Capacitive Transducer Noise Cancellation via Nested Dual Capacitors
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Solution Overview
Problem
Capacitive transducers face challenges in improving signal-to-noise ratio (SNR) due to noise generated within the microphone, which is difficult to cancel using existing techniques, especially when noise sources are internal and affect both microphones independently.
Innovation Solution
The solution involves configuring two capacitors with a common vibration electrode, where signals from the first and second capacitors are added to cancel noise, with adjusted electrode areas, positions, inter-electrode gaps, and voltages to ensure equivalent noise levels, allowing for effective noise cancellation and improved SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If two separate microphones are used for noise cancellation, then noise from external sources can be canceled, but the device complexity increases and internal noise cannot be effectively canceled
Solution Approach 1:
The single microphone is segmented into two independent capacitive transducers (first and second capacitors) that share a common vibration electrode film. Each capacitor independently detects acoustic signals and generates noise, allowing separate signal processing while maintaining a compact single-microphone structure. This segmentation enables noise cancellation functionality without requiring two separate microphone devices.
Solution Approach 2:
The vibration electrode film is merged to serve as a common moving electrode for both the first and second capacitors. This shared component generates correlated noise signals in both capacitors, enabling effective noise cancellation through signal subtraction while reducing overall device complexity compared to using two completely independent microphones.
2Measurement precision
If multiple vibration electrode plates are disposed in parallel on one semiconductor substrate, then SN ratio can be improved, but the size becomes large
Solution Approach 1:
The first and second capacitors are nested in series along the acoustic signal path, with the vibration electrode film positioned between the back plate (first fixed electrode) and the semiconductor substrate (second fixed electrode). This nested configuration allows both capacitors to share the same physical space and acoustic pathway, improving SN ratio through correlated noise cancellation without increasing the lateral footprint of the device.
3Object-affected harmful factors
If noise levels of the two capacitors are made equivalent through parameter adjustment, then effective noise cancellation is achieved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent adjusts parameters such as electrode areas, inter-electrode gaps, and operating voltages of the first and second capacitors to equate their noise levels. By modifying these physical and electrical parameters, the invention achieves balanced noise characteristics that enable effective noise cancellation, while the parameter adjustments are designed to be compatible with existing manufacturing tolerances.
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 configuration reliably improves the SNR of the capacitive transducer system by canceling noise while maintaining signal integrity, reducing the burden on the controller, and allowing for more flexible noise cancellation in the capacitive transducer system.
Implementation Method 1
a first capacitor is made up of a first fixed electrode provided in the back plate and the vibration electrode film, and displacement of the vibration electrode film is converted into a change in capacitance of the first capacitor
Implementation Method 2
a noise based on Brownian motion of air accumulated between the semiconductor substrate and the vibration electrode film
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
Provided is a technique capable of improving an SN ratio of a capacitive transducer system, with a more reliable or simpler configuration. A capacitive transducer system is provided with: an acoustic sensor, which includes two fixed electrodes being a fixed electrode film and a substrate, and a vibration electrode film disposed between the fixed electrode film and the substrate so as to face both the fixed electrode film and the substrate through gaps, and in which a first capacitor is made up of the fixed electrode film and the vibration electrode film, and a second capacitor is made up of the substrate and the vibration electrode film, the acoustic sensor being configured to convert transformation of the vibration electrode film into changes in capacitance in the first capacitor and the second capacitor; and an ASIC configured to process voltages supplied to the first capacitor and the second capacitor and/or signals respectively from the first capacitor and the second capacitor. The signals from the first capacitor and the second capacitor are added or subtracted so as to cancel each other.