Capacitive Sensor Trace Balancing for RF Interference Rejection
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Solution Overview
Problem
Capacitive sensing devices are prone to signal distortion due to electrical interference from sources like LCDs and RF transmitters, which corrupt the signals produced by these devices.
Innovation Solution
The solution involves forming routing traces with varying resistivity materials to create an impedance mismatch, allowing them to act as RF reflectors and reduce interference, while ensuring balanced RC time constants across traces to handle common mode interference effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If routing traces of different lengths are used to connect sensor electrodes, then the sensing coverage and area are improved, but electrical interference and signal distortion increase due to varying RC time constants
Solution Approach 1:
The patent applies local quality by adding different resistance values to different routing traces based on their individual characteristics. Each routing trace is assigned a specific resistance value that compensates for its length and capacitance, creating localized impedance matching that equalizes RC time constants across all traces regardless of their varying lengths.
Solution Approach 2:
The patent changes the electrical parameters (resistance values) of the routing traces to achieve equal RC time constants. By adjusting the resistance parameter of each trace according to its capacitance and length, the system transforms traces with different physical dimensions into electrically equivalent pathways, eliminating the harmful effect of varying RC time constants on sensing accuracy.
2Adaptability or versatility
If routing traces are made longer to expand sensing coverage, then the sensing capability is improved, but the traces act as antennas that pick up RF interference
Solution Approach 1:
The patent converts the harmful effect of long routing traces acting as RF antennas into a benefit by adding resistance to create impedance mismatches. This impedance mismatch prevents RF signals from coupling efficiently onto the traces, effectively suppressing antenna effects while preserving the extended sensing coverage provided by the longer traces.
Solution Approach 2:
The patent changes the electrical parameters of the routing traces by introducing resistance elements, which modifies the impedance characteristics. This parameter change disrupts the resonant conditions that would allow RF interference to couple onto the traces, thereby reducing antenna effects while maintaining the extended sensing capability.
3Ease of manufacture
If uniform routing traces are used across all sensor electrodes, then the manufacturing process is simplified, but traces of different lengths have different RC time constants causing signal distortion
Solution Approach 1:
The patent applies local quality by introducing non-uniform resistance values at specific locations along the routing traces. Instead of making all traces identical, it locally adjusts the resistance of each trace according to its specific length and capacitance, creating customized electrical characteristics that equalize RC time constants while maintaining manufacturing feasibility through systematic resistance addition.
Solution Approach 2:
The patent changes the electrical parameters of the routing traces by adding resistance elements with specific values tailored to each trace's characteristics. This parameter adjustment transforms traces with inherently different RC time constants into electrically equivalent pathways, improving signal accuracy without requiring complete redesign of the manufacturing process.
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 significantly reduces electrical interference, enabling better recognition and removal of common mode RF noise, allowing for variable sensing frequencies and reduced clock modulation jitter without significant programming overhead.
Implementation Method 1
The solution involves forming routing traces with varying resistivity materials to create an impedance mismatch, allowing them to act as RF reflectors and reduce interference
Implementation Method 2
The solution involves forming routing traces with varying resistivity materials to create an impedance mismatch, allowing them to act as RF reflectors and reduce interference
Implementation Method 3
To attenuate electrical interference, the second routing trace is formed having an approximately equal RC time constant characteristic as the first routing trace
Implementation Method 4
The solution involves forming routing traces with varying resistivity materials to create an impedance mismatch, allowing them to act as RF reflectors and reduce interference, while ensuring balanced RC time constants across traces to handle common mode interference effectively
Data Source
AI summary
Embodiments for a capacitive sensing apparatus with attenuated electrical interference across a plurality of routing traces are provided. One embodiment forms a first sensor electrode on a substrate. In addition, a first routing trace is formed on the substrate, the first routing trace coupled with the first sensor electrode. One embodiment additionally forms a second sensor electrode on the substrate. A second routing trace differing in length from the first routing trace is also formed on the substrate, the second routing trace coupled with the second sensor electrode. To attenuate electrical interference, the second routing trace is formed having an approximately equal RC time constant characteristic as the first routing trace.