MEMS Microphone Interface Capacitance for HD2 Linearization
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Solution Overview
Problem
Single-ended MEMS microphones suffer from prominent 2nd order harmonic distortion (HD2) at certain volume levels and frequencies, which affects their performance in consumer applications.
Innovation Solution
An extra non-linear capacitor is added at the interface between the MEMS and ASIC to balance charge transfer, compensating for the intrinsic HD2 by maintaining a constant charge sum, thereby reducing nonlinearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a single-ended MEMS microphone is used, then the device achieves compact form factor and studio-quality audio, but prominent 2nd order harmonic distortion occurs at certain volume levels and frequencies
Solution Approach 1:
A nonlinear capacitance component is introduced as an intermediary element between the MEMS device and the readout circuit. This component has a specific CV profile that compensates for the nonlinearities in the MEMS capacitor, thereby reducing harmonic distortion without requiring changes to the core MEMS structure or signal processing algorithms.
Solution Approach 2:
The invention changes the electrical parameter characteristics by introducing a capacitance component with specific nonlinear CV characteristics. By carefully selecting and tuning the CV profile of the added capacitance, the system optimizes linearity performance across different operating conditions, effectively reducing 2nd order harmonic distortion.
2Measurement precision
If a nonlinear capacitance component is added to compensate for HD2, then system linearity is improved, but device complexity increases
Solution Approach 1:
The nonlinear capacitance component is merged with existing circuit elements at the interface between MEMS and ASIC. By combining the compensation function with the existing readout circuit architecture, the invention achieves linearity improvement without requiring completely separate compensation circuits, thus limiting the increase in device complexity.
3Power
If the MEMS device operates at higher volume levels, then audio output increases, but 2nd order harmonic distortion becomes more prominent
Solution Approach 1:
The nonlinear capacitance component provides preliminary anti-action by pre-compensating for the nonlinearities that will occur during operation. The component is designed with a CV profile that anticipates and counteracts the 2nd order harmonic distortion mechanisms, allowing the system to maintain linearity even at higher operating volumes where distortion would normally become prominent.
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
The harmonic distortion is significantly reduced, improving system linearity and signal quality by up to 20 dB, enhancing performance in consumer devices.
Implementation Method 1
the MEMS device output and the programmable gain amplifier or source follower input comprise a first nonlinear equivalent capacitance having a first capacitance-to-voltage (CV) profile; and a nonlinear capacitance component coupled to the first node, the second node, and at least one reference voltage node, wherein the nonlinear capacitance component comprises a second nonlinear equivalent capacitance having a second CV profile
Data Source
AI summary
A microphone includes a microelectromechanical system (MEMS) device responsive to sound waves or vibrations having an output coupled to a first node; a programmable gain amplifier or source follower having an input coupled to a second node, and an output for generating an analog signal, wherein the MEMS device output and the programmable gain amplifier or source follower input comprise a first nonlinear equivalent capacitance having a first capacitance-to-voltage (CV) profile; and a nonlinear capacitance component coupled to the first node, the second node, and at least one reference voltage node, wherein the nonlinear capacitance component comprises a second nonlinear equivalent capacitance having a second CV profile.