Capacitive Skin Contact Sensor With Dynamic Readout Control
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Solution Overview
Problem
Existing biometric skin contact sensors face challenges in achieving high resolution and sensitivity while maintaining large area coverage, due to limitations in capacitive touch sensing technologies.
Innovation Solution
A capacitive biometric skin contact sensor is designed with an array of sensor pixels, each comprising a thin film transistor and a capacitive sensing electrode. This sensor includes gate drive channels, read-out channels, a current multiplexer, and a current mirror assembly, allowing for dynamic control of resolution, sensitivity, and other operational parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive touch sensing is used to detect fingerprint contours, then biometric authentication capability is provided, but manufacturing complexity increases due to high resolution requirements (hundreds of pixels per inch)
Solution Approach 1:
The sensor array is divided into multiple pixels arranged in rows and columns, with each pixel independently detecting capacitance changes. This segmentation allows high resolution fingerprint detection through coordinated pixel responses while simplifying individual pixel manufacturing requirements
Solution Approach 2:
The patent varies pixel dimensions and spacing parameters to optimize both resolution and manufacturability. By adjusting these geometric parameters, the system achieves hundreds of pixels per inch resolution while maintaining feasible manufacturing tolerances for each individual pixel element
2Device complexity
If passive matrix capacitive touch sensing is used, then device complexity is reduced, but sensitivity to environmental noise and interference increases
Solution Approach 1:
The system implements feedback mechanisms where pixel responses are continuously monitored and adjusted based on detected noise patterns. This feedback loop enables the sensor to distinguish between environmental interference and actual fingerprint signals, improving reliability while maintaining passive matrix simplicity
Solution Approach 2:
The patent incorporates preliminary noise compensation techniques that preemptively counteract environmental interference. By pre-characterizing noise patterns and applying compensatory algorithms before fingerprint detection, the system reduces noise sensitivity without adding complex active circuitry
3Reliability
If active matrix capacitive touch sensing is used with switching elements in each pixel, then noise resistance improves, but device complexity and parasitic capacitance increase
Solution Approach 1:
The active matrix is segmented into rows and columns with switching elements strategically placed at intersections. This segmentation allows noise resistance through active control while managing complexity by organizing switching elements in a systematic grid pattern rather than requiring complex interconnections
Solution Approach 2:
The patent transitions from planar pixel arrangements to three-dimensional stacked architectures, placing switching elements, sensing electrodes, and readout circuits in different vertical layers. This dimensional change reduces parasitic capacitance by separating conductive elements that would otherwise be close in the planar domain, while maintaining active matrix noise resistance
4Speed
If all pixels of each column are connected in parallel to read-out circuit, then read-out speed is simplified, but parasitic capacitance combines additively limiting sensor size and resolution
Solution Approach 1:
The read-out circuitry is segmented into multiple independent channels, each handling a subset of pixels rather than all pixels in parallel. This segmentation prevents parasitic capacitance from combining additively across the entire array, allowing higher resolution sensors while maintaining efficient read-out speeds through distributed processing
Solution Approach 2:
The patent implements a three-dimensional read-out architecture where pixels are organized in multiple stacks along the vertical dimension. Each stack has its own read-out channel, allowing parallel read-out across stacks while limiting the number of pixels per channel. This approach maintains read-out speed by utilizing vertical parallelism rather than horizontal parallelism, preventing parasitic capacitance accumulation
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
The sensor provides increased flexibility in controlling operational parameters, enabling dynamic adjustment of resolution and sensitivity, as well as optimizing total measurement time and energy consumption, thereby addressing the limitations of existing technologies.
Implementation Method 1
each sensor pixel comprises a thin film transistor and a capacitive sensing electrode connected to the thin film transistor... 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
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; and an analog to digital converter comprising a dual slope integrator arranged to receive, as its input, either an output current or a reference voltage, wherein said output current is based on one or more read-out currents; wherein the biometric sensor is configured to: apply the output current as the input to the dual slope integrator for a charging time period to charge a capacitor of the dual slope integrator; apply the reference voltage as the input to the dual slope integrator for a discharging time period, wherein the discharging time period comprises the amount of time it takes for the capacitor to discharge; and determine the proximity to the one or more respective capacitive sensing electrodes of the conductive body based on an indication of the discharging time period.