Capacitive Touch Sensor Shielding During NFC Transmission
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Solution Overview
Problem
Near field communication antennas in close proximity to touch sensors cause electromagnetic interference when transmitting, disrupting the operation of capacitance-sensitive touch sensors like the CIRQUE Corporation touchpad.
Innovation Solution
The touch sensor dynamically shields itself by grounding specific perimeter electrodes when the near field communication antenna is transmitting, preventing electromagnetic interference from reaching the interior electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a near field communication antenna is placed in close proximity to a touch sensor, then the device can provide near field communication functionality, but electromagnetic interference occurs when the antenna transmits, disrupting touch sensor operation
Solution Approach 1:
The touch sensor electrodes are divided into two functional groups: perimeter electrodes that serve as shield electrodes for electromagnetic shielding, and interior electrodes that perform touch sensing functions. This segmentation allows the same electrode structure to provide both shielding and sensing capabilities simultaneously.
Solution Approach 2:
The perimeter electrodes of the touch sensor serve dual functions: they act as shield electrodes to block electromagnetic interference from the near field communication antenna, and they also function as touch sensing electrodes to detect touches at the edges of the touch surface. This multi-functionality eliminates the need for separate shielding structures.
2Object-affected harmful factors
If shielding structures are added to protect the touch sensor from electromagnetic interference, then interference resistance improves, but device complexity increases
Solution Approach 1:
The perimeter electrodes perform dual functions as both shield electrodes for electromagnetic shielding and as touch sensing electrodes for detecting touches. This eliminates the need for separate shielding structures, maintaining device simplicity while providing effective interference protection.
Solution Approach 2:
The touch sensor's own perimeter electrodes are repurposed to provide shielding functionality, eliminating the need for external or additional shielding components. The system uses its existing structure to protect itself from electromagnetic interference.
3Object-affected harmful factors
If perimeter electrodes are used as shield electrodes, then electromagnetic interference is reduced, but touch sensing capability at the edges may be affected
Solution Approach 1:
The controller alternates between different operational modes: during near field communication transmission, perimeter electrodes function as shield electrodes; during touch sensing phases, they function as sensing electrodes. This periodic switching allows both shielding and edge touch detection to work effectively without permanent compromise.
Solution Approach 2:
The functional role of the perimeter electrodes is dynamically switched between shielding and sensing modes based on operational requirements. The controller can adaptively change the electrode configuration to optimize for either interference protection or touch detection depending on the current operational state.
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 allows the touch sensor to continue operating effectively even when the near field communication antenna is active, ensuring reliable touch signal detection and tracking without significant operational impact.
Implementation Method 1
the perimeter electrodes of the touch sensor may be controlled by being individually addressed, a specific signal or action may be performed on each perimeter electrode... The perimeter electrodes 38 may be repurposed. Instead of functioning as a touch sensor electrode that receives touch data, the perimeter electrodes are repurposed by being grounded to provide dynamic shielding of the remaining interior electrodes
Implementation Method 2
When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area 18 of the touchpad 10), a change in capacitance occurs on the electrodes 12, 14
Data Source
AI summary
A system and method for reducing interference caused by a near field communication antenna that is in close proximity of a touch sensor that the near field communication antenna will cause electromagnetic interference with operation of the touch sensor when the near field communication antenna is transmitting, wherein specific electrodes of the touch sensor are grounded when the near field communication antenna is actively transmitting a signal, thereby enabling the touch sensor to continue operating at the same time as the near field communication antenna.