Capacitive Touch Sensing with Voltage Divider Column Addressing
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Solution Overview
Problem
Capacitive sensing systems for mobile devices face challenges with limited space, increased complexity, and higher costs due to the need for multiple buttons and scanning channels, especially with larger touch areas, which affects aesthetics and market competitiveness.
Innovation Solution
A capacitive touch sensing device with a logical array of buttons arranged in rows and columns, utilizing a first and second node for transmit voltages and intermediate nodes with different voltages applied, reducing the number of required pins and internal circuitry by using a resistor divider to divide the voltage across columns, allowing for efficient detection of button touches without separate transmit pins for each column.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If separate transmit pins are used for each column in a capacitive sensing array, then the precision of capacitance measurement is improved, but the device complexity and number of required pins increases significantly
Solution Approach 1:
The patent merges multiple transmit pin functions into a single transmit pin by using a voltage divider network. Instead of requiring separate transmit pins for each column, the voltage divider allows one pin to provide differentiated voltages to multiple columns through resistive division, thereby reducing pin count while maintaining the ability to address and measure each column individually
Solution Approach 2:
The voltage divider network acts as an intermediary between the single transmit pin and the multiple column electrodes. The resistors in the voltage divider serve as mediator elements that distribute and differentiate the transmit voltage to various columns, enabling indirect control and measurement of each column without requiring direct separate pin connections
2Area of stationary object
If the number of buttons in the sensing array is increased to cover larger touch areas, then the sensing coverage area is improved, but the quantity of required scanning channels and hardware components increases
Solution Approach 1:
The patent implements multi-functionality by enabling a single transmit pin to serve multiple columns through the voltage divider network. This universal approach allows the same hardware component (transmit pin) to perform multiple functions (driving and measuring multiple columns), thereby supporting larger sensing arrays without proportionally increasing the number of required hardware components
Solution Approach 2:
The patent introduces a voltage dimension to differentiate between columns instead of using separate physical pin connections for each column. By varying the voltage levels through the resistor divider network, the system can address and measure multiple columns along the voltage dimension, effectively mapping spatial column relationships to voltage level relationships
3Productivity
If more scanning channels are added to support larger touch areas, then the productivity of touch detection is improved, but the device complexity and manufacturing cost increases
Solution Approach 1:
The patent combines multiple scanning channel functions into a single physical channel by using the voltage divider network. Instead of requiring separate dedicated scanning circuits for each column, the combined approach allows one scanning channel to sequentially or simultaneously measure multiple columns through voltage differentiation, reducing overall hardware complexity and manufacturing cost
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 enables efficient detection of multiple touches across a larger number of buttons with reduced hardware requirements, minimizing space and cost while maintaining sensitivity and accuracy, thereby improving the design of capacitive sensing systems for mobile devices.
Implementation Method 1
the sensing detects a change in capacitance, in response to a human or other material (organic or inorganic) in contact or proximity with the sensor
Implementation Method 2
change in capacitance can be detected resulting from a received signal measured at one capacitor plate, in response to a transmitted signal at the other capacitor plate
Data Source
AI summary
A capacitive touch sensing device, with: (i) a logical array of capacitive buttons have a number R of rows and a number C of columns; (ii) a first node coupled to a first column in the number C of columns, the first node for receiving a first transmit voltage; (iii) a second node coupled to a second column in the number C of columns, the second node for receiving a second transmit voltage; (iv) a number of intermediate nodes between the first node and the second node, wherein each intermediate node is coupled to a respective column in the number C of columns; and (v) circuitry for applying a respective different voltage to each of the intermediate nodes in response to the first transmit voltage and the second transmit voltage.