Mutual Capacitance Sensing Circuit for Touch Position Detection
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Solution Overview
Problem
Conventional capacitance sensing technologies face challenges in accurately determining the proximity and position of objects on multi-dimensional sensor arrays, particularly in achieving high signal-to-noise ratios and resolving low sensitivity points, which affects the precision of touch sensing applications.
Innovation Solution
The proposed solution involves a system that drives all electrodes with periodic signals to induce mutual capacitance between two sets of electrodes, allowing for the detection of object positions by measuring changes in mutual capacitance between individual electrodes of one set and multiple electrodes of another set, using selection circuits, demodulator circuits, and current-to-code converters to enhance sensing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If self-capacitance sensing is used to detect object proximity, then the sensing circuit is simple, but the signal-to-noise ratio is low and sensing precision deteriorates
Solution Approach 1:
The electrode array is segmented into multiple independent electrodes that can be individually driven and sensed. Each electrode can function as either a transmit electrode or a receive electrode, allowing the system to measure mutual capacitance between specific electrode pairs. This segmentation enables precise localization and improved signal-to-noise ratio by focusing measurements on specific regions rather than using a single self-capacitance measurement.
Solution Approach 2:
The patent introduces a mutual capacitance measurement mechanism as an intermediary between the electrode and the sensing circuit. Instead of directly measuring self-capacitance, the system measures the mutual capacitance between a transmit electrode and a receive electrode, with the object's presence affecting this mutual capacitance. This intermediary measurement approach significantly improves the signal-to-noise ratio and sensing precision.
2Device complexity
If conventional capacitance sensing is used, then the device structure is simple, but low sensitivity points cannot be resolved
Solution Approach 1:
The patent transitions from one-dimensional self-capacitance measurements to two-dimensional mutual capacitance measurements by introducing both transmit and receive electrode dimensions. The sensor array is configured with electrodes disposed in different orientations (e.g., row electrodes and column electrodes), allowing the system to measure capacitance interactions across two spatial dimensions. This dimensional expansion enables the system to resolve low sensitivity points and provide more comprehensive coverage of the sensing area.
Solution Approach 2:
The system dynamically assigns electrodes to different functional roles (transmit or receive) based on measurement requirements. The controller can switch electrode configurations and selectively activate different electrode pairs for measurement, allowing the system to adapt to different sensing needs and resolve sensitivity variations across different regions of the sensor array.
3Measurement precision
If mutual capacitance sensing between multiple electrodes is implemented, then sensing resolution improves, but device complexity increases
Solution Approach 1:
The patent designs the electrode array and control circuitry to be multi-functional. The same electrode array can perform both transmit and receive functions, and the control circuit can selectively configure electrodes for different measurement modes. This universality allows the system to achieve high-resolution mutual capacitance sensing without proportionally increasing hardware complexity, as existing components serve multiple purposes.
Solution Approach 2:
The system uses the electrode array itself to generate the measurement signals and perform the sensing functions. The transmit electrodes actively drive signals that induce currents in receive electrodes, and the same electrode structure serves as both the stimulus source and the measurement target. This self-service approach reduces the need for additional external components and minimizes overall device complexity while maintaining high sensing resolution.
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 improves the signal-to-noise ratio and enhances sensing resolution, enabling more accurate detection of object positions and proximity, particularly at low sensitivity points, compared to traditional self-capacitance sensing methods.
Implementation Method 1
A mutual capacitance (Cm) may exist between two electrodes: a receive (Rx) electrode 1502-0 and a transmit (Tx) electrode 1502-1. A periodic signal may be transmitted on the Tx electrode 1502-1. Due to mutual capacitance (Cm), the electrical signal at the Tx electrode 1502-1 may induce a current on the Rx electrode 1502-0.
Data Source
AI summary
A capacitance sensing system may include a first selection circuit that couples N electrodes of a first electrode set to a capacitance sense circuit; and a second selection circuit that couples M electrodes of a second electrode set, substantially simultaneously, to a signal generator circuit as a group to induce current in the N electrodes by mutual capacitance between the M and N electrodes; wherein N is at least one, and M>N.