Differential Charge Converter Circuit for Touch Screen Noise Rejection
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Solution Overview
Problem
As touch sensitive displays become thinner, they experience increased parasitic capacitances that couple display noise to the sensing layer, degrading the accuracy of touch sensing due to existing methods' inability to effectively reject noise.
Innovation Solution
A differential charge converter circuit is used, with capacitive couplings between transistors and sense lines during a reset period, decoupling from voltage references during a scan period to reject display noise by cross-coupling noise to the gates and sources of capacitively cross-coupled transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If touch sensitive displays are made thinner to meet consumer demands, then device thickness is reduced, but parasitic capacitances increase causing display noise to couple through to the sensing layer
Solution Approach 1:
The patent applies differential sensing that intentionally exploits the coupled display noise by capacitively cross-coupling it to the gates and sources of cross-coupled transistors. This converts the harmful noise coupling into a beneficial common-mode signal that is then rejected through the differential measurement process, thereby improving noise rejection while maintaining thin display design
Solution Approach 2:
The patent changes the operational parameters of the charge converter circuit by implementing capacitive cross-coupling during the reset period and decoupling during the scan period. This dynamic parameter change allows the circuit to optimize noise rejection at different operational phases, effectively reducing display noise coupling while maintaining thin display structure
2Object-affected harmful factors
If existing noise reduction methods are used, then some noise is reduced, but an undesirable amount of display noise still couples through to the sensing layer
Solution Approach 1:
Instead of merely attempting to block or reduce noise coupling, the patent converts the harmful noise into a useful common-mode signal through capacitive cross-coupling. The differential sensing architecture then naturally rejects this common-mode noise, achieving superior noise rejection and touch sensing accuracy compared to conventional methods
Solution Approach 2:
The patent implements a feedback mechanism where the capacitive cross-coupling during the reset period intentionally feeds the display noise back to the transistor gates and sources. This feedback creates a common-mode signal that is subsequently rejected by the differential sensing circuit, thereby improving measurement precision
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 effectively reduces display noise, enhancing the accuracy and performance of touch sensing by isolating common mode noise and boosting transconductance, improving noise rejection beyond existing techniques.
Implementation Method 1
The display noise is capacitively coupled from the display layer to each of the plurality of sense lines of the sensing layer
Data Source
AI summary
Disclosed herein is an electronic device including a display layer generating display noise based on scanning thereof and a sensing layer including a plurality of sense lines. The display noise is capacitively coupled from the display layer to each of the plurality of sense lines of the sensing layer. A differential charge converter circuit has first and second differential inputs respectively coupled to corresponding ones of the plurality of sense lines, and first and second reference inputs. The first and second reference inputs of the differential charge converter circuit are coupled to voltage references during a reset period, and are decoupled from the voltage references during a scan period.