Sensor Pixel Circuit With Coupling Pulse For Fingerprint Detection
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Solution Overview
Problem
The challenge is to enhance the detection performance of sensor pixels, which are weakened by thick protective layers reducing capacitance and susceptibility to electrostatic discharge (ESD), and interference from foreign materials on the sensor surface.
Innovation Solution
A sensor pixel design that includes a detection electrode forming capacitance with a recognition target, a sensor pixel circuit with transistors and capacitors, and a configuration that applies a coupling pulse to adjust the detection signal, while being resilient to ESD through a DC voltage supply, thereby improving detection accuracy and immunity to ESD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick protective layer is used to protect the sensor surface, then the sensor surface is better protected, but capacitance between the recognition target and sensor pixel becomes smaller, making it difficult to detect the recognition target
Solution Approach 1:
A coupling pulse is periodically applied to the recognition target (fingerprint) through the protective layer. This periodic coupling pulse modulates the capacitance signal, enabling detection despite the thick protective layer. The periodic action allows the sensor to overcome the capacitance reduction caused by the protective layer while maintaining detection accuracy.
2Reliability
If ESD protection measures are added to protect against electrostatic discharge, then reliability against ESD is improved, but device complexity increases
Solution Approach 1:
The ESD protection function is extracted as a separate dedicated circuit block connected in parallel to the detection electrode. This ESD protection circuit includes specific transistors and diodes designed solely for ESD protection, isolating the protection function from the main sensing circuitry. This approach provides robust ESD protection while minimizing impact on the complexity of the core sensing circuit.
3Measurement precision
If foreign materials are present on the sensor surface, then detection accuracy is maintained, but false detection occurs when the protective layer is thick
Solution Approach 1:
The sensor system uses feedback mechanisms to distinguish between genuine recognition targets (fingertips) and foreign materials. The coupling pulse technique combined with capacitance measurement provides characteristic signal patterns that enable the system to differentiate between valid targets and contaminants, maintaining detection accuracy even with foreign materials present on the sensor surface.
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 effectively enhances detection performance by compensating for reduced capacitance due to thick protective layers and protects against ESD, ensuring reliable operation even with foreign materials on the sensor surface.
Implementation Method 1
a detection electrode that forms capacitance with a recognition target
Implementation Method 2
a configuration that applies a coupling pulse by contacting the recognition target, wherein the sensor supplies a DC voltage to the plurality of sensor pixels for resetting, and the detection signal may be changed according to the coupling pulse
Data Source
AI summary
A sensor pixel according to a feature of the present invention includes: a detection electrode that forms capacitance with a recognition target; and a sensor pixel circuit that is connected to the detection electrode, generates a detection signal by using the detection electrode, and to which a DC voltage for resetting is supplied, wherein a coupling pulse is periodically applied to the recognition target that forms the capacitance with the detection electrode, and the detection signal may be changed according to the coupling pulse.