Image Compensation Circuit for Fingerprint Sensor RI Correction
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Solution Overview
Problem
Optical fingerprint sensors face issues due to variations in relative illumination (RI) caused by differences in device characteristics, assembly mismatches, and lens tilt, leading to errors and offsets in image signals.
Innovation Solution
An image compensation circuit and method that includes a gain amplifier, compensation control circuit, memory, and digital-to-analog converter (DAC) to generate and apply compensation values to image signals, addressing RI variations and lens tilt effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical fingerprint sensor module uses a lens and panel structure to capture light, then the fingerprint image can be formed, but relative illumination variations and signal saturation occur due to device characteristics and assembly mismatches
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing compensation values for each pixel in a lookup table before actual fingerprint sensing. The compensation control circuit retrieves these pre-prepared values based on pixel coordinates and applies them to correct relative illumination variations and prevent signal saturation in real-time sensing operations.
Solution Approach 2:
The patent changes the parameter of image signal intensity by applying compensation values that adjust the amplitude of sensing signals. The compensation control circuit modifies signal parameters pixel-by-pixel based on stored compensation data, correcting relative illumination variations and preventing back-end signal saturation while maintaining measurement precision.
2Length of stationary object
If the lens is positioned closer to the sensor to reduce module thickness, then the compactness is improved, but assembly mismatches and lens tilt errors increase causing image signal offsets
Solution Approach 1:
The patent applies local quality by providing unique compensation values for each individual pixel or pixel group based on its specific position in the sensor array. The compensation lookup table stores position-specific correction data that addresses local variations in relative illumination and assembly mismatches, allowing different regions of the sensor to be compensated according to their specific characteristics.
Solution Approach 2:
The patent replaces mechanical precision requirements with an electronic compensation system. Instead of relying on precise mechanical assembly to minimize lens tilt and module spacing errors, the system uses software-based compensation algorithms that calculate and apply correction values to each pixel, substituting mechanical precision requirements with computational correction.
3Measurement precision
If the lens curvature is increased to improve light focusing, then the imaging capability is enhanced, but the contrast of brightness increases causing errors in output image signals
Solution Approach 1:
The patent converts the harmful effect of increased brightness contrast caused by higher lens curvature into a benefit by using it to characterize the relative illumination pattern. The system measures or calculates the specific brightness distribution pattern created by the lens curvature and stores compensation values that counteract this pattern, thereby converting the harmful contrast effect into useful calibration data for correction.
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 effectively compensates for RI differences and lens tilt, improving the uniformity of image signals and enhancing fingerprint recognition by preventing signal saturation and improving image resolution.
Implementation Method 1
The DAC, coupled to the memory and the gain amplifier, is used for converting the plurality of compensation values into a plurality of compensation voltages, respectively, to compensate the plurality of image signals with the plurality of compensation voltages.
Implementation Method 2
The gain amplifier is used for receiving a plurality of image signals from the image sensor and amplifying the plurality of image signals.
Implementation Method 3
The lens 104 collects the light so that the light can reach the pixels in the sensor 106.
Implementation Method 4
The pixels may convert the sensed light intensity into voltage signals, which will be processed by the back-end circuit to output an entire fingerprint image.
Data Source
AI summary
An image compensation circuit for an image sensor includes a gain amplifier, a compensation control circuit, a memory and a digital-to-analog converter (DAC). The gain amplifier is used for receiving a plurality of image signals from the image sensor and amplifying the plurality of image signals. The compensation control circuit is used for generating a plurality of compensation values for the plurality of image signals. The memory, coupled to the compensation control circuit, is used for storing the plurality of compensation values. The DAC, coupled to the memory and the gain amplifier, is used for converting the plurality of compensation values into a plurality of compensation voltages, respectively, to compensate the plurality of image signals with the plurality of compensation voltages.