Ambient Light Sensor Calibration Using Reference Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current ambient light sensors used in applications like mobile phones and cameras have inconsistent performance due to manufacturing variations, leading to increased costs and limited ability to account for aging and temperature effects, with existing solutions either reducing yield, adding to test costs, or requiring non-volatile memory for calibration.
Innovation Solution
A method involving a light-sensitive pixel that integrates charge over time, converting it to digital form, with calibration using a reference signal and external resistor, allowing for cyclic calibration and adjustment of pixel signals for improved consistency and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measuring output during test and discarding unsatisfactory devices, then measurement precision is improved, but productivity deteriorates due to greatly reduced yield
Solution Approach 1:
The patent applies preliminary action by performing calibration at the time of manufacture to determine individual device characteristics and store correction factors in non-volatile memory. This allows devices to be used as-is without discarding, while still achieving consistent measurements through software compensation, thus maintaining high yield while improving measurement precision.
Solution Approach 2:
The patent implements feedback by measuring the actual output of each device during manufacturing, comparing it to the target value, calculating correction factors, and storing these factors in non-volatile memory for use during normal operation. This closed-loop approach enables continuous improvement of measurement accuracy without reducing manufacturing yield.
2Measurement precision
If measuring output during test and adjusting parameters by laser trimming, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent replaces the mechanical laser trimming process with an electronic/software-based solution. Instead of physically adjusting circuit components, the system measures device output, calculates correction factors, and stores them in non-volatile memory for software compensation, thereby eliminating complex mechanical calibration equipment and processes.
Solution Approach 2:
The patent changes the approach from physical parameter adjustment (laser trimming of resistors) to digital parameter correction. By storing correction factors in non-volatile memory, the system adjusts measurement parameters through software rather than hardware modification, reducing device complexity and manufacturing cost while maintaining precision.
3Measurement precision
If measuring output during test and storing correction factor in non-volatile memory, then measurement precision is improved, but device complexity increases due to additional memory requirements
Solution Approach 1:
The patent applies universality by using the existing non-volatile memory resources already present in the device circuit for the additional function of storing calibration correction factors. Rather than adding dedicated memory components, the system leverages available memory infrastructure, thereby improving measurement precision without proportionally increasing device complexity.
4Ease of manufacture
If calibration is performed only at test, then manufacturing cost is reduced, but reliability deteriorates due to inability to account for aging and temperature effects
Solution Approach 1:
The patent implements continuity of useful action by establishing a calibration mechanism that operates both during manufacturing and during device operation. The system continuously monitors and can re-calibrate based on temperature and aging effects, ensuring ongoing reliability while using cost-effective software-based correction rather than expensive hardware recalibration.
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 consistency and accuracy of ambient light detection, reducing manufacturing costs and enabling continuous calibration for aging and temperature effects, while maintaining simplicity and cost-effectiveness.
Implementation Method 1
at least one light-sensitive pixel comprising a photodiode
Data Source
AI summary
Ambient light is detected by a photodiode circuit by measuring the time taken for a digital output of the photodiode circuit to change state in response to exposure of a photodiode of the photodiode circuit to that ambient light. A nominal time for state change is calculated based on photodiode circuit characteristics. Furthermore, an effective time for the photodiode circuit digital output to change state is determined in a calibration mode where the photodiode has been disconnected and a reference current is applied to the circuit. An illumination value of the detected ambient light is then calculated as a function of: the measured time, the effective time and the nominal time.