Display Pixel Sensing Circuit With Mixed TFT Channels for Fingerprint Readout
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Solution Overview
Problem
Existing display devices experience a decrease in fingerprint sensing capability due to off-leakage currents in the reset transistor of light sensing pixels.
Innovation Solution
The display device incorporates light sensing pixels with a sensing driver that includes transistors with different channel layers made of polysilicon and oxide semiconductor materials, and pixel drivers with transistors formed as N-type MOSFETs, minimizing the off-leakage current and optimizing pixel area usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a reset transistor is used in light sensing pixels for fingerprint authentication, then the pixel can be initialized to a known state, but off-leakage current from the reset transistor degrades fingerprint sensing capability
Solution Approach 1:
The patent extracts the harmful reset transistor from the light sensing pixel circuit while preserving the initialization function through alternative means. The sensing driver circuit is designed to initialize the photodiode node without requiring a reset transistor, thereby eliminating the source of off-leakage current that degrades fingerprint sensing accuracy.
Solution Approach 2:
The patent employs a simple capacitor without associated reset transistor for holding the initialization voltage, accepting that it will discharge over time but replacing it through periodic re-initialization during the sensing process, rather than using a complex reset mechanism that would introduce leakage current.
2Reliability
If the pixel area is increased to improve fingerprint sensing, then more light can be collected, but the display device area and complexity increase
Solution Approach 1:
The patent designs the sensing driver circuit to perform multiple functions within the existing pixel structure: it initializes the photodiode, controls the sensing current, reads out the fingerprint signal, and manages the capacitor charging/discharging cycles. This multi-functionality eliminates the need for additional dedicated circuits that would increase pixel area.
Solution Approach 2:
The patent merges the fingerprint sensing function with the existing display pixel structure by sharing common elements such as the TFT substrate, gate lines, and driver circuitry. The light sensing pixel uses the same base structure as display pixels, with only minimal additional components (photodiode, sensing driver) needed to enable fingerprint authentication.
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 enhances fingerprint sensing capability by reducing off-leakage currents and allows for fingerprint authentication across the entire display area without increasing pixel size, while sharing scan lines and power supply lines with the pixel driver.
Implementation Method 1
a light sensing part including an optical element and a sensing driver, the sensing driver applying a sensing current to a sensing line according to a photocurrent of the optical element
Data Source
AI summary
A display device includes display pixels each including a light emitting part including a light emitting element and a pixel driver applying a driving current to the light emitting element, and light sensing pixels each including a light sensing part including an optical element and a sensing driver, the sensing driver applying a sensing current to a sensing line according to a photocurrent of the optical element. The sensing driver includes a first sensing transistor controlling the sensing current flowing through the sensing line according to a voltage of a first electrode of the optical element, and a second sensing transistor initializing the first electrode of the optical element to a first level voltage. A channel layer of the first sensing transistor and a channel layer of the second sensing transistor are made of different materials.