MEMS Microphone Self-Test Using Bias Voltage and Signal Injection
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Solution Overview
Problem
Testing digital microphones is complex and costly due to the need for specialized equipment, and distinguishing between mechanical and analog electronic issues is difficult, leading to increased manufacturing and testing expenses.
Innovation Solution
A digital microphone with built-in self-test capabilities, including a MEMS capacitor, a charge pump for varying bias voltages, a processing chain with a preamplifier, ADC, and sigma delta block, and a multiplexer to compare digitized outputs to expected ranges, allowing for efficient testing of both analog front-end and MEMS capacitor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If specialized acoustic equipment and settings are used for testing digital microphones, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The digital microphone performs self-testing by applying test signals to its own input and analyzing its own output through the processing chain, eliminating the need for external specialized acoustic equipment. The device tests itself using built-in resources including the MEMS capacitor, analog front end, and digital signal processing capabilities.
Solution Approach 2:
The patent replaces complex mechanical acoustic testing equipment with electrical signal processing methods. Instead of using physical acoustic chambers and measurement microphones, the system uses electrical test signals applied to the MEMS capacitor and processed through the analog and digital chains, substituting mechanical measurement systems with electrical equivalents.
2Measurement precision
If specialized acoustic equipment is used for testing, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
By enabling the microphone to test itself without external equipment, the patent eliminates costly specialized acoustic testing chambers and measurement devices from the manufacturing process. The self-test capability uses the microphone's own operational components to perform measurements that would otherwise require expensive external equipment.
Solution Approach 2:
The patent creates a simplified model of the acoustic measurement process using electrical signals. Instead of physically reproducing acoustic conditions with specialized equipment, the system uses electrical test signals that replicate the functional behavior of acoustic inputs, allowing measurement without expensive physical test environments.
3Measurement precision
If it is determined whether mechanical or analog electronic portion does not meet standards, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent divides the microphone into distinct testable segments: the MEMS capacitor (mechanical portion) and the analog front end with digital processing chain. By applying test signals and analyzing responses at different stages, the system can identify which specific segment is malfunctioning without requiring a complex integrated test system.
Solution Approach 2:
The patent uses the signal processing chain as an intermediary to isolate and identify faults. By inserting test signals at different points and analyzing the intermediate outputs, the system can determine whether a fault lies in the mechanical MEMS portion or the analog electronic portion without directly observing the fault source.
4Productivity
If built-in self-test is implemented, then productivity is improved, but device complexity increases
Solution Approach 1:
The patent makes the microphone's processing chain serve multiple functions: normal signal processing and self-testing. The same analog front end, ADC, and digital blocks used for audio processing are also utilized for generating and analyzing test signals, eliminating the need for separate dedicated test hardware and minimizing additional complexity.
Solution Approach 2:
The patent merges the test signal generation and analysis functions with the normal audio processing chain. The MEMS capacitor, preamplifier, ADC, and digital blocks handle both operational audio signals and self-test signals, combining multiple functions into existing components rather than adding separate test systems.
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
Enables cost-effective and efficient testing of digital microphones by applying varying bias voltages and measuring outputs, determining if differences are within acceptable ranges, thereby simplifying the testing process and reducing manufacturing costs.
Implementation Method 1
a MEMS capacitor, the MEMS capacitor serving as a sensor for the digital microphone
Implementation Method 2
electrostatic force is applied in a known varying manner to a MEMS capacitor of a digital microphone
Data Source
AI summary
A digital microphone includes built-in self-test features. The features may include capability to apply different bias voltages to a MEMS capacitor sensor of the digital microphone, simulating application of different sound pressures to the digital microphone. The features may also include a digital oscillator, for applying a test signal to an analog front end of the microphone.