Fingerprint Sensing Signal Downconversion for Higher SNR
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing fingerprint identification technologies face challenges in amplifying high-frequency fingerprint sensing signals due to low capacitance impedance in feedback loops, resulting in a low signal-to-noise ratio (SNR).
Innovation Solution
The method involves frequency mixing of high-frequency fingerprint sensing signals with a first high-frequency signal to obtain a low-frequency signal, which is then amplified using a capacitive feedback amplifier, leveraging the inverse proportionality of capacitance impedance to signal frequency to achieve significant gain and improve SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency mixing is performed on high frequency fingerprint sensing signals, then the signal-to-noise ratio is improved, but the device complexity increases
Solution Approach 1:
The patent introduces a frequency mixer as an intermediary device that converts high frequency fingerprint sensing signals to low frequency signals. This mediator enables subsequent amplification by the capacitive feedback amplifier, which would be ineffective at high frequencies due to low capacitance impedance. The frequency mixer acts as the crucial intermediary that bridges the gap between high frequency signal acquisition and low frequency amplification.
Solution Approach 2:
The patent changes the frequency parameter of the fingerprint sensing signal from high frequency to low frequency through frequency mixing. This parameter transformation allows the signal to be processed by the capacitive feedback amplifier effectively, as the amplifier's capacitance impedance becomes sufficiently high at low frequencies to provide meaningful amplification gain.
2Measurement precision
If capacitance C in the feedback loop is increased to improve amplification, then the signal amplification improves, but the circuit area increases
Solution Approach 1:
Instead of increasing capacitance C to improve amplification, the patent changes the frequency parameter from high to low. Since capacitance impedance is inversely proportional to frequency (Zc = 1/(2πfC)), lowering the frequency naturally increases the impedance without requiring larger capacitance values, thus avoiding increased circuit area while still achieving effective amplification.
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
This approach increases the signal-to-noise ratio by dozens of times, overcoming the limitations of previous designs and enhancing the fidelity of fingerprint sensing signals.
Implementation Method 1
a frequency mixing step by performing frequency mixing of a collected high frequency fingerprint sensing signal with a first high frequency signal to obtain a low frequency signal
Implementation Method 2
the capacitive sensing element is located between the finger and a sensing chip, and the finger can be capacitively coupled to each capacitive sensing element of the sensor, so that the sensor can sense the capacitance between each capacitive sensing element and a fingerprint muscle
Data Source
AI summary
The present invention relates to the field of fingerprint identification technologies, and provides a method and a system for processing fingerprint sensing signals, and a fingerprint identification terminal. The method includes a frequency mixing step by mixing a collected high frequency fingerprint sensing signal with a first high frequency signal to obtain a low frequency signal; and an amplification step by amplifying the low frequency signal. By using the character that capacitance impedance is inversely proportional to signal frequency, the present invention shifts a fingerprint sensing signal with a high frequency into a signal with a low frequency through frequency spectrum shifting and performs signal amplification on the signal with a low frequency, which can overcome the difficulty in amplifying the high frequency fingerprint sensing signal and thus improves the signal-to-noise ratio SNR.