Light-to-Frequency Converter Circuit for Low Light Sensitivity
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Solution Overview
Problem
Existing light-to-frequency converters face challenges in achieving high effective resolution at low light levels, particularly in spectroscopy applications with low intensity narrow band sources, often resulting in saturation and reduced sensitivity.
Innovation Solution
A circuit arrangement that detects electromagnetic energy by generating a sequence of events based on the energy level, measuring the time period until a given number of events is generated, and providing this time period as an output, using a non-fixed time integrating feedback loop and digital circuitry to improve resolution without increasing die area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If analog gain is increased to improve low light sensitivity, then low light sensitivity is improved, but saturation occurs at a lower light level
Solution Approach 1:
The patent applies dynamics by making the integration time variable rather than fixed. The integration time is dynamically adjusted based on the detected light level: longer integration times are used for low light levels to improve sensitivity, while shorter integration times are used for high light levels to prevent saturation. This dynamic adaptation allows the system to maintain optimal performance across a wide range of light conditions without requiring multiple fixed-gain stages.
2Measurement precision
If diode area is increased to improve low light sensitivity, then low light sensitivity is improved, but device area increases
Solution Approach 1:
The patent applies parameter changes by modifying the integration time parameter rather than the physical diode area. By extending the integration time, the system accumulates more signal from the same diode area, effectively improving low light sensitivity without increasing the physical device area. This parameter-based solution maintains a compact device footprint while achieving the desired sensitivity improvement.
3Device complexity
If conventional fixed time counting is used, then device complexity is low, but measurement precision is reduced due to quantization uncertainty
Solution Approach 1:
The patent applies inversion by reversing the conventional counting approach. Instead of counting the number of events within a fixed time interval (which introduces quantization uncertainty), the system measures the time required to accumulate a fixed number of events. This inverted approach eliminates the quantization uncertainty associated with fixed-time counting, as the measurement is limited only by the clock resolution rather than the event distribution within a fixed interval.
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 effective resolution of light-to-frequency converters for low light conditions, providing finer resolution and reducing saturation issues, while maintaining the maximum light digitalization capacity without increasing die area.
Implementation Method 1
Detecting electromagnetic energy may comprise converting the electromagnetic energy into a current, which may be achieved by means of a photodiode
Data Source
Figure 1~2
Figure 3
AI summary
A circuit arrangement comprises a photo detector (2) for detecting electromagnetic energy and a signal generating means (4, 6, 12, 16) being suitable for generating a sequence of events wherein an event interval of the sequence depends on the detected electromagnetic energy. The signal generating means (4, 6, 12, 16) is coupled downstream of the photo detector (2). A counting means (30, 32, 34, 36) for measuring a time period until a given number of events has been generated is coupled downstream of the signal generating means (4, 6, 12, 16).