Capacitive Skin Contact Sensor Readout for High-Resolution Sensing
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Solution Overview
Problem
Current biometric skin contact sensors face challenges in achieving high resolution and large area coverage due to limitations in capacitive touch sensing technologies, such as sensitivity to environmental noise and parasitic capacitance, which restricts the number of pixels and resolution in capacitive touch sensors.
Innovation Solution
A capacitive biometric skin contact sensor design featuring an array of sensor pixels with thin film transistors and capacitive sensing electrodes, utilizing a current multiplexer and current mirror assembly to dynamically control read-out currents and gain, allowing for flexible operation parameters like resolution, sensitivity, and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pixels in capacitive touch sensors is increased to achieve higher resolution, then measurement precision improves, but parasitic capacitance increases additively limiting the number of pixels that can be combined
Solution Approach 1:
The sensor array is divided into multiple blocks, with each block having its own dedicated readout circuitry. This segmentation prevents parasitic capacitance from adding up across the entire array, as each block operates independently with its own capacitance budget. The patent describes dividing the sensor array into blocks and providing separate readout circuits for each block, thereby overcoming the limiting effect of cumulative parasitic capacitance.
Solution Approach 2:
The patent introduces a block dimension to the sensor architecture, organizing pixels into multiple blocks rather than a single large array. This dimensional reorganization allows scaling to higher resolutions by adding more blocks rather than simply increasing the size of a single array, thus managing parasitic capacitance through spatial distribution.
2Ease of manufacture
If passive matrix capacitive touch sensing is used to reduce device complexity, then ease of manufacture improves, but sensitivity to environmental noise increases
Solution Approach 1:
Active matrix readout circuits serve as intermediary components between the capacitive sensing elements and the external environment. These circuits include amplifiers and signal processing stages that actively compensate for and reject environmental noise, while the modular block structure keeps the complexity manageable through localized processing.
3Reliability
If active matrix capacitive touch sensors are used to reduce environmental noise sensitivity, then reliability improves, but device complexity increases due to switching elements in each pixel
Solution Approach 1:
By dividing the sensor into blocks with shared readout circuitry, the patent reduces the number of independent complex circuits needed. Each block contains a manageable number of pixels with their own readout circuit, rather than requiring fully independent circuits for every pixel across the entire array, thus reducing overall device complexity while maintaining active matrix benefits.
4Measurement precision
If the number of readout channels is increased to support more pixels, then measurement precision improves, but device complexity increases due to more readout circuits
Solution Approach 1:
The patent divides the large sensor array into multiple smaller blocks, each with its own readout circuit. This segmentation allows the system to support a large total number of pixels without requiring a single complex readout system, as each block's readout circuit only needs to handle a manageable subset of pixels, thereby reducing individual circuit complexity while maintaining overall precision.
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
Enables increased flexibility in controlling operational parameters, enhancing resolution and sensitivity while reducing environmental noise interference, thus overcoming limitations in existing capacitive touch sensors.
Implementation Method 1
capacitive sensing electrode... each read-out current being indicative of a proximity to a respective capacitive sensing electrode of a conductive object to be sensed
Data Source
AI summary
A capacitive biometric skin contact sensor configured to resolve the contours of skin in contact with the sensor, wherein the sensor comprises: an array of sensor pixels, wherein each sensor pixel comprises a thin film transistor and a capacitive sensing electrode connected to the thin film transistor; a plurality of gate drive channels, wherein each gate drive channel is arranged to provide a gate drive signal to one or more of the sensor pixels; a plurality of read-out channels, wherein each read-out channel is arranged to receive a read-out current from one or more of the sensor pixels, each read-out current being indicative of a proximity to a respective capacitive sensing electrode of a conductive object to be sensed; a current multiplexer connected to a plurality of the read-out channels to receive read-out currents therefrom; and a current mirror assembly connected to the multiplexer to receive an input current therefrom and to provide a selected gain to the input current; wherein the sensor is configured to control both: (i) the number of read-out currents selected by the multiplexer, and (ii) the selected gain to the input current.