Capacitive Fingerprint Circuit With Adaptive Voltage Gain Control
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Solution Overview
Problem
Capacitive fingerprint detection circuits face challenges in accurately distinguishing between ridge and valley capacitance due to small differences in output voltages, leading to reduced signal-to-noise ratio and affected accuracy, especially since each person's finger characteristics are unique.
Innovation Solution
A fingerprint detection circuit that applies an excitation signal to generate ridge and valley capacitors, with a processing module that amplifies voltages and adjusts the excitation voltage, predetermined factor, and regulation voltage to ensure a difference greater than or equal to a threshold, thereby enhancing the signal-to-noise ratio for improved recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed predetermined factor is used to amplify the output voltage, then the circuit structure remains simple, but the detection accuracy deteriorates due to individual finger differences
Solution Approach 1:
The patent transforms the fixed predetermined factor into a dynamic adjustable parameter. The processing module automatically adjusts the amplification factor based on the detected voltage difference and a predetermined threshold, adapting to individual finger characteristics without requiring complex manual calibration or changing circuit hardware
Solution Approach 2:
The patent changes the amplification factor parameter dynamically based on detected voltage differences. When the voltage difference between ridge and valley capacitance is small, the system increases the amplification factor to enhance the signal difference, thereby improving detection accuracy while maintaining circuit simplicity
2Stability of the object's composition
If the voltage difference between ridge and valley capacitance is small, then the circuit operates stably, but the signal-to-noise ratio deteriorates, making recognition difficult
Solution Approach 1:
The patent implements a feedback mechanism where the processing module continuously monitors the voltage difference between ridge and valley capacitance signals. Based on this feedback and comparison with a predetermined threshold, the system automatically adjusts the amplification factor to optimize the signal-to-noise ratio while maintaining stable circuit operation
Solution Approach 2:
The patent applies preliminary amplification to the voltage signals before further processing. By pre-amplifying the voltage difference between ridge and valley capacitance using an adjustable amplification factor, the system enhances the signal strength early in the processing chain, improving the signal-to-noise ratio for subsequent recognition algorithms
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 adjusted differences between amplified voltages result in a higher signal-to-noise ratio, facilitating better fingerprint detection and recognition, thus improving the accuracy and effectiveness of the fingerprint detection process.
Implementation Method 1
a capacitive fingerprint detection circuit in a chip has advantages of small size and low power consumption... detects fingerprint ridge information and fingerprint valley information... ridge capacitance generated between the fingerprint ridge and the sensing unit and a valley capacitance generated between the fingerprint valley and the sensing unit
Data Source
AI summary
The present disclosure provides a fingerprint detection circuit and method. The circuit includes a fingerprint collecting module and a processing module. The fingerprint collecting module includes a plurality of collecting units, and each collecting unit has a regulation voltage and is configured to output a first voltage or a second voltage according to a capacitance value of one of ridge capacitors, a capacitance value of one of ridge capacitors and the regulation voltage. The processing module is configured to amplify the first and second voltages by a predetermined factor, to calculate a difference between the amplified first and second voltages, and to determine whether the difference is greater than or equal to the predetermined threshold. If no, the processing module adjusts at least one parameter, and configures the fingerprint detection circuit using at least one adjusted parameter.