Optical Sensor ADC 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 such as parasitic charge injections and comparator input offsets, which affect the precision of light sensing.
Innovation Solution
The optical sensor arrangement incorporates a digital-to-analog converter to control the comparator's offset during a calibration phase, maintaining a constant analog input signal during the measuring phase, and utilizes a reference capacitor circuit to balance charges, thereby improving accuracy by adjusting the comparator's switching point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical sensor arrangement uses a conventional comparator without offset control, then the device complexity is reduced, but the measurement precision deteriorates due to comparator input offsets affecting light sensing accuracy
Solution Approach 1:
The patent applies preliminary action by performing offset calibration before the actual light sensing measurement. A digital-to-analog converter is used to generate a calibration signal that compensates for comparator offsets in advance, ensuring accurate measurements without requiring complex real-time correction mechanisms during the measurement phase.
Solution Approach 2:
The patent introduces a digital-to-analog converter as an intermediary component between the digital control system and the analog comparator. This mediator enables precise control of the comparator's switching point by converting digital calibration codes into analog voltages, thereby improving measurement precision without directly modifying the comparator's internal structure.
2Illumination intensity
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 intensity reaching the sensor
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the integrator's integration time and the comparator's reference voltage levels to optimize sensitivity for weak light conditions. The system adapts its operating parameters based on the actual light intensity, enabling accurate measurement even when the sensor is positioned under dark glass with limited light transmission.
3Measurement precision
If the optical sensor arrangement uses parasitic charge injection compensation techniques, then the measurement precision is improved, but the device complexity increases due to additional circuit components
Solution Approach 1:
The patent merges the parasitic charge compensation function with the existing calibration circuitry. The same digital-to-analog converter used for offset calibration also serves to compensate for parasitic charge injections by adjusting the comparator's switching point, thereby improving measurement precision without adding separate compensation circuits.
Solution Approach 2:
The patent implements self-service by designing a calibration system that automatically characterizes and compensates for its own parasitic effects. The calibration routine measures the actual behavior of the integrator and comparator, including parasitic charge injections, and uses this information to adjust the measurement process, eliminating the need for external compensation circuits.
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 light sensing by minimizing the impact of parasitic charge injections and comparator offsets, resulting in improved digitization resolution and first count accuracy.
Implementation Method 1
an optical sensor arrangement (10) comprises a photodiode (11) and an analog-to-digital converter (12)... generating a sensor current by a photodiode (11)
Data Source
Figure 1A
Figure 1B
Figure 2A
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).