Biometric Sensor Scan-Line Reset Circuit for Uniform Detection Values
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Solution Overview
Problem
Optical detection devices with photoelectric conversion elements, such as PIN photodiodes, face differences in detection values due to variations in time constants caused by differences in wiring length of scan lines, leading to inconsistent performance in biometric sensors like fingerprint and vein sensors.
Innovation Solution
A detection device with a matrix configuration of detection elements, featuring reset control scan lines driven by a circuit with transistors that apply specific potentials to reduce the time constant differences, including a first transistor for a high potential, a second transistor in series for a lower potential, and a third transistor in parallel to moderate the potential supply, ensuring consistent signal output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If scan lines with different wiring lengths are used to drive detection elements in a matrix configuration, then the detection area can be covered, but detection values differ due to differences in time constant
Solution Approach 1:
The patent applies different transistor configurations to different regions of the scan line drive circuit. Specifically, transistors with different channel widths (W1 and W2) are used in different segments of the scan line drive circuit to compensate for the varying wiring lengths and capacitances across the detection area, ensuring uniform time constants despite spatial variations.
Solution Approach 2:
The patent changes the electrical parameters (transistor channel widths W1 and W2) of the drive circuit to compensate for the physical parameter variations (wiring length and capacitance) in the scan lines. By adjusting these transistor parameters, the time constant is standardized across all detection elements regardless of their position in the detection area.
2Length of stationary object
If wiring length of scan lines varies across the detection area, then complete coverage is achieved, but time constant differences cause detection value variations
Solution Approach 1:
The patent implements local quality by using transistors with specifically designed channel widths (W1 and W2) in different regions of the scan line drive circuit. This local customization of transistor parameters compensates for the regional differences in wiring length and capacitance, maintaining uniform time constants across the entire detection area.
Solution Approach 2:
The patent achieves equipotentiality in terms of electrical time constant by carefully selecting transistor parameters (channel widths W1 and W2) to balance the varying RC time constants caused by different wiring lengths. This creates an effective equipotential condition where all detection elements experience the same time constant despite physical distance variations.
3Device complexity
If a common scan line drives multiple detection elements, then device complexity is reduced, but detection values differ due to wiring length variations
Solution Approach 1:
The patent modifies the parameters of existing transistors in the common scan line drive circuit (specifically the channel widths W1 and W2) to compensate for wiring length variations. This parameter adjustment approach maintains the simple common scan line architecture while achieving uniform detection values across all elements.
Solution Approach 2:
The patent uses multiple transistors with identical structures and parameters (W1 and W2) replicated across different scan line drive circuits. This copying of transistor configurations ensures consistent time constant compensation throughout the entire detection area while maintaining device simplicity.
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
This configuration reduces variations in detection values across the detection area, enhancing the consistency and accuracy of biometric data capture by mitigating the effects of wiring resistance and parasitic capacitance on the scan lines.
Implementation Method 1
a plurality of photoelectric conversion elements such as positive-intrinsic-negative (PIN) photodiodes are arranged on a substrate
Data Source
AI summary
A detection device includes a plurality of detection elements arranged in a matrix having a row-column configuration in a detection area, a plurality of scan lines each coupled to the detection elements arranged in a first direction, a drive circuit configured to drive the scan lines, a plurality of output signal lines each coupled to the detection elements arranged in a second direction different from the first direction, and a detection circuit configured to be supplied with detection signals from the detection elements through the output signal lines.