Capacitive Touch Sensor IO Pin Reduction via Diode Multiplexing
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Solution Overview
Problem
Capacitive touch sensors in mobile devices require a large number of input/output (IO) pins, which occupy valuable space and increase complexity as the number of buttons or touch points increases, limiting the ability to achieve higher resolution and precise touch sensitivity.
Innovation Solution
A capacitive touch sensor system that reduces the number of IO pins needed by using a grid of intersecting sensor lines and diodes to multipurpose IO pins for both transmitting and receiving signals, allowing fewer pins to operate a touch sensor with the same or higher resolution as conventional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitive touch sensors use separate transmit and receive sensor lines for each button, then touch detection accuracy is maintained, but the number of IO pins increases significantly
Solution Approach 1:
Each IO pin is configured to perform both transmit and receive functions by dynamically switching roles. The sensor lines connected to the same IO pin can alternate between being transmit lines and receive lines based on the scanning phase, allowing a single IO pin to handle multiple functions that traditionally required separate pins.
Solution Approach 2:
The system dynamically switches the functional role of sensor lines between transmit and receive modes during operation. By sequentially changing which lines are active for transmission and which are active for reception, the system optimizes pin utilization and reduces the total number of IO pins required.
2Measurement precision
If the number of buttons or touch points increases to achieve higher resolution, then touch sensitivity improves, but the number of IO pins required increases
Solution Approach 1:
IO pins are reused across multiple buttons and touch points by switching their transmit/receive roles. A single IO pin can sequentially serve multiple sensor lines that connect to different buttons, enabling high-resolution touch detection without proportionally increasing the number of physical pins.
Solution Approach 2:
The system uses periodic scanning where IO pins cycle through different functional states. By systematically alternating between transmit and receive phases across multiple scanning cycles, the system can monitor numerous touch points using a reduced set of physical pins.
3Adaptability or versatility
If more IO pins are used to support more buttons, then button count increases, but physical space occupation increases
Solution Approach 1:
The same physical IO pins are shared across multiple buttons through role switching. This allows the system to support a larger number of buttons without adding proportional physical space for additional pins, as each pin serves multiple buttons at different times in the scanning sequence.
4Reliability
If separate transmit and receive lines are used for each button, then signal interference is reduced, but the system complexity increases
Solution Approach 1:
The system dynamically assigns transmit and receive functions to different sensor lines during sequential scanning phases. By temporally separating transmit and receive operations on the same physical lines and using diodes to prevent backward signal flow, the system maintains signal quality while reducing structural complexity.
Solution Approach 2:
Diodes are introduced as intermediary components to control signal direction. These diodes prevent signal backflow and ensure that transmit signals do not interfere with receive operations, enabling the reuse of sensor lines for both functions without compromising signal integrity.
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 enables the operation of touch sensors with fewer IO pins, allowing for more buttons or higher resolution with the same number of pins, reducing physical space occupation and enhancing touch sensitivity and complexity management.
Implementation Method 1
for each IO pin, a diode that is configured to couple to one of the first or second sensor lines
Implementation Method 2
each intersection includes a capacitor coupling together the intersecting sensor lines
Data Source
AI summary
A touch sensor apparatus includes a grid of intersecting sensor lines, a plurality of input/output (IO) pins, a plurality of diodes, a processor coupled to the IO pins. More specifically, each intersection includes a capacitor coupling together the intersecting sensor lines. Each diode is coupled to a corresponding IO pin, wherein each IO pin couples through its corresponding diode to a channel of intersection points of the sensor lines and, without the diode, each IO pin couples to a different channel of intersecting points of the sensor lines. The processor is configured to sequentially provide a transmit signal through each IO pin while detecting a response signal on the other IO pins.