Capacitive Touch Sensing Code Word Segmentation for Fast Position Estimation
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Solution Overview
Problem
Capacitive touch sensing devices using code-division multiplexing (CDM) face challenges in estimating touch positions before receiving full receive signals, which is crucial for applications with fast output report rates such as human interface devices.
Innovation Solution
A method and system that utilize a spread-spectrum technique to estimate touch positions by assigning code words with first and second code word portions to transmit electrodes, decoding partial receive signals, and computing touch position estimates based on these decoded portions, allowing for touch position estimation before full receive signals are received.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If code-division multiplexing is used to transmit signals from multiple transmit electrodes through a shared channel, then signal multiplexing capability is improved, but touch position estimation cannot be performed before full receive signals are received
Solution Approach 1:
The patent segments the code word into multiple portions (e.g., first portion and second portion) and processes them separately. The receiver decodes the first portion of the receive signal using the first portion of the code word to generate an initial touch position estimate, then later refines this estimate using the second portion. This segmentation allows partial processing and early estimation without waiting for the complete signal.
Solution Approach 2:
The patent performs preliminary touch position estimation using only the first portion of the received signal and the corresponding first portion of the code word. This preliminary estimate is generated before the full receive signal is received, allowing the system to provide early touch position information. The estimation is later refined when the second portion becomes available, but the preliminary action enables faster initial response.
2Measurement precision
If full code words are transmitted to ensure accurate signal identification, then signal decoding accuracy is improved, but report rate for touch position estimates decreases
Solution Approach 1:
The patent applies partial action by using only a portion (e.g., first 50%) of the code word for initial touch position estimation. This partial processing enables the system to generate reportable touch position estimates without waiting for the complete code word to be received and processed, thereby increasing the report rate. The full code word is still transmitted for refined estimation when needed.
Solution Approach 2:
The patent segments the code word processing into multiple stages: first decoding the first portion to generate an initial estimate, then optionally refining with the second portion. This segmentation allows the system to provide frequent updates based on partial data while maintaining the option for higher accuracy when complete data is available, thus increasing overall productivity.
3Area of stationary object
If code words are assigned to all transmit electrodes for complete coverage, then touch detection coverage is improved, but processing complexity increases
Solution Approach 1:
The patent segments the set of transmit electrodes into multiple subsets, with different code words assigned to different subsets. This segmentation allows the receiver to process signals from different subsets separately and independently, reducing the overall processing complexity while maintaining complete coverage across all electrodes.
Solution Approach 2:
The patent applies partial action by initially processing only a subset of code words (e.g., first subset assigned to first subset of transmit electrodes) to generate touch position estimates. This reduces the immediate processing burden while still providing comprehensive coverage over time as different subsets are processed in sequence or parallel.
Data Source
AI summary
Systems having a capacitive touch sensing system with transmit and receive electrodes positioned to have mutual capacitances at node intersections that deviate when a node is touched; a processor; and a machine readable storage medium with instructions to: assign complete code words to transmit electrodes; identify a subset of transmit electrodes based on a prior touch position estimate; generate a transmit signal for the transmit electrodes; receive a first portion of a receive signal for receive electrodes indicative of capacitances; decode the first portion of the receive signal of receive electrodes using the first portions of the code words; and compute touch position estimates for the subset of transmit electrodes based on the decoded first portions of the receive signals.