Optical Fingerprint Circuit Threshold Compensation
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Solution Overview
Problem
Optical fingerprint recognition circuits using LTPS thin film transistors suffer from uneven threshold voltage, which affects the accuracy of signal recognition due to the high cost of silicon-based sensors and the limitations of current in-screen fingerprint recognition technologies.
Innovation Solution
An optical fingerprint recognition circuit is designed with a first thin film transistor, a first switching unit, a second switching unit, a reset compensation unit, and a storage capacitor, where the reset compensation unit adjusts the gate voltage of the first thin film transistor to compensate for its threshold voltage, ensuring accurate signal recognition independent of the transistor's threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LTPS thin film transistor is used for optical fingerprint sensor circuit construction, then the cost is reduced, but the threshold voltage becomes uneven affecting recognition accuracy
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the actual fingerprint recognition operation. The circuit pre-charges the storage capacitor to a voltage that compensates for the LTPS transistor's threshold voltage, ensuring that the transistor operates in its linear region during signal reading. This preliminary setup eliminates the impact of threshold voltage variations on recognition accuracy while maintaining the cost advantages of LTPS technology.
Solution Approach 2:
The patent changes the voltage parameter of the storage capacitor to compensate for threshold voltage variations. By adjusting the pre-charge voltage of the storage capacitor based on the specific threshold voltage characteristics of the LTPS transistor, the circuit transforms the harmful threshold voltage variation into a compensatable parameter, thereby maintaining high recognition accuracy with low-cost LTPS transistors.
2Measurement precision
If silicon-based sensor is used for optical fingerprint recognition, then the recognition accuracy is high, but the cost becomes high
Solution Approach 1:
The patent replaces expensive silicon-based sensors with low-cost LTPS thin film transistor-based circuits. By using LTPS technology that can be manufactured on flexible substrates using low-temperature processes, the invention achieves comparable functionality at a fraction of the cost, making in-screen fingerprint recognition economically viable for mass-market devices.
Solution Approach 2:
The patent substitutes the traditional silicon-based sensor system with an LTPS thin film transistor-based optical detection circuit. This substitution leverages the advantages of LTPS technology, including lower manufacturing costs, flexibility, and compatibility with existing display manufacturing processes, while maintaining the essential optical detection functionality through careful circuit design that compensates for LTPS transistor characteristics.
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 circuit ensures accurate fingerprint recognition by generating a current that is independent of the threshold voltage of the first thin film transistor, enhancing the accuracy of the recognition signal and reducing costs associated with silicon-based sensors.
Implementation Method 1
The photodiode D10 receives an optical signal and generates a leakage current, so that a voltage of the gate of the first thin film transistor T10 is changed correspondingly
Data Source
AI summary
An optical fingerprint recognition circuit and a display device are provided, which includes a first thin film transistor, a first switching unit, a second switching unit, a reset compensation unit, a storage capacitor, and a photodiode. The reset compensation unit resets a voltage of the gate of the first thin film transistor under the control of a reset signal, and the voltage is set to a sum of a predetermined voltage and a threshold voltage of the first thin film transistor through a reference voltage under the control of the reset signal, thereby compensating the threshold voltage. After the photodiode receives the light signal and changes the voltage according to the light signal, the first thin film transistor generates a corresponding current according to the voltage of its gate, which is independent of the threshold voltage. The accuracy of a recognition signal is ensured.