Touch Screen ADC Reference Voltage Management
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Solution Overview
Problem
Resistive touch screen panels face issues with power dissipation and noise immunity, particularly when integrated with LCDs, and suffer from reduced clarity and vulnerability to damage from sharp objects.
Innovation Solution
A touch screen digitizing system incorporating an analog to digital converter with dynamically coupled reference terminals, utilizing MOS transistors and sample and hold circuits to manage power dissipation and noise immunity, and featuring resistive sheets with orthogonal axes for precise touch detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If resistive touch screen panels are used, then affordability and resistance to external elements are improved, but clarity is reduced and the layer can be damaged by sharp objects
Solution Approach 1:
The touch screen panel is divided into multiple resistive layers (first resistive layer, second resistive layer, third resistive layer) with different properties. The first and second resistive layers form the traditional resistive touch interface, while the third resistive layer is integrated with the liquid crystal display structure. This segmentation allows each layer to serve specific functions: the first two layers provide touch sensitivity and durability, while the third layer maintains display clarity and prevents damage from sharp objects.
2Stability of the object's composition
If continuous reference voltages are supplied to the ADC, then measurement stability is improved, but power dissipation increases
Solution Approach 1:
The reference voltages for the ADC are supplied periodically rather than continuously. Reference voltages are provided during sampling phases when touch coordinate measurement is required, and removed during conversion phases. This periodic supply maintains measurement stability when needed while significantly reducing power dissipation during non-measurement periods, achieving an optimal balance between stability and energy efficiency.
3Stability of the object's composition
If reference terminals are continuously coupled to reference voltages, then ADC operation stability is improved, but noise from LCD operation affects measurement accuracy
Solution Approach 1:
Reference voltages are supplied periodically during sampling phases when touch coordinate measurement is required, and removed during conversion phases when the ADC is performing its conversion operation. This timing separation ensures that the ADC operation is not affected by noise from LCD operation, while still maintaining measurement stability during the sampling phase when touch detection is needed.
4Reliability
If multiple resistive layers are integrated with LCD, then durability and clarity are improved, but device complexity increases
Solution Approach 1:
The third resistive layer is merged with the liquid crystal display structure, combining the touch sensing function with the display function into a single integrated component. This merging approach provides durability and clarity improvements while minimizing the increase in device complexity, as the third resistive layer shares the same structural space and control mechanisms as the LCD structure itself.
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 reduces power dissipation and enhances noise immunity from LCD operation while maintaining clarity and durability by dynamically managing reference voltages during sampling and conversion phases.
Implementation Method 1
A resistive touch screen panel is coated with a thin metallic electrically conductive and resistive layer that causes a change in the electrical current which is registered as a touch event
Implementation Method 2
The analog to digital converter has a first input, a first reference terminal, a second reference terminal, and an output terminal. The first input is coupled to the third terminal when the first resistive sheet is energized and the second resistive sheet is not, and coupled to the first terminal when the second resistive sheet is energized and the first resistive sheet is not.
Data Source
AI summary
A touch screen digitizing system comprising a touch screen unit and an analog to digital converter. The touch screen unit includes a first resistive sheet with opposing first and second terminals and a second resistive sheet with opposing third and fourth terminals. The first and second resistive sheets are alternatively energized through the first, second, third, and fourth terminals. The analog to digital converter has an input coupled to the third terminal when the first resistive sheet is energized and the second resistive sheet is not, and coupled to the first terminal when the second resistive sheet is energized and the first resistive sheet is not, a first reference terminal dynamically coupled to a first reference voltage, a second reference terminal dynamically coupled to the second reference voltage, and an output terminal providing digital output data.