Quasi-Differential Receive Demodulator for Faster Capacitive Sensing
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Solution Overview
Problem
Large touch sensor matrices face inefficiencies in measurement speed due to the increased number of self capacitance sensors, which limits the ability to detect conductive objects effectively, especially when not all sensors support parallel sensing.
Innovation Solution
The implementation of a quasi-differential channel with integration capacitors in a demodulation circuit for mutual capacitance sensors, allowing for the storage and processing of charge changes induced by conductive objects, enhances detection efficiency by compensating for baseline capacitance and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the number of self capacitance sensors is increased to cover larger touch sensor matrices, then the sensing coverage area is improved, but the measurement time increases
Solution Approach 1:
The patent divides the touch sensor matrix into multiple zones or groups that can be measured in parallel. By segmenting the large matrix into smaller sub-matrices and using multiple measurement channels simultaneously, the system maintains comprehensive sensing coverage while reducing the total measurement time compared to sequential measurement of all sensors.
2Measurement precision
If self capacitance sensors are used to detect conductive objects, then the detection capability is improved, but the baseline capacitance interference increases
Solution Approach 1:
The patent extracts and removes the baseline capacitance component from the measurement signal. By separately measuring and subtracting the baseline capacitance (the capacitance without any conductive object present) from the total measured capacitance, the system isolates the signal caused by conductive objects, thereby improving detection precision while eliminating the harmful baseline interference.
Solution Approach 2:
The patent applies preliminary anti-action by pre-measuring the baseline capacitance before actual touch detection and using this information to compensate for interference during measurement. The system performs baseline characterization in advance and uses this data to cancel out the baseline capacitance effect during operational measurements, improving detection accuracy.
3Productivity
If parallel sensing is implemented to increase measurement speed, then the productivity is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple measurement functions into a unified parallel sensing architecture. By combining multiple sensor groups and measurement channels into a coordinated parallel operation system with shared control and processing resources, the system achieves high-speed measurement while avoiding the complexity that would result from completely independent measurement systems for each channel.
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 faster and more accurate detection of conductive objects by storing charge differentially, reducing the impact of baseline capacitance and improving measurement speed in touch sensor devices.
Implementation Method 1
The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the sensor
Implementation Method 2
The implementation of a quasi-differential channel with integration capacitors in a demodulation circuit for mutual capacitance sensors, allowing for the storage and processing of charge changes induced by conductive objects
Data Source
AI summary
A first integration capacitor stores charge from a positive signal portion. A second integration capacitor stores charge from negative signal portion. The voltage across the first and second integration capacitors is measured differentially. The presence of a conductive object proximate to a capacitance sensing element is detected based on the measured differential voltage between the first and second integration capacitors.