Sensor Panel Autocalibration via Stimulus Amplitude Variation
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Solution Overview
Problem
Sensor panels in touch screens exhibit inconsistent analog channel output values due to variations in electrical characteristics caused by processing variations, manufacturing tolerances, assembly differences, aging, stress, dirt, moisture, deformation, and temperature, leading to inconsistent or false triggering of virtual buttons.
Innovation Solution
The solution involves calibrating sensor panels by simulating a full-touch condition and adjusting the amplitude of the input stimulus to match a baseline condition, allowing for consistent analog channel outputs across the panel, which is achieved by measuring and storing a lowered stimulus amplitude (Vstim_cal) to emulate a full-touch condition and tuning the analog channels during field calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sensor panels are manufactured with standard tolerances, then manufacturing cost and complexity are reduced, but analog channel output values vary due to processing variations, manufacturing tolerances, and assembly differences
Solution Approach 1:
The system performs preliminary calibration measurements during manufacturing to establish baseline analog channel output values for each pixel. These baseline values are stored and used to calculate per-pixel calibration factors that compensate for manufacturing variations. This preliminary action eliminates the need for complex real-time calibration systems while ensuring consistent touch recognition across all pixels.
Solution Approach 2:
The system changes the stimulus amplitude parameter to emulate full-touch conditions during calibration measurements. By varying the stimulus level and observing the analog channel responses, the system determines optimal calibration factors for each pixel. This parameter change approach allows the system to account for non-linear sensor behavior and establish accurate reference points for touch detection.
2Reliability
If per-pixel calibration is performed to account for sensor variations, then touch recognition consistency is improved, but calibration time and processing complexity increase
Solution Approach 1:
All per-pixel calibration measurements are performed during the manufacturing process before the sensor panel is deployed. The calibration factors are calculated and stored in non-volatile memory, allowing the sensor panel to operate with consistent touch recognition without requiring additional calibration time during field use. This preliminary calibration approach eliminates ongoing calibration time requirements.
Solution Approach 2:
The sensor panel performs its own calibration measurements autonomously during manufacturing using integrated test fixtures. Each pixel self-calibrates by measuring its analog channel output response to standardized stimuli, eliminating the need for manual calibration procedures. This self-service approach significantly reduces calibration time and complexity compared to manual methods.
3Measurement precision
If stimulus amplitude is varied to emulate full-touch conditions, then calibration accuracy is improved, but measurement complexity increases
Solution Approach 1:
The system varies the stimulus amplitude parameter to different predefined levels (e.g., nominal, reduced) to emulate different touch conditions. By measuring analog channel responses at multiple stimulus levels, the system accurately characterizes pixel behavior under full-touch conditions without requiring complex mechanical test fixtures. This parameter-based approach simplifies the measurement system while improving calibration accuracy.
Solution Approach 2:
Instead of physically applying full-touch pressure during calibration, the system creates an electrical copy of the full-touch condition by adjusting the stimulus amplitude to produce equivalent analog channel output responses. This electrical copying approach eliminates the need for complex mechanical test fixtures while achieving the same calibration objectives with simpler measurement equipment.
Data Source
AI summary
The automatic calibration of a sensor panel is disclosed by varying the amplitude of an input stimulus Vstim to simulate a full-touch condition and calibrating each pixel of the sensor panel in accordance with the difference between the simulated full-touch condition and a baseline full-touch condition. To accomplish this, a baseline full scale output FS_targ_cal can be measured at during pre-delivery calibration for each pixel using a test fixture capable of applying a no-touch to full-touch condition given a nominal Vstim. A full-touch condition can then be emulated for each pixel by lowering Vstim until the current full scale output FS_targ_current equals FS_targ_cal, and determining the Vstim value Vstim_cal at that point. During field calibration, Vstim_cal can be applied to each pixel to simulate a full-touch condition, and FS_targ_current can be obtained and compared against FS_targ_cal. Each analog channel can then be tuned so that in subsequent full-touch conditions, FS_targ_current will approximately equal FS_targ_cal.