Dual-Backplate MEMS Microphone Amplifier With Distortion Feedback
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Solution Overview
Problem
MEMS microphones experience signal distortion due to asymmetric current drive capability of source followers when processing large signal amplitudes, particularly when loaded with a capacitive load, leading to increased noise levels.
Innovation Solution
The amplifier incorporates a second source follower connected to the second backplate of the dual backplate MEMS microphone and includes a distortion detection circuit that measures output signal distortion, connected to a correctional circuit to adjust the bias current source for the first source follower, ensuring appropriate current levels are maintained to prevent distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If damping is applied to reduce peak response at resonance frequency, then microphone sensitivity is improved, but noise levels increase
Solution Approach 1:
The patent converts the harmful effect of resonance peak into a benefit by using feedback to cancel it out. The feedback network detects the resonance peak and applies a compensating signal to flatten the frequency response, thereby improving sensitivity across the audible range without introducing additional noise.
Solution Approach 2:
The patent employs feedback mechanisms where the output signal is fed back to the input through a feedback network. This feedback is used to detect and cancel resonance peaks, adjust bias currents, and maintain optimal operating conditions, thereby improving sensitivity while controlling noise levels.
2Object-generated harmful factors
If a relatively large capacitor is used in the low-pass filter, then noise is kept low, but the filter size and power consumption increase
Solution Approach 1:
The patent dynamically changes operating parameters, specifically bias currents, based on signal conditions. By adjusting bias currents in response to signal amplitude and distortion levels, the system maintains low noise performance while optimizing power consumption according to actual operating needs rather than using fixed high values.
Solution Approach 2:
The patent introduces dynamic adjustment mechanisms that adapt the amplifier's operating characteristics in real-time. The bias current adjustment circuit and distortion detection circuit work together to dynamically optimize performance, allowing the system to maintain low noise when needed while reducing power consumption during normal operation.
3Manufacturing precision
If the source follower provides high current to handle large signal amplitudes, then signal distortion is reduced, but power consumption increases
Solution Approach 1:
The patent makes the bias current dynamic rather than fixed. The bias current adjustment circuit responds to signal conditions and distortion levels, increasing current only when necessary to handle large signals or correct distortion, and reducing current during normal operation to minimize power consumption.
Solution Approach 2:
The distortion detection circuit provides feedback about signal quality to the bias current adjustment circuit. This feedback loop enables the system to automatically increase bias current when distortion is detected (indicating high signal amplitudes) and reduce current when distortion is minimal, thereby optimizing the trade-off between distortion and power consumption.
Data Source
AI summary
An amplifier for a dual backplate MEMS microphone comprising at least a first source follower which has a gate for connection to a first backplate of the dual backplate MEMS microphone, and a load circuit connected to a source of the first source follower which provides an output signal of the filter, which filter comprises a second source follower connected to a second backplate of the dual backplate MEMS microphone, and a distortion detection circuit which is connected to the source of the first source follower and to the source of the second source follower for measuring distortion of the output signal at the source of the first source follower, wherein said distortion detection circuit is connected to a correctional circuit that drives at least a first bias current source for the first source follower.