Fingerprint Sensing Sub-Circuit Separating Transmission and Reception
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Solution Overview
Problem
Ultrasonic fingerprint sensors face issues with residual vibration of the piezoelectric material layer after energization, leading to a poor signal-to-noise ratio due to introduced noise, affecting detection results.
Innovation Solution
The fingerprint sensing sub-circuit includes an acoustic wave generation circuit and an acoustic wave reception circuit, with separate operating modes for transmission and reception, using transistors to control the electro-acoustic and acoustic-electrical conversions, and converting voltage signals into current signals to improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the piezoelectric material layer is energized to generate ultrasonic waves, then fingerprint sensing capability is achieved, but residual vibration occurs after energization stops, introducing noise and degrading signal-to-noise ratio
Solution Approach 1:
The patent divides the sensing element into functionally independent segments: a first sensing element for transmitting ultrasonic waves and a second sensing element for receiving reflected waves. This segmentation allows the transmission and reception functions to be separated spatially, preventing the residual vibration noise from the first element from interfering with the signal detection by the second element, thus resolving the contradiction between sensing capability and signal quality
Solution Approach 2:
The patent introduces a time delay mechanism as an intermediary between the transmission and reception operations. By controlling the second sensing element to operate after a predetermined time delay following the transmission signal, the system allows residual vibrations to subside before signal acquisition begins, effectively mediating between the need for strong transmission and the need for clean signal reception
2Measurement precision
If the piezoelectric material layer vibrates continuously to maintain signal strength, then detection sensitivity is improved, but residual vibration noise increases, degrading measurement precision
Solution Approach 1:
The patent employs spatial segmentation by using distinct first and second sensing elements for transmission and reception respectively. This allows the system to maintain strong transmission signals without compromising reception quality, as the receiving element is positioned to avoid the noise generated by the transmitting element's residual vibrations, thereby maintaining both detection sensitivity and measurement precision
Solution Approach 2:
The patent applies preliminary action by pre-configuring the temporal sequence of operations: the transmission signal is sent first, followed by a predetermined time delay during which residual vibrations occur, and only after this delay does the reception phase begin. This preliminary structuring of the operation timeline ensures that signal acquisition occurs only after disruptive vibrations have subsided, preserving measurement precision
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 eliminates coupling noise from residual vibrations, enhancing the signal-to-noise ratio and improving detection accuracy by separating transmission and reception operations and optimizing signal collection timing.
Implementation Method 1
When an alternating current (AC) voltage is applied to the upper electrode and the lower electrode, the piezoelectric material layer is deformed (or the piezoelectric material layer drives a substrate of an upper film layer and a substrate of a lower film layer to vibrate), thereby the ultrasonic wave is generated and transmitted
Implementation Method 2
When the ultrasonic wave reflected by the fingerprint is propagated to the piezoelectric material layer, it is converted into an AC voltage
Data Source
AI summary
The present disclosure provides a fingerprint sensing sub-circuit, a fingerprint sensing circuit, a fingerprint recognition method, a sensor, a touch display panel and a display device. The fingerprint sensing sub-circuit includes an acoustic wave generation circuit and an acoustic wave reception circuit. The acoustic wave generation circuit is configured to generate an ultrasonic wave. The acoustic wave reception circuit is configured to collect a voltage signal, convert the voltage signal into a current signal, and output the current signal to a signal output end. The acoustic wave generation circuit and the acoustic wave reception circuit are separated from each other, so that the fingerprint sensing sub-circuit operates in a mode where a transmitting operation and a receiving operation are separated from each other.