Self-Capacitor Sensing AC-Mode Bridge Global Current Rotation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Modern touchscreen displays face increasing challenges in reducing noise coupling in capacitive touch-sensing layers, particularly for self-capacitor sensing, which involves smaller signal levels and is less sensitive due to larger display sizes, making it difficult to reliably sense small changes in capacitance.
Innovation Solution
A multi-branch AC-mode bridge approach with global current rotation is employed for self-capacitor sensing, utilizing K branches and adjustable current sources to generate sinusoidal input currents, a unit current rotator for rotating these currents, and an error amplifier to generate an error signal, allowing for concurrent differential readout of touch sense channels and mitigating display noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If self-capacitor sensing is used in large display sizes, then the display area increases, but the sensing sensitivity decreases due to smaller signal levels
Solution Approach 1:
The sensing system is divided into multiple independent sensing channels, each with its own signal path and processing. This segmentation allows each channel to be optimized for sensitivity while the overall system achieves large display coverage, resolving the contradiction between display area and sensing sensitivity.
Solution Approach 2:
An intermediary signal processing stage is introduced between the capacitive sensing elements and the readout circuitry. This intermediary stage amplifies and conditions the small signal levels from self-capacitors, enabling reliable detection even in large displays where signal levels are inherently small.
2Area of stationary object
If display size increases, then the display area increases, but the display noise coupling increases making sensing more challenging
Solution Approach 1:
The harmful display noise is extracted and separated from the useful sensing signal through dedicated noise cancellation circuitry. By taking out the noise component specifically, the system can maintain large display area while preventing noise from degrading sensing performance.
Solution Approach 2:
A feedback mechanism is implemented where the display noise is continuously monitored and fed back to the sensing circuitry. This feedback allows real-time cancellation of noise coupling, enabling the system to handle larger display areas without being overwhelmed by increased noise levels.
3Device complexity
If conventional sensing circuits are used for small capacitance changes, then the circuit design is simpler, but the measurement precision is insufficient
Solution Approach 1:
The sensing circuit employs dynamic signal processing techniques, including time-varying impedance matching and adaptive amplification. These dynamic elements improve measurement precision for small capacitance changes while keeping the overall circuit design manageable through systematic approaches.
Solution Approach 2:
The circuit operates by changing key parameters such as frequency, impedance, and gain dynamically during the sensing process. These parameter changes enable the circuit to detect very small capacitance variations with high precision without requiring excessively complex circuit architecture.
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 enhances the sensitivity and performance of self-capacitor sensing, enabling reliable detection of touch events without the need for synchronization with display control signals, supporting higher noise scenarios and non-synchronized modes of operation.
Implementation Method 1
A unit current rotator rotates the K sinusoidal input currents to each of the K branches, so that each branch current is formed by a rotating contribution from each of the sinusoidal input currents
Implementation Method 2
K nominally identical current sources generate K nominally identical sinusoidal input currents based on an error signal, and the error signal is generated based on comparing a sinusoidal driver signal with feedback from one or more of the K branches
Implementation Method 3
Each channel has a respective channel self-capacitance (Ci) that includes a respective base self-capacitance (Cs) corresponding to display noise capacitively coupled onto the channel from the display panel
Data Source
AI summary
Techniques are described for using a multi-branch AC-mode bridge approach with global current rotation for self-capacitor sensing in a capacitive touch panel, such as integrated into a display of a touchscreen electronic device. K channels are coupled with K branches of a multi-branch AC-mode bridge to form K−1 pairs of channels for concurrent differential readout. K nominally identical sinusoidal input currents are generated based on an error signal, which is generated based on comparing a sinusoidal driver signal with feedback from one or more of the K branches. A unit current rotator rotates the K sinusoidal input currents to each of the branches, so that each branch current is formed by a rotating contribution from each of the sinusoidal input currents. Driving each branch with its branch current manifests a respective branch voltage, and differences between the branch voltages can be used to differentially sense pairs of channels.