Two-Stage Photocurrent Amplification for Fingerprint Sensing
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Solution Overview
Problem
Current fingerprint recognition technologies face challenges in accurately amplifying small photocurrents from photodiodes in mobile devices, leading to device accuracy issues and difficulties in integrating large resistance resistors for amplification within integrated circuit chips.
Innovation Solution
A current amplification circuitry that includes a signal generator, current mirrors, operational amplifiers, and feedback resistors, which perform two stages of amplification to reduce the resistance requirements in the second amplification circuit, facilitating integration and precision, and includes a photodiode coupled between the voltage input terminal and the current mirror for amplifying photocurrents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large resistance resistors are used to amplify photocurrents, then amplification precision is improved, but integration difficulty increases
Solution Approach 1:
The patent divides the amplification process into two separate stages: a first current amplification circuit and a second current amplification circuit. The first stage uses a transimpedance amplifier with a first resistor to convert photocurrent to voltage, while the second stage uses a second transimpedance amplifier with a second resistor to further amplify the signal. This segmentation allows each resistor to have smaller resistance values that can be integrated on-chip, while achieving the overall high amplification precision through cascaded stages.
Solution Approach 2:
The patent transitions from a single-dimension amplification approach (one large resistor) to a two-dimension approach (two smaller resistors in cascade). By adding the temporal dimension of sequential amplification stages, the system achieves equivalent or superior precision without requiring a single large resistance value that would be difficult to integrate.
2Measurement precision
If two stages of amplification are used, then amplification precision is improved, but device complexity increases
Solution Approach 1:
The patent employs operational amplifiers that perform multiple functions: they act as voltage followers to buffer signals, as transimpedance amplifiers to convert current to voltage, and as gain stages to amplify signals. By making these components multi-functional, the circuit achieves high amplification precision through two stages without proportionally increasing overall device complexity, as the same operational amplifier blocks are reused with different configurations.
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 proposed solution effectively amplifies photocurrents with reduced resistance values, improving device precision and enabling the integration of high-precision amplification circuits within mobile devices, thereby enhancing fingerprint recognition accuracy.
Implementation Method 1
a photodiode coupled between the voltage input terminal and the current mirror for amplifying photocurrents
Implementation Method 2
The current mirror can be configured to amplify a current from the voltage input terminal in the case that there is a voltage difference between the voltage signal provided by the signal generator and a voltage signal provided by the voltage input terminal
Implementation Method 3
The operational amplifier is coupled to the voltage input terminal via a second, noninverting, input terminal and configured to amplify the amplified current
Data Source
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AI summary
Embodiments of the present disclosure provide a current amplification circuitry and a driving method thereof, and a fingerprint detection device. The current amplification circuitry includes a voltage control circuit, a plurality of first current amplification circuits, and a second current amplification circuit. The voltage control circuit provides a voltage control signal to the plurality of first current amplification circuits. The first current amplification circuit includes a current mirror, and the current mirror is coupled to a voltage input terminal, the voltage control circuit and a first input terminal of the second current amplification circuit. The first current amplification circuit amplifies a current from the voltage input terminal according to the voltage control signal provided by the voltage control circuit, and provides the amplified current to the second current amplification circuit. The second current amplification circuit is coupled to the voltage input terminal via a second input terminal and amplifies the amplified current.