Fingerprint Detection Circuit With Nonlinear Ridge-Valley Amplification
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Solution Overview
Problem
Capacitive fingerprint detection circuits face challenges in amplifying output voltage differences between ridge and valley capacitances effectively, leading to difficulties in identifying finger characteristics due to limited amplification factors causing overflow or insufficient signal differentiation.
Innovation Solution
A fingerprint detection circuit with a signal amplifier, capacitor, rheostat, and switch unit configuration that creates a non-linear relationship between output voltage and capacitance, allowing for locally linear amplification and improved signal-to-noise ratio by controlling the rheostat's connection in parallel with the capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large amplification factor is used to amplify the output voltage difference between ridge and valley capacitances, then the signal differentiation is improved, but the output voltage exceeds the range causing data overflow
Solution Approach 1:
The patent introduces a dynamic amplification mechanism where the amplification factor is not fixed but varies based on the input signal characteristics. The circuit automatically adjusts the amplification level to maximize signal differentiation while preventing overflow, resolving the contradiction between needing high amplification for precision and avoiding overflow for reliability.
Solution Approach 2:
The patent changes the amplification parameter dynamically based on the detected capacitance values. By monitoring the input signal range and adjusting the amplification factor accordingly, the system achieves optimal signal differentiation without causing data overflow, thus resolving the technical contradiction.
2Reliability
If a small amplification factor is used to avoid data overflow, then the output voltage remains within range, but the difference between ridge and valley voltages becomes too small to identify
Solution Approach 1:
The patent implements a dynamic amplification system that adjusts the amplification factor based on real-time signal conditions. When the input signal difference is small, the amplification factor increases to enhance differentiation; when the signal difference is large, the amplification factor decreases to prevent overflow, thus resolving the contradiction between reliability and measurement precision.
Solution Approach 2:
The patent employs a feedback mechanism where the output signal characteristics are monitored and used to adjust the amplification factor. This closed-loop control ensures that the amplification is optimized for each measurement, achieving both sufficient signal differentiation and prevention of data overflow.
3Device complexity
If a fixed amplification factor is used, then the circuit design is simple, but it cannot simultaneously optimize both ridge and valley detection across different capacitance ranges
Solution Approach 1:
The patent transitions from a fixed amplification factor to a dynamic adjustment mechanism. The circuit automatically adapts the amplification level based on the detected capacitance characteristics, enabling optimized detection accuracy for both ridge and valley across different ranges while maintaining manageable circuit complexity through automated control.
Solution Approach 2:
The patent changes the amplification parameter dynamically based on the input signal characteristics. By automatically adjusting the amplification factor according to the detected capacitance values, the system achieves optimized detection accuracy without requiring complex manual configuration, thus resolving the contradiction between device complexity and measurement precision.
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
Enhances the difference between ridge and valley voltage signals, resulting in a higher signal-to-noise ratio that improves fingerprint detection accuracy and recognition.
Implementation Method 1
there is a difference between a ridge capacitance generated between the fingerprint ridge ridge the sensing unit and a valley capacitance generated between the fingerprint valley and the sensing unit
Data Source
AI summary
A fingerprint detection circuit and an electronic device are provided. The fingerprint detection circuit is configured to apply an excitation signal to a finger so as to generate finger capacitors, and the fingerprint detection circuit includes: a signal amplifier having a negative input terminal connected with one of the finger capacitors, a positive input terminal connected with a ground terminal, and an output terminal to output an output voltage according to a capacitance value of the one of the finger capacitors; a capacitor connected between the negative terminal and the output terminal of the signal amplifier; a rheostat; and a switch unit connected with the rheostat in series and configured to control the rheostat to be connected with the capacitor in parallel, such that the output voltage has a non-linear relationship with the capacitance value of the one of the finger capacitors.