Fingerprint Sensor Pixel Circuit for High-Voltage Signal Boost
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Solution Overview
Problem
Conventional fingerprint sensors face challenges in charging the top metal with high voltage due to power supply limitations, leading to uncomfortable signal application and reduced signal strength.
Innovation Solution
A unit pixel structure with a sensing electrode, switches, an amplifier, and capacitors that allow for high voltage charging without external signals, enabling increased output signal strength by using driving voltages to charge capacitors and amplify signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high voltage is applied to charge the top metal in conventional fingerprint sensors, then the output signal strength is improved, but the user feels uncomfortable due to external signal application
Solution Approach 1:
The patent introduces a capacitor as an intermediary energy storage element between the power supply and the sensing electrode. The capacitor stores electrical energy and releases it to charge the top metal, mediating the interaction between the power supply system and the sensing element. This allows high voltage charging without direct external signal application to the user's finger, resolving the contradiction between signal strength and user comfort.
2Strength
If high voltage is used to charge the top metal, then the output signal strength is improved, but it is difficult to achieve due to power supply voltage limits within the pixel
Solution Approach 1:
The patent applies preliminary action by charging the capacitor with driving voltages before the actual sensing operation. The capacitor is pre-charged to a high voltage level during a preparation phase, so that when the sensing electrode needs to be charged, the energy is already stored and ready to be released. This preliminary energy storage bypasses the power supply voltage limits during the critical sensing moment.
Solution Approach 2:
The patent employs periodic action through alternating between charging phases and sensing phases. During charging phases, the capacitor is charged with driving voltages; during sensing phases, the stored energy is used to charge the top metal. This periodic alternation allows the system to operate with high voltage effects without requiring the power supply to continuously maintain high voltage, thus overcoming power supply limitations.
3Use of energy by moving object
If the amplifier operates at lower voltage, then power consumption is reduced, but the output signal strength is limited
Solution Approach 1:
The patent segments the voltage function into two distinct parts: the amplifier operates at a low, power-efficient voltage for signal processing, while the capacitor provides high voltage for the specific function of charging the sensing electrode. This segmentation allows each component to operate at its optimal voltage level, with the amplifier consuming minimal power and the capacitor delivering high voltage when needed, thus resolving the contradiction between power consumption and signal strength.
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 enables the fingerprint sensor to output a stronger signal by charging capacitors with high driving voltage, even when the amplifier operates at a lower voltage, enhancing signal strength and comfort during fingerprint scanning.
Implementation Method 1
a sensing electrode located to form a capacitance with an object touching a touch surface
Implementation Method 2
a first capacitor connected between a first input terminal and an output terminal of the amplifier, the first capacitor configured to transmit the signal from the sensing electrode to the output terminal
Implementation Method 3
an amplifier configured to receive a signal from the sensing electrode and amplify the signal
Data Source
AI summary
A unit pixel of a fingerprint sensor is provided. The unit pixel includes a sensing electrode located to form a capacitance with an object touching a touch surface, a first switch connected between a first node and a second node to transmit at least one driving voltage input through the second node, the first node connected to the sensing electrode, the switch configured to the sensing electrode, an amplifier configured to receive a signal from the sensing electrode and amplify the signal, and a first capacitor connected between a first input terminal and an output terminal of the amplifier, the first capacitor configured to transmit the signal from the sensing electrode to the output terminal. The amplifier is configured to output a different output voltage according to the at least one driving based on an operation of the first switch.