Optical Fingerprint Sensing Common Mode Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fingerprint sensing systems face challenges in providing improved signal quality due to weak signals and common-mode noise, which can lead to saturation of capacitors and affect measurement performance, especially with temperature variations.
Innovation Solution
A fingerprint sensing system with pixel elements that include a photo-sensitive element, an integrating capacitor, and a current source arrangement to compensate for common-mode signal currents, using voltage-to-current converters and common-mode sensing circuitry to dynamically adjust voltage and compensate for ambient and temperature-related noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical fingerprint sensing is implemented with photo-sensitive elements, then fingerprint sensing capability is provided, but common-mode signal current causes saturation and reduces measurement precision
Solution Approach 1:
The patent extracts and separates the common-mode signal current from the fingerprint signal by introducing dedicated common-mode sensing circuitry that measures only the common-mode component. This allows the common-mode signal to be isolated and compensated independently, preventing saturation of the integrating capacitor while preserving the fingerprint measurement precision.
Solution Approach 2:
The patent implements feedback by using the output from common-mode sensing circuitry to dynamically adjust the current source arrangement. The sensed common-mode signal is fed back to the current source, which automatically compensates for common-mode variations in real-time, thereby maintaining measurement precision without saturation.
2Measurement precision
If integrating capacitor is used to accumulate weak fingerprint signals, then signal detection capability is improved, but saturation occurs more easily due to common-mode current
Solution Approach 1:
The patent introduces a current source arrangement as an intermediary between the photo-sensitive element and the integrating capacitor. This intermediary actively compensates for common-mode current by providing an equal and opposite current, thereby protecting the integrating capacitor from saturation while allowing it to continue accumulating weak fingerprint signals effectively.
Solution Approach 2:
The patent applies preliminary anti-action by using the current source arrangement to preemptively counteract the common-mode current before it can cause saturation of the integrating capacitor. The compensation current is applied in advance and continuously adjusted to prevent saturation, ensuring reliable operation.
3Area of stationary object
If sensing area is increased to cover larger display areas, then fingerprint sensing coverage is improved, but temperature variations and ambient light effects increase
Solution Approach 1:
The patent segments the sensing system into pixel elements with individual photo-sensitive elements, integrating capacitors, and current source arrangements. This segmentation allows each pixel to independently compensate for local temperature and ambient light variations, enabling large sensing area coverage while maintaining performance across the entire area.
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting the current source arrangement based on sensed temperature and ambient light conditions. The common-mode sensing circuitry detects changes in these parameters, and the current source automatically adjusts its compensation current to maintain optimal performance across varying environmental conditions.
4Ease of manufacture
If TFT technology is used for cost-efficient implementation, then manufacturing cost is reduced, but signal quality and temperature stability are compromised
Solution Approach 1:
The patent applies self-service by implementing on-chip common-mode sensing circuitry and current source arrangements that automatically compensate for TFT-specific issues such as temperature drift and signal variability. The system self-corrects for the limitations of TFT technology, maintaining high measurement precision while using cost-efficient manufacturing.
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 signal quality by reducing saturation risks and extending the usable temperature range, leading to improved measurement performance and larger sensing areas with cost-efficient implementation using TFT or CMOS technologies.
Implementation Method 1
a photo-sensitive element configured to provide a current including a fingerprint signal current component and a common-mode signal current component
Data Source
AI summary
A fingerprint sensing system for sensing a finger surface of a finger, comprising: a plurality of pixel elements, each pixel element in the plurality of pixel elements comprising: a photo-sensitive element configured to provide a current including a fingerprint signal current component and a common-mode signal current component; and an integrating capacitor including a first electrode coupled to the photo-sensitive element for receiving the current provided by the photo-sensitive element, and a second electrode; and a current source arrangement coupled to the first electrode of the integrating capacitor of each pixel element in the plurality of pixel elements.