Shared Sigma-Delta Capacitance Sensing With Fewer Pins
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Solution Overview
Problem
Current capacitance sensors face challenges in improving performance without increasing costs, pin count, electrode routing, component count, size, or complexity, while also needing a design that is flexible and cost-effective for various electronic device implementations.
Innovation Solution
The use of sigma-delta charge transfer techniques that allow for the detection of measurable capacitance using standard microcontrollers, with components such as passive networks, voltage conditioning circuits, and guarding electrodes shared between multiple sensing channels to reduce device complexity and improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional capacitance sensing methods are used with dedicated components for each sensing channel, then measurement precision is maintained, but device complexity and component count increase
Solution Approach 1:
The patent merges multiple sensing channels to share a common integrating capacitor and passive network. Specifically, multiple capacitance sensors connect through switches to a shared integrating capacitor, allowing charge accumulation from multiple channels using a single component instead of requiring dedicated capacitors for each channel. This reduces component count and device complexity while maintaining measurement precision through the charge transfer technique.
Solution Approach 2:
The integrating capacitor serves multiple functions: it accumulates charge from multiple different sensing channels sequentially, acts as a charge storage element for the sigma-delta modulation process, and enables universal measurement of different capacitance values. This multi-functional design eliminates the need for dedicated capacitors for each sensing channel, reducing overall device complexity.
2Measurement precision
If more components are added to improve capacitance sensing performance, then measurement precision improves, but device complexity and costs increase
Solution Approach 1:
The patent combines multiple sensing channels to share a common integrating capacitor and passive network. Instead of using separate capacitors and associated components for each channel, the design merges these resources so that a single integrating capacitor serves multiple channels through sequential charge transfer operations, thereby reducing component count while maintaining precision.
Solution Approach 2:
The patent replaces traditional voltage-based capacitance measurement methods with a charge transfer technique. Instead of directly measuring voltage across capacitors, the system transfers charge packets between capacitors and uses sigma-delta modulation to encode capacitance values. This substitution enables high-precision measurement with fewer components by using charge quantity rather than voltage level as the measurement parameter.
3Measurement precision
If dedicated integrating capacitors are used for each sensing channel, then measurement precision is maintained, but pin count and device complexity increase
Solution Approach 1:
The patent merges multiple sensing channels to share a common integrating capacitor. Instead of allocating a dedicated integrating capacitor to each channel (which would require multiple capacitor pins and associated routing), the design uses a single shared integrating capacitor that is sequentially connected to different sensing channels through switches, reducing pin count and simplifying device architecture.
Solution Approach 2:
The patent introduces dynamic switching between sensing channels and the shared integrating capacitor. The switches dynamically connect different sensing channels to the common integrating capacitor at different time intervals, enabling sequential charge transfer from multiple channels to a single capacitor. This dynamic multiplexing approach allows one capacitor to serve multiple channels, reducing the total number of capacitors and associated pins required.
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 approach enables efficient and accurate capacitance sensing, reducing device complexity and costs, while maintaining flexibility and effectiveness across different implementations, such as in proximity sensor devices for detecting finger or stylus positions.
Implementation Method 1
a measurable capacitance is allowed to share charge with a passive network so that the passive network accumulates charge on at least one integrating capacitance
Data Source
AI summary
Methods, systems and devices are described for detecting a measurable capacitance using sigma-delta charge transfer techniques that can be implemented with many standard microcontrollers, and can share components to reduce device complexity and improve performance. In the various implementations of this embodiment, the passive network used to accumulate charge can be shared between multiple measurable capacitances. A switch or IO controlling the charge sharing and/or charge changing can also be shared Likewise, in various implementations a voltage conditioning circuit configured to provide a variable reference voltage can be shared between multiple measurable capacitances. Finally, in various implementations a guarding electrode configured to guard the measurable capacitances can be shared between multiple measurable capacitances. In each of these cases, sharing components can reduce device complexity and improve performance.