Semi-Active Laser Receiver Readout Circuit for Eye-Safe Detection
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Solution Overview
Problem
Existing semi-active laser (SAL) receivers are limited by a 2x2 pixel array size due to cost, size, and power constraints, which restricts resolution and field of view, and use harmful 1.06 micron laser wavelengths, causing eye damage and performance degradation under sunlight exposure.
Innovation Solution
A readout circuit for large focal plane arrays with adaptive photodetector load circuits, trans-impedance amplifiers, comparators, sample and hold rings, and pulse detection logic, enabling efficient readout and eye-safe laser operation without increasing cost or size, using a 32x32 pixel array with 100 MHz sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pixel array size is increased to improve resolution and field of view, then measurement precision and field of view are improved, but device complexity, power consumption, and cost increase prohibitively
Solution Approach 1:
The patent divides the focal plane array into multiple zones or regions, where not all pixels are actively processed at full resolution simultaneously. This segmentation allows the system to maintain high resolution when needed while reducing the number of active ADC circuits during normal operation, thereby lowering complexity and power consumption.
Solution Approach 2:
The system dynamically adjusts the number of active ADC circuits and processing channels based on operational requirements. When high resolution is needed, more ADCs are activated; during normal operation, fewer ADCs are used. This dynamic adaptation allows the system to maintain high measurement precision when needed while keeping device complexity and power consumption manageable during standard operation.
2Measurement precision
If the pixel array size is increased to improve resolution and field of view, then measurement precision and field of view are improved, but power consumption increases prohibitively
Solution Approach 1:
The focal plane array is segmented into multiple zones with different processing priorities. Only the necessary number of pixels and corresponding ADC circuits are activated based on current operational needs, reducing overall power consumption while maintaining high resolution capability when required.
Solution Approach 2:
The system dynamically controls power distribution to ADC circuits and processing channels, activating only the necessary number of channels based on resolution requirements. This dynamic power management enables the system to achieve high resolution when needed while consuming minimal power during normal operation.
3Measurement precision
If the pixel array size is increased to improve resolution and field of view, then measurement precision and field of view are improved, but cost increases prohibitively
Solution Approach 1:
The system uses a large focal plane array but segments it into multiple zones, activating only the necessary number of pixels and ADC circuits for each operation. This approach allows the system to maintain high resolution capability when needed while using a cost-effective number of expensive ADC components, making the overall system more affordable.
Solution Approach 2:
The system dynamically configures the number of active processing channels based on operational requirements, allowing a cost-effective implementation with fewer ADC circuits to achieve high resolution when needed rather than requiring all pixels to be fully processed simultaneously at all times.
4Reliability
If 1.06 micron laser wavelength is used, then existing SAL receiver performance is maintained, but eye damage and sunlight interference occur
Solution Approach 1:
The patent changes the operating wavelength parameter from 1.06 microns to 1.5 microns, which is inherently safer for eye exposure and less affected by sunlight. This parameter change requires corresponding adjustments in the detector sensitivity and optical system design, but ultimately achieves both maintained performance and reduced harmful effects.
Solution Approach 2:
The patent converts the potential disadvantage of operating at a different wavelength into a benefit by selecting 1.5 microns, which naturally provides eye safety and reduced sunlight interference. This wavelength choice transforms what could be seen as a deviation from traditional operation into a protective feature that eliminates harmful effects while maintaining operational effectiveness.
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
Enables high-resolution imaging with large focal plane arrays while using eye-safe lasers, reducing eye damage and sunlight interference, and maintaining cost and size efficiency.
Implementation Method 1
a photodetector for the one pixel and coupled to a frequency dependent circuit
Data Source
Figure 1
AI summary
A circuit for readout from for readout from a focal plane array having a number of pixels, includes, for each one pixel, an adaptive photodetector load circuit (15) coupled to a detector for the one pixel, a trans-impedance amplifier (35), the detector being AC coupled to the trans-impedance amplifier, a comparator component, receiving an AC coupled output of the trans-impedance amplifier and comparing the AC coupled output to a predetermined threshold, a sample and hold ring comprising a number charge storage components connected in parallel, each one charge storage component comprising a capacitor (60) in series with an enabling three point switching component (62) and a pulse detection logic circuit receiving an output of the comparator component.