Capacitive Touchscreen ADC Encoding for Low-Power Multi-Touch
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Solution Overview
Problem
Capacitive touchscreen systems face challenges in reducing power consumption and miniaturization, particularly in battery-operated mobile devices, where existing technologies often result in inconclusive multi-touch measurements and high power usage.
Innovation Solution
A capacitive touchscreen system with a grid of electrically conductive drive and sense traces, utilizing mutual capacitance measurements and advanced circuitry for accurate touch detection, including charge acquisition, comparators, AND gates, and analog-to-digital conversion to generate position codes for sensed touches, reducing the number of signals required and enhancing power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If self-capacitance measurement techniques are used with row and column electrode arrangements, then the system can detect touch positions, but multi-touch measurements become inconclusive and require multiple electrodes
Solution Approach 1:
The patent introduces an intermediary encoding scheme during ADC conversion that maps multiple touch positions into distinct digital codes. The weighted sum circuit generates intermediate values that are converted to digital codes, allowing the system to distinguish between multiple simultaneous touches without requiring additional electrodes. This intermediary encoding layer resolves the ambiguity inherent in traditional self-capacitance multi-touch detection.
2Reliability
If traditional capacitive sensing circuitry is used, then touch detection is achieved, but power consumption is high and device size is large
Solution Approach 1:
The patent merges the analog-to-digital conversion process with the touch position encoding process into a single integrated operation. The ADC converter directly converts the weighted sum of analog sensor signals into digital codes that simultaneously represent both the digitized signal values and the encoded touch positions. This consolidation eliminates separate encoding circuitry and reduces overall system power consumption while maintaining detection accuracy.
Solution Approach 2:
The ADC converter is designed to perform multiple functions: it digitizes the analog sensor signals, encodes multiple touch positions, and generates position information all in one operation. This multi-functional approach replaces what would traditionally require separate dedicated circuits for each function, thereby reducing total power consumption and simplifying the device architecture.
3Loss of information
If traditional ADC conversion is used without position encoding, then signal digitization is achieved, but touch position information is lost or requires separate processing
Solution Approach 1:
The patent performs preliminary position encoding during the ADC conversion process itself, before the digital signals undergo further processing. The weighted sum circuit pre-encodes the touch position information into the analog signal values that are then converted to digital codes. This preliminary encoding ensures that position information is preserved in the final digital output without requiring additional processing stages, effectively embedding the position data within the digitization 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
The solution enables accurate multi-touch detection with reduced power consumption and smaller form factor, improving the performance and efficiency of capacitive touchscreen systems in mobile devices by minimizing signal processing and circuit area.
Implementation Method 1
mutual capacitances existing between the first and second pluralities of traces at locations where the first and second pluralities of traces intersect to form pixels, such mutual capacitances changing in the presence of one or more fingers or touch devices brought into proximity thereto
Data Source
AI summary
Disclosed herein are various embodiments of circuits and methods in a capacitive touchscreen system that eliminate the need to digitize an entire array of pixel signals obtained from a touchscreen. Instead, regions of interest, or projections of object or touch signal clusters, from touchscreen 90 are employed to encode the coordinates or positions of objects or touches in an analog-to-digital converter (ADC). Encoding of object positions occurs during digitization of the analog signal clusters, which eliminates the need to separately digitize individual touchscreen signals. The disclosed circuits and methods reduce the number of signal processor channels that might otherwise be required, and lead to power consumption reduction in the capacitive touchscreen system, as well as in reducing the area required to implement the circuit architecture in an integrated circuit.