Optical Sensor Conversion Using Residual Charge Measurement
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Solution Overview
Problem
Existing light-to-digital converters using photodiodes have limited resolution due to neglecting residual charge at the end of measurement cycles, which restricts the maximum light level that can be measured without saturation.
Innovation Solution
A method that measures residual charge on the photodiode integrator using a successive approximation search algorithm, incorporating a precharge phase for error correction and employing larger capacitors during the residue phase to enhance resolution without extending integration time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the charge packet size is reduced to improve resolution, then measurement precision is improved, but the maximum light level that can be measured without saturation is reduced
Solution Approach 1:
The conversion process is divided into multiple segments: coarse integration phase for capturing total charge and fine residue phase for measuring remaining charge. This segmentation allows the system to achieve high resolution without reducing the maximum measurable light level, as each phase handles different portions of the measurement range.
Solution Approach 2:
The integration capacitor is pre-charged to a reference voltage level before the measurement begins. This preliminary action establishes a known starting point that allows the system to measure both small and large light intensities accurately, preventing saturation while maintaining resolution.
2Measurement precision
If the integration time is extended to improve resolution, then measurement precision is improved, but the measurement speed is reduced
Solution Approach 1:
The measurement is performed in periodic phases: a coarse integration phase followed by a faster residue measurement phase. This periodic structure allows the system to achieve high resolution through the integrated charge measurement while maintaining speed by quickly measuring only the residual charge in the second phase.
Solution Approach 2:
The majority of the measurement is performed in advance during the integration phase, capturing the bulk of the charge information. The subsequent residue phase only needs to measure the remaining small amount of charge, significantly reducing the time required for high-precision measurement.
3Device complexity
If residual charge is neglected to simplify the conversion process, then device complexity is reduced, but measurement accuracy is reduced
Solution Approach 1:
The residual charge, which is typically a small and difficult-to-measure component, is extracted and measured separately in a dedicated residue phase. This extraction allows the main integration phase to focus on capturing the total charge while the residue phase specifically addresses the previously neglected residual component, improving accuracy without significantly increasing overall complexity.
Solution Approach 2:
The residue measurement acts as an intermediary step that bridges the gap between coarse integration and fine measurement. By introducing this intermediate measurement phase, the system can accurately account for residual charge that would otherwise be lost, improving measurement accuracy while keeping the overall process manageable.
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 increases the effective resolution of light measurement without reducing the maximum light level that can be processed, providing improved accuracy by accounting for residual charge.
Implementation Method 1
a photodiode (1)
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An optical sensor arrangement comprises a photodiode and a converter arrangement including an integration amplifier (2), a comparator amplifier (3), an integration capacitor (CINTH) and a result register (6).During a precharge phase the result register (6) is set to a starting value. During an integration phase a current is sampled through the photodiode (1) to update the result register (6) in response to down charges applied to an input of the integration amplifier. During a residue phase the result register (6) is updated in dependence on the charge remaining on the integration capacitor (CINTH). Measuring the residual charge increases resolution and accuracy of the converter.