Touch Sensing Apparatus Using Code-Division Multiplexing
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Solution Overview
Problem
Existing touch-sensitive panels face challenges in accurately determining the location of objects on a touch surface, particularly with increasing surface area and spatial resolution, as they require a large number of optical emitters and receivers, leading to high cost and complexity, and suffer from reduced temporal resolution and signal-to-noise ratio when attempting multi-touch detection.
Innovation Solution
A touch sensing apparatus that uses a group of emitters to emit light with unique codes, allowing a processing element to distinguish and separate light from individual emitters, enabling simultaneous activation of multiple emitters and improved temporal resolution by using a light transmissive element and detectors to determine object positions through image reconstruction algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If sequential activation of emitters is used to reduce the number of emitters and receivers, then the number of components is reduced, but temporal resolution deteriorates
Solution Approach 1:
The patent applies periodic action by using time-multiplexed activation of emitters in sequential groups during different time intervals within a frame period. Each emitter or group of emitters is activated periodically at specific time slots, allowing the system to maintain reduced component count while achieving acceptable temporal resolution through temporal segmentation of the detection process.
Solution Approach 2:
The patent segments the emitter activation process into multiple groups that operate in different time intervals. Instead of activating all emitters simultaneously or using a single sequential emitter, the system divides emitters into segments that are activated in a time-multiplexed manner, allowing parallel processing of different spatial zones while maintaining reduced hardware requirements.
2Speed
If shortened activation time for each emitter is used to increase temporal resolution, then temporal resolution is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The patent merges multiple emitters into groups that are activated simultaneously within the same time interval. By combining the light output from multiple emitters that illuminate different spatial zones, the system maintains short activation times for temporal resolution while increasing the total light signal received, thereby improving the signal-to-noise ratio through constructive signal combination.
Solution Approach 2:
The patent ensures continuity of useful action by overlapping the activation intervals of different emitter groups within a frame period. This allows the detection process to continue seamlessly across different spatial zones without idle gaps, maintaining high temporal resolution while ensuring each emitter group has sufficient activation time to generate adequate signal strength.
3Measurement precision
If a large number of emitters and receivers are used to increase surface area and spatial resolution, then spatial resolution is improved, but device complexity and cost increase
Solution Approach 1:
The patent transitions from a spatial arrangement of multiple emitters and receivers to a temporal arrangement where fewer emitters are activated in different time slots. By adding the time dimension to the detection process, the system achieves the same spatial resolution with fewer physical components, effectively trading spatial complexity for temporal processing.
Solution Approach 2:
The patent makes each emitter serve multiple functions by activating different emitters for different spatial zones at different times. Each emitter acts as a universal light source that can illuminate any spatial zone when activated at its designated time interval, eliminating the need for dedicated emitters for each spatial position and reducing the total component count.
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 allows for accurate detection of object locations irrespective of object shape, reduces the number of emitters and receivers needed, and enhances temporal resolution and signal-to-noise ratio, enabling efficient multi-touch detection while maintaining high spatial resolution.
Implementation Method 1
a group of emitters arranged to emit light to illuminate at least part of the touch surface
Implementation Method 2
a light detector arranged to receive light from the group of emitters
Data Source
AI summary
A touch sensing apparatus includes a group of emitters arranged to emit light to illuminate at least part of the touch surface, a light detector arranged to receive light from the group of emitters, and a processing element. Each emitter is controlled to transmit a code by way of the emitted light such that the code identifies the respective emitter. The codes may at least partly be transmitted concurrently. The codes may be selected such that a value of an autocorrelation of each code is significantly higher than a value of a cross-correlation between any two codes of different emitters. The processing element processes an output signal from the light detector to separate the light received from the individual emitters based on the transmitted codes, and to determine the position of the object/objects based on the light received from the individual emitters.