Guard Electrodes in Capacitive Sensing Stack for Noise Reduction
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Solution Overview
Problem
Existing capacitive sensing devices face challenges in accurately detecting input objects due to capacitively coupled traces on the same layer as sensor electrodes, which introduce noise and errors in sensing signals.
Innovation Solution
A multi-layered capacitive sensing stack is implemented, with a first layer of electrically floating electrodes and a second layer of sensor electrodes, where the floating electrodes are capacitively coupled to the input object and the sensor electrodes, and a guard electrode is used to block unwanted capacitance from affecting the sensing signals, thereby isolating the traces and improving signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traces are routed on the same layer as sensor electrodes, then routing is simplified, but noise and errors in sensing signals increase due to capacitively coupled traces
Solution Approach 1:
The patent divides the sensing structure into multiple layers: sensor electrodes on one layer and traces on another layer. This segmentation separates the functions of sensing and signal routing, allowing traces to be routed effectively while preventing capacitive coupling noise from degrading sensing signal accuracy.
Solution Approach 2:
The patent transitions from a two-dimensional planar arrangement (electrodes and traces on the same layer) to a three-dimensional multi-layer structure. By stacking sensor electrodes and traces on different layers, the patent eliminates capacitive coupling issues while maintaining effective trace routing capability.
2Measurement precision
If a multi-layered structure with floating electrodes is implemented, then sensing accuracy is improved by isolating traces, but device complexity increases
Solution Approach 1:
The patent segments the capacitive sensing device into distinct functional layers: a first layer with sensor electrodes and traces, and a second layer with electrically floating electrodes. This segmentation improves sensing accuracy by isolating traces from capacitive coupling, while the modular layered structure makes the complexity manageable through clear functional separation.
Solution Approach 2:
The electrically floating electrodes act as an intermediary between the sensor electrodes and the external environment. These floating electrodes capacitively couple to input objects while being electrically isolated, thereby mediating the sensing function and blocking unwanted capacitance from affecting the sensing signals on the trace layer.
3Measurement precision
If guard electrode is added to block unwanted capacitance, then sensing signal accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The guard electrode is implemented as a distinct element on the first layer, separate from both the sensor electrodes and the traces. This segmentation allows the guard electrode to specifically target and block unwanted capacitance from adjacent traces without interfering with the primary sensing function, improving signal accuracy while maintaining manufacturing feasibility through clear spatial separation.
Solution Approach 2:
The guard electrode converts the potentially harmful effect of capacitive coupling from traces into a beneficial shielding effect. By strategically positioning the guard electrode between the traces and sensor electrodes, the structure that would normally introduce noise is instead used to block unwanted capacitance, thereby improving sensing signal accuracy.
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 enhances the accuracy of capacitive sensing by mitigating noise and errors, allowing for precise detection of input objects without compromising the ability to route traces effectively, thus improving the overall performance of the input device.
Implementation Method 1
a guard electrode at least partially overlaps one of the routing traces in the sensing stack... configured to drive sensing signals onto the routing traces for performing capacitive sensing
Implementation Method 2
each of the electrically floating electrodes at least partially overlaps a corresponding one of the sensor electrodes in the sensing stack... capacitively coupled to the input object and the sensor electrodes
Data Source
AI summary
This disclosure generally provides an input device that includes a multi-layered capacitive sensor which includes a first layer disposed over a second layer that contains a plurality of sensor electrodes coupled to respective traces. The first and second layers form a capacitive sensing stack where the first layer is between the second layer and a touch surface for interacting with the input object. The first and second layers may be disposed on either the same substrate or different substrates in the stack. In one embodiment, the first layer includes electrically floating electrodes and at least one guard electrode. These components may align with respective components in the second layer. For example, the electrically floating electrodes in the first layer may at least partially cover the sensor electrodes in the second layer.