Fingerprint Sensing Circuit Time-Division Multiplexing
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Solution Overview
Problem
Existing display devices with integrated fingerprint sensing circuits face interference from other signals in the display panel, which can disrupt the voltage on wires and affect fingerprint identification accuracy.
Innovation Solution
The implementation of a display device with a fingerprint sensing circuit that includes a photo detector, a capacitor, a current mirror, and a switch circuit, where the current mirror is turned on during a sensing period to generate a current on a sensing line, allowing the detecting circuit to generate a fingerprint signal without interference from other display signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an optical fingerprint sensing circuit is connected to a detecting circuit through wires in the display area, then the fingerprint sensing function is integrated into the display panel, but the voltage on the wires is disturbed by other signals in the display panel affecting identification accuracy
Solution Approach 1:
The patent employs periodic action by dividing the operation into distinct exposure period and sensing period. During the sensing period, the current mirror is turned on to read out the fingerprint signal, while during the exposure period, the current mirror is turned off to allow the photodetector to accumulate charge without interference. This time-division multiplexing separates the fingerprint sensing operation from other display signals, eliminating voltage disturbances on the sensing lines while maintaining integration in the display panel.
Solution Approach 2:
The patent segments the sensing circuit into independent functional blocks: photodetector, capacitor, current mirror, and switch circuit. Each component is independently controlled and optimized. The current mirror and switch circuit are specifically designed to isolate the fingerprint sensing signal from other display signals, allowing the sensing operation to be separated in time and space from other panel operations, thus reducing interference while maintaining integration.
2Measurement precision
If a current mirror is used to generate current on the sensing line during sensing period, then fingerprint signal accuracy is improved, but the circuit complexity increases
Solution Approach 1:
The current mirror circuit performs multiple functions: it acts as a buffer to transfer the photodetector signal to the sensing line, provides impedance matching, and enables time-division multiplexing by being controlled by the switch circuit. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in circuit complexity while still achieving high measurement precision through controlled current transfer during the sensing period.
Solution Approach 2:
The current mirror serves as an intermediary between the photodetector and the sensing line. It mediates the signal transfer by converting the photodetector's current output into a stable current signal on the sensing line that is resistant to interference from other display signals. This intermediary function isolates the sensitive photodetector from direct connection to the sensing line, reducing the impact of signal disturbances while maintaining a relatively simple overall circuit structure.
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 solution effectively generates a fingerprint signal that is not easily affected by other signals in the display panel, enhancing the accuracy and reliability of fingerprint identification.
Implementation Method 1
Each fingerprint sensing circuit includes a photo detector... the photo detector has a first terminal and a second terminal... the current mirror is turned on to generate a current on the sensing line
Data Source
AI summary
The fingerprint sensing circuit includes a photo detector, a capacitor, a current mirror and a switch circuit. The capacitor has a first terminal electrically connected to the first terminal of the photo detector. The current mirror has an input terminal electrically connected to the first terminal of the photo detector and an output terminal electrically connected to a sensing line. In an exposure period, the switch circuit turns off the current mirror. In a sensing period, the switch circuit turns on the current mirror to generate a current on the sensing line, and the detecting circuit is configured to generate a fingerprint signal according to the current.