Fingerprint Readout Circuit with Voltage Amplification for Signal Contrast
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Solution Overview
Problem
Current fingerprint recognition technologies face challenges in accurately reading out fingerprint signals due to small signal contrast between valleys and ridges, leading to lower readout accuracy and precision.
Innovation Solution
A fingerprint readout circuit comprising a voltage amplifier unit, a fingerprint readout unit, and a source follower unit, where the voltage amplifier unit is coupled to the fingerprint readout unit and the source follower unit, providing both current and voltage amplification to enhance signal amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a three-transistor (3T) structure is used for fingerprint readout, then the circuit can provide current amplification and driving strength, but the voltage difference between fingerprint valleys and ridges remains small and difficult to read out accurately
Solution Approach 1:
The fingerprint readout circuit is segmented into three functional units: a voltage amplifier unit (with first and second transistors) for voltage amplification, a fingerprint readout unit (with third transistor) for signal reading, and a source follower unit (with fourth and fifth transistors) for current amplification. This segmentation allows each unit to perform its specific function optimally, resolving the contradiction by separating voltage amplification from current driving functions.
Solution Approach 2:
The patent combines voltage amplification and current amplification functions into a single integrated circuit structure. The voltage amplifier unit amplifies the voltage difference between fingerprint valleys and ridges, while the source follower unit provides current amplification and driving strength. This merging of functions allows the circuit to simultaneously achieve both voltage signal enhancement and current driving capability.
2Device complexity
If photodiodes are used to detect light reflection from fingerprint ridges and valleys, then the structure is simple, but the electrical signals have smaller differences and are interfered by noise after RC loadings
Solution Approach 1:
The voltage amplifier unit acts as an intermediary between the photodiodes and the fingerprint readout unit. It receives the weak electrical signals from the photodiodes, amplifies the voltage differences, and then passes the enhanced signals to the subsequent stages. This intermediary function prevents signal degradation from RC loadings and noise interference, maintaining measurement precision while keeping the overall structure relatively simple.
3Measurement precision
If signal amplification is increased to improve fingerprint readout accuracy, then the voltage difference between valleys and ridges can be enhanced, but the circuit complexity increases
Solution Approach 1:
Each transistor in the circuit performs multiple functions. For example, the first transistor serves both as part of the voltage amplifier and as a switch controlled by the second voltage signal. The third transistor functions as both a readout device and a current amplifier. This multi-functionality reduces the total number of components needed, achieving signal amplification without proportionally increasing circuit complexity.
Data Source
AI summary
A fingerprint readout circuit and a display panel are disclosed. The fingerprint readout circuit includes a voltage amplifier unit, a fingerprint readout unit, and a source follower unit. The voltage amplifier unit is coupled to the fingerprint readout unit and the source follower unit, and the fingerprint readout unit is coupled to the source follower unit. The fingerprint readout circuit has both current and voltage amplification functions. Therefore, a voltage difference is amplified, facilitating reading out fingerprint signals accurately and enhancing fingerprint readout precision and accuracy.