Capacitance Module Shield Layout for Touch and RF Isolation
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Solution Overview
Problem
Capacitive touch pads on processor-based devices often interfere with radio frequency transmissions due to electrical shielding, requiring difficult antenna tuning and increased power consumption, and are challenging to manufacture due to variations in the touch pad PCB affecting antenna resonance.
Innovation Solution
A stack of layers with a capacitive sensor layer, electrodes, and an antenna, where a shield feature, such as a ground ring, is placed between the electrodes and the antenna to reduce interference, allowing the capacitive sensor and antenna to operate independently without overlapping with the electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical shielding is placed near the radio frequency antenna to prevent noise interference, then touch pad functionality is improved, but radio frequency transmission and reception are blocked
Solution Approach 1:
The shield feature is divided into multiple sections rather than being a continuous structure. These segmented shield sections are positioned between the antenna and touch pad electrodes, providing noise protection while allowing radio frequency signals to pass through the gaps between sections.
Solution Approach 2:
A dielectric material is introduced as an intermediary between the shield feature and the antenna. This dielectric layer allows radio frequency signals to pass through while maintaining the shielding effect on electrical noise, effectively mediating between the conflicting requirements of noise protection and signal transmission.
2Object-affected harmful factors
If the antenna is placed near the touch pad to allow radio frequencies through shielding, then radio frequency transmission is improved, but antenna tuning becomes difficult and power consumption increases
Solution Approach 1:
The shielding function is extracted from the traditional location near the antenna and repositioned to a separate shield feature located between the antenna and touch pad electrodes. This extraction allows the antenna to operate independently without being constrained by nearby shielding structures, simplifying tuning and reducing power consumption.
Solution Approach 2:
The shielding approach transitions from a two-dimensional planar shield near the antenna to a multi-layered three-dimensional structure with dielectric materials and segmented shield sections positioned at different heights and locations, enabling effective noise protection without interfering with antenna radiation patterns.
3Object-affected harmful factors
If the antenna is placed near the touch pad electrodes, then radio frequency transmission is enabled, but manufacturing becomes difficult due to PCB variations affecting antenna resonance
Solution Approach 1:
The shield feature is designed with locally optimized properties, including segmented sections with specific geometries and dielectric materials positioned at specific locations between the antenna and electrodes. This localized shielding approach provides effective noise protection while being insensitive to overall PCB manufacturing variations, improving manufacturing consistency.
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 configuration enables efficient radio frequency transmission and reception while maintaining touch pad functionality, reducing manufacturing complexity and power consumption by isolating the capacitive sensor from the antenna's interference.
Implementation Method 1
capacitive touch pads often require electrical shielding to prevent noise from the processor-based device from interfering with normal touch pad functions
Implementation Method 2
processor-based devices often include radio frequency (e.g., 3 MHz-30 GHz) transmitters, receivers, transceivers
Data Source
AI summary
An apparatus may include a substrate including a capacitance sensing electrode, an antenna on the substrate, and a shield feature between the electrodes and the antenna.