Capacitive Fingerprint Sensor Noise Reduction via Differential Driving
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive fingerprint sensors face challenges in accuracy due to factors like chemical impurities and equipment control variations during semiconductor manufacturing, leading to fixed pattern noise in captured images, which increases system cost and complexity.
Innovation Solution
A capacitive image sensor array with capacitive sensing elements that utilize a driving signal with alternate positive and negative waveforms to reduce noise, where the difference in output voltages under these waveforms is used to generate noise-reduced pixel values, mapped to corresponding locations to form a clear fingerprint image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If capacitive fingerprint sensors are manufactured with semiconductor processes to achieve high density, then the sensing element density is improved, but fixed pattern noise increases due to process variations
Solution Approach 1:
The patent applies periodic action by using alternating positive and negative waveforms to drive the capacitive sensing elements. This periodic driving signal enables differential measurement techniques that cancel out fixed pattern noise while maintaining high sensing element density achieved through semiconductor manufacturing processes
Solution Approach 2:
The patent changes the driving signal parameters by applying different voltage levels (positive and negative waveforms) to the capacitive sensing elements. This parameter variation allows the system to measure capacitance changes differentially, thereby reducing fixed pattern noise caused by manufacturing variations
2Object-generated harmful factors
If calibration data is stored to eliminate fixed pattern noise, then the noise reduction is improved, but memory storage space and system cost increase
Solution Approach 1:
The patent implements self-service by enabling the capacitive sensing system to reduce its own fixed pattern noise through differential measurement techniques. The system uses alternating waveform driving and capacitance comparison methods that inherently cancel out noise patterns without requiring external calibration data storage
Solution Approach 2:
The patent converts the harmful fixed pattern noise into a measurable signal by using alternating positive and negative waveforms. The noise pattern becomes part of the differential measurement process, where it is automatically cancelled out, transforming a previously harmful factor into a manageable aspect of the measurement technique
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 accuracy of fingerprint capture by reducing noise, improving image quality, and potentially lowering system costs by minimizing the need for extensive calibration and memory storage for noise reduction.
Implementation Method 1
capacitive fingerprint sensor is based on the principle that the capacitance of a two parallel conductive plates is inversely proportional to the distance between them
Implementation Method 2
The driving signal is a signal with voltage transition or transitions, formed by alternate positive waveform and negative waveform
Data Source
AI summary
A capacitive image sensor and a method for running the capacitive image sensor are disclosed. The capacitive image sensor includes a number of capacitive sensing elements, forming an array, each capacitive sensing element for transforming a distance between a portion of a surface of an approaching finger and a top surface thereof into an output voltage, wherein a value of the output voltage is changed by a driving signal exerted on the finger; an A/D converter, for converting the output voltage into a number and outputting the number; and a signal source, for providing the driving signal to the finger.