Differential MEMS Sensor Amplifier Layout for Low Distortion
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Solution Overview
Problem
Conventional MEMS microphone amplifier circuits face challenges with high power consumption, total harmonic distortion, and reduced common-mode rejection due to single-ended layouts and conflicting design requirements.
Innovation Solution
A fully differential circuit layout with a feedback network using resistors and an additional amplifier stage to manage common-mode signals, coupled with capacitive feedback and diodes, is introduced to improve signal processing and reduce distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-ended layout is used in the amplifier circuit, then the device complexity is reduced, but the common-mode rejection is degraded and total harmonic distortion increases
Solution Approach 1:
The amplifier circuit is divided into two symmetrical amplifier stages (first and second stages) that process differential signals separately. Each stage handles one side of the differential pair, allowing independent optimization of each path while maintaining overall circuit performance and common-mode rejection.
Solution Approach 2:
The patent introduces an asymmetrical feedback network with resistors of different values (first and second resistors with different resistance values) connected to the differential outputs. This asymmetrical configuration is specifically designed to cancel common-mode signals while preserving differential signal integrity, thereby improving common-mode rejection without requiring a fully symmetrical differential layout.
2Device complexity
If a single-ended layout is used in the amplifier circuit, then the device complexity is reduced, but the total harmonic distortion increases
Solution Approach 1:
The amplifier circuit is divided into two symmetrical amplifier stages (first and second stages) that process differential signals separately. Each stage handles one side of the differential pair, allowing independent optimization of each path while maintaining overall circuit performance and common-mode rejection.
Solution Approach 2:
The patent introduces an asymmetrical feedback network with resistors of different values (first and second resistors with different resistance values) connected to the differential outputs. This asymmetrical configuration is specifically designed to cancel common-mode signals while preserving differential signal integrity, thereby improving common-mode rejection without requiring a fully symmetrical differential layout.
3Power
If high power consumption is used in the amplifier circuit, then the output signal amplitude is increased, but the energy efficiency is reduced
Solution Approach 1:
The patent implements a feedback network connecting the differential outputs back to the inputs of the amplifier stages through resistors. This feedback mechanism stabilizes the gain, extends the bandwidth, and improves the linearity of the amplifier, allowing it to achieve the required output signal amplitude with optimized power consumption rather than relying solely on high power input.
Data Source
AI summary
A circuit for amplifying signals from a Micro Electro-Mechanical System (MEMS) capacitive sensor is provided. First and second input nodes receive a sensing signal applied differentially between the input nodes. A first amplifier stage and a second amplifier stage, respectively, produce a differential output signal between first and second output nodes. A common mode signal is detected at the output nodes. A voltage divider having an intermediate tap node is coupled between the first output node and the second output node. A feedback stage is coupled between the tap node of the voltage divider and the inputs of the first amplifier stage and the second amplifier stage, where the feedback line is sensitive to the common mode signal at the output nodes.