Fingerprint Sensor Parasitic Capacitance Mitigation
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Solution Overview
Problem
Fingerprint sensors face reduced sensitivity due to parasitic capacitance, which affects their reliability and output dynamic range.
Innovation Solution
A fingerprint sensor design that includes a sensor plate, a voltage source, and a control circuit, along with conductive plates, maintains a predetermined voltage difference during charge and discharge periods to alleviate the impact of parasitic capacitance, using a control circuit to charge and discharge capacitors while keeping the voltage difference consistent between the sensor plate and conductive plates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sensor plate is used to detect capacitance in fingerprint authentication, then the authentication function is achieved, but parasitic capacitance reduces sensitivity and output dynamic range
Solution Approach 1:
The sensor plate is divided into a sensing region and a non-sensing region. The non-sensing region is specifically designed to reduce parasitic capacitance while the sensing region maintains high sensitivity for fingerprint detection. This segmentation allows different regions to serve different functions, resolving the contradiction between authentication reliability and sensitivity.
Solution Approach 2:
Different regions of the sensor plate are assigned different properties: the sensing region has optimized capacitance characteristics for high sensitivity, while the non-sensing region is configured to minimize parasitic capacitance. This local differentiation enables the sensor to achieve both reliable authentication and high sensitivity simultaneously.
2Area of stationary object
If the sensor plate area is increased to improve detection coverage, then more fingerprint area is captured, but parasitic capacitance increases reducing sensitivity
Solution Approach 1:
The sensor plate area is segmented into sensing and non-sensing regions. The non-sensing region extends the physical area for structural purposes without contributing to parasitic capacitance that would degrade sensitivity. This allows the sensor to maintain large area for coverage while preserving sensitivity through functional segmentation.
Solution Approach 2:
A non-sensing region acts as an intermediary between the sensing regions, providing physical extension and structural support while electrically isolating or minimizing its capacitive contribution. This intermediary region allows area expansion without proportionally increasing harmful parasitic capacitance.
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 enhances the sensor's sensitivity by isolating it from parasitic capacitance effects, ensuring consistent performance and reliability.
Implementation Method 1
The sensor plate detects a first capacitance in response to a touch event on the fingerprint sensor
Implementation Method 2
The voltage source establishes a predetermined voltage difference between a first node and a second node
Data Source
AI summary
A fingerprint sensor is disclosed. The fingerprint sensor includes a sensor plate, a voltage source, a control circuit and a first conductive plate. The sensor plate detects a first capacitance in response to a touch event on the fingerprint sensor. The voltage source establishes a predetermined voltage difference between a first node and a second node. The control circuit, connected to the sensor plate via the first node, charges a first capacitor associated with the first capacitance during a charge period, and discharges the first capacitor during a discharge period. The first conductive plate, separated from the sensor plate, is coupled with the voltage source via the second node. During the charge period and the discharge period of the control circuit, a voltage difference between the sensor plate and the first conductive plate is maintained at the predetermined voltage difference.