Optical Sensor ADC Offset Calibration for Weak Light Accuracy
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Solution Overview
Problem
Existing optical sensor arrangements face challenges in achieving high accuracy, especially under weak light conditions, due to factors like parasitic charge injections and comparator input offsets, which affect the precision of light sensing in applications such as ambient light sensing in consumer electronics.
Innovation Solution
The optical sensor arrangement incorporates a digital-to-analog converter to control the comparator's offset, a reference capacitor circuit to balance charges, and a control logic system that adjusts the switching point of the comparator, ensuring improved accuracy by maintaining a constant analog input signal during the measuring phase and using multiple integrating capacitors for high sensitivity and sub-count digitization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical sensor arrangement uses a standard comparator without offset control, then the device complexity is reduced, but the measurement precision deteriorates due to comparator input offsets affecting weak light detection accuracy
Solution Approach 1:
A digital-to-analog converter (DAC) is introduced as an intermediary component between the digital domain and the analog comparator. The DAC generates an analog offset signal that is fed to the comparator's control terminal, allowing precise control of the comparator's switching point. This intermediary component enables accurate compensation for comparator input offsets and parasitic charges, thereby improving measurement precision without excessively increasing device complexity.
Solution Approach 2:
The invention dynamically adjusts the comparator's offset parameter through the DAC during a calibration phase. By changing the analog input signal to the DAC, the comparator's switching point is precisely controlled to compensate for offsets. This parameter adjustment approach allows the system to adapt to varying conditions and maintain high measurement accuracy for weak light detection.
2Measurement precision
If the optical sensor arrangement operates during a calibration phase before measuring, then the measurement precision is improved by determining the correct switching point, but the productivity is reduced due to the additional time required for calibration
Solution Approach 1:
The system performs a calibration phase before the actual measuring phase to determine the correct switching point of the comparator. During this preliminary action, the DAC is adjusted to compensate for comparator offsets and parasitic charges. Although this adds initial time, it ensures that subsequent measurements are highly accurate, especially for weak light conditions. The calibration is performed once or periodically, minimizing the impact on overall productivity.
Solution Approach 2:
The calibration process can be performed periodically or at scheduled intervals rather than continuously. This allows the system to alternate between calibration phases (for precision) and measuring phases (for productivity). The periodic calibration ensures that the comparator remains accurately tuned over time without continuously sacrificing measurement time, thus balancing precision and productivity requirements.
3Shape
If the optical sensor arrangement is buried underneath dark glass for aesthetic purposes, then the appearance is improved, but the measurement precision deteriorates due to reduced light transmission and increased parasitic effects
Solution Approach 1:
The invention converts the harmful effects of burying the sensor under dark glass (reduced light transmission, increased parasitic charges) into a manageable situation through active compensation. The DAC-controlled comparator offset adjustment compensates for the additional parasitic charges and signal attenuation caused by the dark glass. By measuring and compensating for these specific conditions, the system maintains high measurement precision despite the aesthetically motivated embedding that would normally degrade performance.
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 configuration enhances the accuracy of light sensing by minimizing the impact of parasitic charge injections and comparator offsets, resulting in improved digitization resolution and accuracy in ambient light detection, even under low light conditions.
Implementation Method 1
an optical sensor arrangement comprises a photodiode and an analog-to-digital converter
Data Source
AI summary
An optical sensor arrangement comprises a photodiode (11) and an analog-to-digital converter (12). The analog-to-digital converter (12) comprises an integrator (13) having an integrator input (15) coupled to the photodiode (11), a comparator (14) having a first input coupled to an output of the integrator (13) and a digital-to-analog converter (39) coupled to a control terminal of the comparator (14).