Resistive Force Sensor Common Mode Offset Control
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Solution Overview
Problem
Resistive force sensors in electronic devices face challenges due to resistance variations caused by fabrication process inconsistencies, leading to common mode offset issues, which limit their ability to accurately measure force across a continuum of values.
Innovation Solution
The implementation of individual strain sensitive structures on substrates with external resistors and signal generators to adjust and balance resistances, reducing common mode offset through differential amplifiers and digitally controlled signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain sensitive structures are used to detect force, then force measurement capability is provided, but resistance variations cause common mode offset that reduces measurement accuracy
Solution Approach 1:
The patent applies parameter changes by using digitally controlled resistors to dynamically adjust and balance the resistance values of strain sensitive structures. The system modifies the electrical parameters (resistance) to compensate for fabrication variations, thereby reducing common mode offset and improving measurement accuracy and reliability
Solution Approach 2:
The patent implements feedback mechanisms through differential amplifiers that continuously monitor the output signals from strain sensitive structures. The system uses the detected common mode offset as feedback to adjust the digitally controlled resistors, creating a closed-loop control system that maintains measurement accuracy despite resistance variations
2Reliability
If external resistors are added to balance strain sensitive structures, then common mode offset is reduced, but device complexity increases
Solution Approach 1:
The patent uses digitally controlled resistors that can be programmed to specific resistance values, allowing precise balancing of strain sensitive structures. This digital control approach provides reliable common mode rejection while maintaining a compact and programmable circuit design
Solution Approach 2:
The patent introduces digitally controlled resistors as intermediary elements between the strain sensitive structures and the differential amplifiers. These resistors act as mediators that balance the resistance values without requiring complex circuit modifications, thus improving reliability with minimal increase in overall device complexity
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 approach effectively reduces common mode offset, enabling accurate measurement of force applied to electronic devices by minimizing resistance differences between strain sensitive structures.
Implementation Method 1
force is determined by detecting changes in resistance between multiple strain sensing elements
Implementation Method 2
The external resistor(s) effectively increases the resistances of the first and/or second strain sensitive structure to reduce the common mode offset
Data Source
AI summary
Several techniques for driving a force sensor to reduce common mode offset are disclosed. The force sensor can include at least one set of individual strain sensitive structures formed on or in a surface of a substrate. Each set of individual strain sensitive structures can include one or more strain sensitive structures. At least one external resistor is operably connected in series between a first output of one or more transmitter channels and at least one set of strain sensitive structures. The external resistor(s) effectively increases the resistances of the strain sensitive structures to reduce the common mode offset. Additionally or alternatively, one or more signal generators may be connected to one or more transmitter channels. Each signal generator is configured to produce one or more signals that is/are designed to reduce common mode offset.