Source Follower Feedback Circuit for MEMS Microphone Sensitivity
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Solution Overview
Problem
As MEMS sensors, such as those in microphone systems, shrink to reduce package size, their sensitivity decreases, necessitating a solution to enhance signal amplification while maintaining or improving sensitivity.
Innovation Solution
A circuit and method utilizing a differential amplifier with capacitive feedback, including a programmable capacitor and AC coupling capacitors, to provide configurable gain or attenuation, allowing for adjustable sensitivity in MEMS microphone systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If MEMS sensors are shrunk to reduce package size, then device size is reduced, but sensitivity decreases
Solution Approach 1:
The patent implements a feedback mechanism where the output of the source follower is fed back to its input through a feedback network. This feedback loop compensates for the reduced sensitivity by amplifying the weak signals from shrunk MEMS sensors, effectively resolving the contradiction between smaller package size and maintained sensitivity
Solution Approach 2:
The patent changes the electrical parameters of the source follower circuit, specifically adjusting the feedback factor and gain parameters to compensate for the reduced sensor sensitivity. By modifying these circuit parameters, the system maintains measurement precision despite the physical shrinkage of the MEMS sensor
2Measurement precision
If signal amplification is increased to compensate for reduced sensitivity, then sensitivity is improved, but noise increases
Solution Approach 1:
The negative feedback mechanism in the source follower circuit amplifies only the differential signal while suppressing common-mode noise. The feedback network is designed to reject noise components that are present at both inputs, thereby improving sensitivity without proportionally increasing noise
Solution Approach 2:
The source follower circuit maintains equipotential conditions at the input nodes, which helps in rejecting common-mode noise. By keeping the input nodes at the same potential level for common-mode signals, the circuit differentiates between desired differential signals and unwanted noise
3Measurement precision
If signal amplification is increased to compensate for reduced sensitivity, then sensitivity is improved, but power consumption increases
Solution Approach 1:
The source follower circuit dynamically adjusts its operating point and gain based on the input signal level. This dynamic operation allows the circuit to provide high amplification only when needed for weak signals, reducing average power consumption while maintaining sensitivity for low-level signals
Solution Approach 2:
The source follower circuit self-regulates its power consumption by automatically adjusting its operating parameters based on the signal conditions. The feedback mechanism ensures that the circuit consumes minimal power while providing sufficient amplification for the reduced-sensitivity MEMS sensors
Data Source
AI summary
In accordance with an embodiment, a circuit includes an amplifier and a programmable capacitor coupled between an output of the first non-inverting and the input of the first amplifier.