Half-Bridge Circuit for MEMS Sensor Common Mode Compensation
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Solution Overview
Problem
Conventional MEMS sensors face challenges in minimizing chip area due to the need for larger CMOS chips for bonding, which can impact MEMS sensor performance when moving functionality from the MEMS chip to the CMOS chip.
Innovation Solution
Implementing a CMOS half-bridge circuit with compensation capacitors that maintain constant capacitance to counteract common mode injections from MEMS sensors, allowing for efficient transfer of signals and minimizing detectable differences in capacitance changes, thereby optimizing MEMS sensor performance without increasing MEMS chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If functionality is moved from MEMS chip to CMOS chip, then MEMS chip area is reduced, but sensor performance is impacted
Solution Approach 1:
The patent extracts the bridge circuit functionality from the MEMS chip and implements it in the CMOS chip. Specifically, the half-bridge circuit with compensation capacitors is placed in the CMOS chip, allowing the MEMS chip to be smaller while maintaining sensor performance through the extracted compensating functionality.
Solution Approach 2:
The patent introduces compensation capacitors as intermediary elements in the half-bridge circuit. These capacitors act as mediators that compensate for common mode injections and parasitic effects, enabling the transfer of functionality to the CMOS chip while preserving sensor accuracy and performance.
2Measurement precision
If full capacitive bridge is used, then sensor accuracy is maintained, but chip area increases
Solution Approach 1:
The patent segments the full capacitive bridge into a half-bridge configuration. By using only one arm of the bridge (the other arm being implemented as compensation capacitors in CMOS), the chip area is reduced while maintaining sensor accuracy through the segmented approach that preserves differential signaling capability.
Solution Approach 2:
The patent changes the configuration parameter of the bridge circuit from a full bridge to a half-bridge topology. This parameter change allows the system to maintain measurement precision by using compensation capacitors with specific capacitance values that counteract common mode injections, while reducing the physical area required on the MEMS chip.
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 solution enables effective compensation for common mode injections, maintaining sensor accuracy and reducing the need for larger CMOS chips, thus preserving MEMS sensor performance while minimizing chip area.
Implementation Method 1
a first capacitor and a second capacitor of the half-bridge circuit are configured to maintain constant capacitance to compensate for common mode injections from the MEMS sensor
Data Source
AI summary
A circuit includes a sensor and a half-bridge circuit. The sensor includes a first sensor capacitor and a second sensor capacitor, where capacitances of the first sensor capacitor and the second sensor capacitor change in opposing directions responsive to receiving a physical signal. The sensor generates a plurality of sensor signals according to the physical signal, the plurality of signals including a common mode injection and a plurality of differential signals. The half-bridge circuit includes a first half-bridge capacitor and a second half-bridge capacitor, where capacitances of the first half-bridge capacitor and the second half-bridge capacitor compensate for the common mode injection of the plurality of sensor signals. The sensor and the half-bridge circuit are coupled to a plurality of sense nodes configured to output the plurality of differential signals.