Electric Field Fingerprint Sensor Parasitic Capacitance Compensation
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Solution Overview
Problem
Conventional electric field type fingerprint identification apparatuses have complex structures, high costs, limited design flexibility, mutual interference between units due to parasitic capacitors, and inability to distinguish fingerprints from prosthetic fingers.
Innovation Solution
An electric field type fingerprint identification apparatus with a signal acquisition module and a signal processing module, featuring a signal acquisition unit array with sensing capacitors, and state control units to coordinate charging and discharging processes, reducing parasitic interference and enabling identification of prosthetic fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two transistors serving as controlled switching devices are adopted to achieve basic fingerprint identification function, then the fingerprint identification function is achieved, but the structure of the fingerprint identification basic unit becomes complicated and device cost increases
Solution Approach 1:
The patent extracts and eliminates the parasitic capacitor from the circuit model by introducing a compensation capacitor that is electrically connected in parallel with the sensing capacitor. This compensation capacitor is specifically designed to cancel out the effect of the parasitic capacitor, thereby simplifying the overall circuit structure while maintaining the fingerprint identification function without requiring additional complex switching devices
Solution Approach 2:
The patent discards the harmful effect of the parasitic capacitor by using a compensation capacitor to recover or neutralize its influence. The compensation capacitor is configured to have an equal but opposite capacitive effect that cancels the parasitic capacitor's interference, effectively removing the harmful factor while preserving the useful sensing function
2Device complexity
If a single form of circuit is used, then the circuit design is simplified, but diverse design solutions can not be obtained based on application requirement
Solution Approach 1:
The patent introduces a state control unit that can dynamically control the electrical connection states of multiple capacitors (sensing capacitor, compensation capacitor, and reference capacitor) in different operational modes. This allows the same basic circuit structure to adapt to different application requirements by reconfiguring which capacitors are active, providing diverse design solutions while maintaining a relatively simple base circuit form
Solution Approach 2:
The patent employs dynamic control through the state control unit that can change the electrical connection states of various capacitors based on different measurement phases (charging phase, discharging phase, compensation phase). This dynamic reconfiguration enables the circuit to serve multiple functions and adapt to different application scenarios without requiring multiple fixed circuit designs
3Productivity
If multiple fingerprint identification basic units are arranged closely, then the device integration is improved, but mutual interference exist between electric fields of basic units due to parasitic capacitors
Solution Approach 1:
The patent converts the harmful parasitic capacitor effect into a beneficial compensation by introducing a specifically designed compensation capacitor. The compensation capacitor is configured to generate an equal and opposite capacitive effect that actively cancels the parasitic interference, allowing closely integrated basic units to operate without mutual interference while maintaining high device integration
4Measurement precision
If the change quantity of electric charge is measured to determine fingerprint features, then fingerprint identification is achieved, but the change quantity may be changed by parasitic capacitors making accurate measurement difficult
Solution Approach 1:
The patent introduces a compensation capacitor as an intermediary element that mediates between the parasitic capacitor and the measurement process. This compensation capacitor acts as a buffer that actively counteracts the parasitic capacitor's influence on the electric charge measurement, thereby protecting the accuracy of the fingerprint feature measurement from parasitic interference
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 simplifies the structure, reduces costs, adapts to multiple application requirements, eliminates mutual interference, and effectively identifies fingerprints from both real and prosthetic fingers, enhancing security and reliability.
Implementation Method 1
Each of the signal acquisition units includes a sensing capacitor. The signal processing module includes a measuring state signal processing unit and a to-be-measured state signal processing unit, the measuring state signal processing unit is configured to acquire capacitance change quantities respectively caused by convex and concave textures of fingerprints from the signal acquisition unit by charging and discharging the sensing capacitor
Implementation Method 2
Charging and discharging quantities of a parasitic capacitor between the signal acquisition unit in the measuring state and the signal acquisition unit in the to-be-measured state are restrained by controlling the measuring state signal processing unit and the to-be-measured state signal processing unit to coordinate charging and discharging processes of the sensing capacitors
Data Source
AI summary
Provided are an electric field type fingerprint identification apparatus and a state control method and a prosthesis identification method. The electric field type fingerprint identification apparatus includes a signal acquisition module and a signal processing module. In a case that a measuring state signal processing unit is electrically connected to a signal acquisition unit, a to-be-measured state signal processing unit is at least electrically connected to at least one signal acquisition unit peripheral to the signal acquisition unit in a measuring state. Charging and discharging processes of sensing capacitors electrically connected to the measuring state signal processing unit and the to-be-measured state signal processing unit are coordinated to restrain charging and discharging quantities of a parasitic capacitor between the signal acquisition unit in the measuring state and the signal acquisition unit in a to-be-measured state.