Fingerprint Detection Circuit With Switch-Based DC Biasing
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Solution Overview
Problem
Capacitive fingerprint identification systems require complex biasing circuits to maintain accuracy, which complicates the circuit structure and increases the risk of security breaches due to password vulnerabilities in portable devices.
Innovation Solution
A fingerprint detecting circuit with a single-input, single-output inverting amplifier and a switch that establishes a direct current (DC) operating point, eliminating the need for additional biasing circuits and enhancing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If complex biasing circuits are used to maintain the DC operating point, then the accuracy of fingerprint detection is improved, but the circuit structure becomes complicated
Solution Approach 1:
The patent extracts the DC biasing function from the traditional complex biasing circuit and implements it through a simple switch connected between the input and output terminals of the inverting amplifier. This switch-based approach isolates the biasing function from the rest of the circuit, achieving accurate DC operating point establishment without requiring complex additional circuitry.
Solution Approach 2:
The inverting amplifier is designed to serve multiple functions: it acts as both the signal amplification stage and the DC biasing mechanism. By connecting a switch between its input and output terminals, the same amplifier structure provides both amplification and biasing functions, eliminating the need for separate dedicated biasing circuits.
2Device complexity
If simple biasing circuits are used, then the circuit structure is simplified, but the accuracy of fingerprint detection deteriorates
Solution Approach 1:
The inverting amplifier serves itself by establishing its own DC operating point through the switch connection between its input and output terminals. This self-biasing mechanism eliminates the need for external complex biasing circuits while maintaining accurate operation, as the amplifier uses its own output to regulate its input biasing condition.
3Ease of operation
If password protection is used, then user identification is achieved, but security risks increase due to password spreading or cracking
Solution Approach 1:
The patent replaces the software-based password protection mechanism with a biometric fingerprint recognition system. This substitution transitions from a logical/security-vulnerable system to a physical/biological authentication method, enhancing security while maintaining user convenience through the unique physiological characteristics of fingerprints.
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 provides a simple circuit structure with high accuracy for fingerprint detection, reducing the risk of security breaches and eliminating the need for complex biasing circuits, thereby enhancing data security in portable devices.
Implementation Method 1
the capacitive fingerprint identification system utilizes a metal electrode to receive a touch from a user, and the fingerprint detecting circuit therein may transform a capacitance between the metal electrode and the finger into a voltage signal
Implementation Method 2
a switch, configured for establishing a direct current (DC) operating point of the inverting amplifier
Data Source
AI summary
The present invention, belonging to a field of fingerprint detecting technology, relates to a fingerprint detecting circuit including: a first conductive layer; a second conductive layer; an inverting amplifier, comprising a single input terminal coupled to the first conductive layer; and an output terminal coupled to the second conductive layer; and a switch, configured for establishing a DC operating point of the inverting amplifier, wherein a terminal of the switch is coupled to the input terminal, and another terminal of the switch is coupled to the output terminal. The present invention utilizes the inverting amplifier with single input single output and the switch to quickly and correctly establish the DC biasing point of the inverting amplifier, and convert the sensing capacitance into the output signal. No need for another biasing circuit. The circuit structure thereof is simple and the accuracy is high.