improved sensitivity, dynamic range, and reduced even-order harmonic distortion over single backplate designs.
• Nonlinear behavior in microphones, particularly capacitance changes, is a key factor affecting distortion.

Purpose of the Study:

• To investigate the nonlinear behavior and distortion mechanisms in dual backplate microphones.
• To develop and validate a theoretical model for harmonic distortion in these devices.
• To explore methods for further reducing distortion in dual backplate microphone designs.

Main Methods:

• Development of a theoretical model analyzing nonlinear capacitance changes due to air gap and parasitic capacity asymmetries.
• Validation of the theoretical model through acoustic measurements on a dual backplate micro-electro-mechanical systems (MEMS) microphone.
• Adaptation and application of a signal-domain correction algorithm for distortion reduction.

Main Results:

• The theoretical model confirmed that symmetrical air gaps and parasitic capacities significantly decrease second-harmonic distortion.
• The dual backplate structure effectively cancels even-order harmonics.
• The adapted signal-domain correction algorithm further reduced distortion in dual backplate microphones.

Conclusions:

• Asymmetries in air gaps and parasitic capacities are primary contributors to harmonic distortion in dual backplate microphones.
• Dual backplate microphone design inherently suppresses even-order harmonics.
• The study provides a validated model and practical algorithms for enhancing the performance of dual backplate microphones in demanding acoustic applications.