Touch Screen Shield Wiring Layout for Parasitic Capacitance Reduction
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Solution Overview
Problem
Projected-capacitive touch screens face challenges in differentiating capacitance offsets from physical quantity-induced changes, leading to errors in detecting physical quantities due to parasitic capacitance formed between outer lead wiring and display elements.
Innovation Solution
A touch screen design incorporating a plurality of sensor wirings, lead wirings, a first shield wiring, and capacitors with a larger interval between the outermost lead wiring and the shield wiring, along with capacitors connected to the sensor wirings, to reduce capacitance variations and parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If outer lead wiring is provided to connect sensor wirings to external circuits, then electrical connectivity is achieved, but parasitic capacitance is formed between the outer lead wiring and display elements, causing capacitance offset variations
Solution Approach 1:
A shield wiring is introduced as an intermediary component between the outer lead wiring and the display elements. This shield wiring acts as a mediator that blocks or reduces the parasitic capacitance coupling between the lead wiring and display elements, thereby maintaining electrical connectivity while improving capacitance detection accuracy
Solution Approach 2:
The parasitic capacitance effect, which initially causes measurement errors, is converted into a beneficial shielding effect. By strategically positioning the shield wiring to overlap with the outer lead wiring, the harmful parasitic capacitance is transformed into a protective shielding mechanism that reduces unwanted electrical coupling
2Measurement precision
If shield wiring is added to reduce parasitic capacitance, then capacitance detection accuracy is improved, but device complexity increases
Solution Approach 1:
The shield wiring is merged with the existing outer lead wiring structure by positioning them to overlap in the plan view. This merging approach allows the shield wiring to perform its capacitance-reducing function while sharing the same spatial pathway as the lead wiring, thereby minimizing the increase in device complexity
Solution Approach 2:
The shield wiring serves multiple functions: it provides electromagnetic shielding to reduce parasitic capacitance, maintains electrical isolation between different wiring layers, and integrates with the existing lead wiring structure. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity
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 design effectively reduces capacitance variations and parasitic capacitance, enhancing the accuracy of physical quantity detection by minimizing capacitance-to-ground deviations and improving detection sensitivity.
Implementation Method 1
a capacitor (92 to 96), each comprising a first electrode (R2a to R6a) and a second electrode (42a to 46a) which are apart from each other and are connected to the end portions of the column-direction wirings (21)
Data Source
AI summary
A touch screen includes a first shield wiring surrounding a plurality of sensor wirings and a plurality of lead wirings, and capacitors. The distance between the first shield wiring and the outermost lead wiring which is the outermost wiring, out of the plurality of lead wirings, is larger than the intervals between the plurality of lead wirings. The capacitors are constituted by first and second electrodes including extending portions which extend in the extending direction.