SWIR Photodetector Timing to Limit Dark Current Noise
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Solution Overview
Problem
Existing SWIR imaging systems face challenges with high dark current in photodiodes, which affects the quality of detection signals and are often expensive to manufacture, limiting their integration into electronics and manufacturing capacity.
Innovation Solution
An active SWIR imaging system using Germanium photodiodes with a pulsed illumination source and a passively Q-switched laser, along with a controller to manage integration time and reduce dark current noise, and a method to compensate for dark current effects using voltage-controlled current circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Germanium photodiodes are used for SWIR imaging, then detection capability in SWIR range is improved, but dark current increases significantly
Solution Approach 1:
The patent employs pulsed illumination to activate the photodiodes only during specific time intervals, allowing the system to capture SWIR signals while minimizing dark current accumulation. The integration time is controlled to be shorter than the dark current relaxation time constant, effectively reducing dark current noise while maintaining detection capability.
Solution Approach 2:
The patent changes the operational parameters of the photodiodes by controlling the integration time and bias voltage. By optimizing these parameters, the system achieves a balance between detecting SWIR signals and minimizing dark current effects, allowing Germanium photodiodes to function effectively despite their inherently high dark current.
2Measurement precision
If InGaAs-based photodiodes are used for SWIR imaging, then detection performance is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent utilizes Germanium photodiodes which are cheaper and easier to manufacture than InGaAs-based photodiodes. Although Germanium photodiodes have higher dark current, the patent compensates for this through pulsed illumination and optimized integration timing, making the overall system more cost-effective while maintaining acceptable detection performance.
Solution Approach 2:
By changing the operational parameters (integration time, illumination pulse duration) to match the dark current characteristics of Germanium photodiodes, the patent enables the use of cheaper photodiode materials without sacrificing detection performance, thereby reducing manufacturing costs.
3Measurement precision
If integration time is increased to improve signal detection, then detection sensitivity is improved, but dark current noise accumulation increases
Solution Approach 1:
The patent uses periodic pulsed illumination with controlled duty cycles to activate the photodiodes only when needed for signal detection. This periodic operation allows the system to accumulate sufficient signal while limiting the total integration time to prevent excessive dark current noise accumulation.
Solution Approach 2:
The patent applies partial integration by using integration times that are shorter than the dark current relaxation time constant. This partial action approach accumulates enough signal for detection while deliberately limiting the integration duration to prevent excessive dark current noise, achieving an optimal balance between sensitivity and noise.
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
The system achieves improved signal-to-noise ratio by limiting dark current noise, reducing the impact of dark current on detection signals, and provides a cost-effective solution for SWIR imaging, enhancing integration into electronic systems and manufacturing efficiency.
Implementation Method 1
an imaging receiver comprising a plurality of Germanium (Ge) PDs operative to detect the reflected SWIR radiation, wherein the imaging receiver produces for each Ge PD a respective detection signal representative of the reflected SWIR radiation impinging on the respective Ge PD
Implementation Method 2
a passively Q-switched laser
Data Source
AI summary
Electro-optical (EO) systems comprising a photodetector array (PDA) comprising a plurality of photosites (PSs), each PS operative to output detection signals for different frames, the detection signal output for a frame by the respective PS being indicative of an amount of light impinging on the respective PS during a respective frame exposure time (FET); a usability filtering module operative to first determine for each PS that the PS is unusable based on a first FET, and to later determine that the PS is usable based on a second FET that is shorter than the first FET; and a processor operative to generate images based on frame detection levels of the plurality of PSs.