Stylus Signal Rejection in Capacitive Touch Sensors
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Solution Overview
Problem
Capacitive touch sensors face challenges in distinguishing between intentional inputs from a stylus and spurious contacts from a user's hand, particularly when the user holds a stylus and intends to make inputs with their hand simultaneously.
Innovation Solution
A system comprising a capacitive touch sensor and a stylus configured to transmit a first electrical signal through its exterior surface, which is sensed by the touch sensor. The system uses processors to determine if the changes in electrical charge include the signal and to identify contacts as spurious based on the stylus's orientation and the presence of the signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the capacitive touch sensor registers all contacts on the input surface, then it can detect both stylus inputs and hand contacts, but it cannot distinguish between intentional stylus inputs and spurious hand contacts
Solution Approach 1:
The patent introduces an intermediary electrical signal transmitted through the stylus body that acts as a mediator between the stylus and the capacitive touch sensor. This signal serves as a unique identifier that allows the system to distinguish stylus contacts from hand contacts without requiring changes to the fundamental capacitive sensing mechanism. The intermediary signal resolves the contradiction by enabling accurate differentiation while maintaining reliable input registration.
Solution Approach 2:
The patent changes the electrical parameters of the contact by introducing a transmitted electrical signal through the stylus body. This parameter change creates a distinguishable characteristic in the capacitive sensor readings, allowing the system to differentiate between stylus and hand contacts based on the presence and characteristics of the transmitted signal, thereby improving both measurement precision and reliability.
2Measurement precision
If the system rejects contacts identified as spurious, then it improves accuracy for stylus use, but it may incorrectly reject valid hand inputs when the user holds the stylus in their hand
Solution Approach 1:
The patent applies local quality by transmitting the electrical signal selectively through specific portions of the stylus body that come into contact with the user's hand. This localized signal transmission ensures that only contacts where the stylus body touches the hand generate the spurious signal, while valid hand inputs made without stylus body contact remain unaffected. This resolves the contradiction by enabling accurate differentiation without compromising hand input usability.
Solution Approach 2:
Instead of trying to identify valid inputs by absence of spurious signals, the patent inverts the approach by using the presence of the transmitted electrical signal as the definitive marker for stylus-related contacts. This inversion allows the system to confidently reject only those contacts that exhibit both the spurious signal characteristic and occur in contexts consistent with hand resting, while preserving all legitimate hand inputs that lack this signature.
3Reliability
If the stylus transmits an electrical signal through its body, then it enables spurious contact identification, but it increases device complexity
Solution Approach 1:
The patent achieves multi-functionality by designing the stylus body to serve dual purposes: as the structural component the user holds and as a signal transmission medium. The same physical structure that provides ergonomic handling also functions as the conduit for the electrical signal, eliminating the need for separate signaling components and reducing overall device complexity while maintaining reliable contact identification.
Solution Approach 2:
The stylus body serves itself by using its own physical structure as the signal transmission path. The electrical signal travels through the existing material of the stylus body without requiring additional wires, conductors, or complex internal circuitry. This self-service approach enables reliable contact identification while minimizing the increase in 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
Effectively differentiates between intentional stylus inputs and spurious hand contacts, enhancing the accuracy and reliability of input registration in capacitive touch sensor systems.
Implementation Method 1
Capacitive touch sensors (e.g., trackpads, touch screens) may be incorporated into a wide variety of different electronic devices... Capacitive touch sensors may be configured to sense contact from any object that produces a change in electrical charge when contacting the input surface
Implementation Method 2
a stylus configured to transmit a first electrical signal through at least a portion of its exterior surface and into the hand of a user such that the first electrical signal may be sensed by the capacitive touch sensor
Data Source
AI summary
Systems and methods for identifying spurious signals in capacitive touch sensors. In some examples, the technology may include a capacitive touch sensor having an input surface, a stylus configured to transmit a first electrical signal through its exterior surface based on a determination of an orientation of the stylus, and one or more processors configured to: identify a contact to a first area of the input surface based on one or more changes in electrical charge sensed in the first area, determine that the one or more changes in electrical charge sensed in the first area include the first electrical signal, and determine whether to identify the contact to the first area as spurious based on the determination that the one or more changes in electrical charge sensed in the first area include the first electrical signal.