Diode-Based Fingerprint Sensor Pixel Design
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Solution Overview
Problem
Existing fingerprint sensing technologies face challenges such as high power consumption, inaccuracies due to resistive losses, and complexity in processing algorithms, particularly in compact and flexible sensor designs for applications like contact-less smartcards, where they need to be robust, insensitive to contaminants, and efficient in power usage.
Innovation Solution
A sensor apparatus with diode-based pixel elements that function as both heaters and temperature sensors, allowing individual pixel addressing and thermal signal detection, reducing power consumption and eliminating resistive line losses by using current sources and a flexible substrate, while minimizing production costs through modular design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If temperature sensor arrays are used to detect fingerprint patterns through thermal contact differences, then fingerprint measurement capability is achieved, but power consumption increases and thermal equilibrium is reached quickly requiring complex processing algorithms
Solution Approach 1:
The patent combines the heater and temperature sensor functions into a single integrated pixel element. The same structure that generates heat also detects temperature changes, eliminating the need for separate heater and sensor components. This integration reduces power consumption while maintaining fingerprint detection capability through the thermal contact difference between ridges and valleys.
2Measurement precision
If separate resistors are used as heater and temperature sensing elements in pixel elements, then temperature measurement capability is achieved, but resistive losses in column lines cause inaccuracies and increase power consumption
Solution Approach 1:
The patent extracts the temperature sensing function from separate column line resistors and integrates it directly into the pixel element structure. By using the same pixel structure for both heating and sensing, the system eliminates resistive losses in column lines that would otherwise interfere with temperature measurements and increase power consumption.
3Productivity
If all pixels on a column are heated at the same time to improve measurement speed, then data acquisition rate increases, but power consumption increases significantly
Solution Approach 1:
The patent implements periodic heating where pixels are heated in sequential groups or individually rather than all simultaneously. This allows the system to maintain data acquisition capability while significantly reducing peak power consumption by spreading the heating load over time periods.
4Reliability
If a robust sensor surface is used to withstand wear and contamination, then device lifetime and reliability improve, but sensitivity to fingerprint patterns may be reduced
Solution Approach 1:
The patent employs a flexible membrane structure that provides mechanical robustness and wear resistance while maintaining thermal sensitivity. The thin film nature of the membrane allows it to conform to fingerprint patterns and detect thermal contact differences, achieving both durability and measurement 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
The solution enables a compact, flexible, and low-power fingerprint sensor with reduced power consumption, improved accuracy, and simplified production, suitable for wireless applications like contact-less smartcards, while maintaining robustness and efficiency in data acquisition.
Implementation Method 1
The at least one diode is adapted to be activated by being heated with an applied electric current
Implementation Method 2
the equilibrium temperature of each sensor is a function of the thermal contact between the finger and the sensor. A good thermal contact, corresponding to fingerprint ridges, will typically induce a larger sensor temperature change than a bad thermal contact
Data Source
AI summary
Apparatus for measuring a pattern in a surface of an object, comprising a plurality of pixel or sensor elements being responsive to a physical parameter of the object surface, and means for establishing an overall, segmented picture related to said pattern, and also comprising at least one diode functionally associated with each sensor element for contributing to one or more of the following functions: selectively addressing said sensor element; activating said sensor element; and sensing of said physical parameter.