Pixel Array Coarse Digitization for Local Sensitivity Control
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Solution Overview
Problem
Conventional infrared focal-plane arrays face challenges in digitizing input signals close to the pixel location and independently adjusting sensitivity of active imaging circuits based on ambient illumination conditions, leading to suboptimal performance across different pixels.
Innovation Solution
Incorporating a flash analog-to-digital converter within each pixel to process analog imaging signals into coarse digitized signals, which are then used to adjust the sensitivity of active imaging circuits, thereby improving sensitivity and reducing noise by propagating both signals outside the pixel array for further processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If digitization circuit is placed outside the pixel array, then device complexity is reduced, but measurement precision deteriorates due to signal degradation during transmission
Solution Approach 1:
The pixel array is segmented into multiple subarrays, with each subarray having its own dedicated digitization circuit. This allows digitization to occur close to the photodetectors (improving measurement precision) while keeping each individual digitization circuit simple (managing device complexity through distributed architecture).
Solution Approach 2:
The patent introduces a hierarchical structure where pixel arrays are organized into subarrays, adding a spatial dimension to the architecture. This allows digitization circuits to be positioned at the subarray level rather than requiring every pixel to have full digitization capability, balancing precision and complexity across different spatial scales.
2Device complexity
If global sensitivity control is used for active imaging circuits, then device complexity is reduced, but adaptability deteriorates because different pixels experience different ambient illumination conditions
Solution Approach 1:
The patent implements local sensitivity control where each pixel's active imaging circuit can independently adjust its sensitivity based on local ambient illumination conditions. This is achieved by using the coarse digitized signal from each pixel to control the gain of its own active imaging circuit, allowing each pixel to adapt to its specific lighting environment rather than using a single global sensitivity setting.
Solution Approach 2:
A feedback mechanism is implemented where the coarse digitized signal from each pixel is fed back to control the gain of its corresponding active imaging circuit. This closed-loop control allows the system to automatically adjust sensitivity based on actual measured conditions, improving adaptability while maintaining manageable complexity through local feedback rather than complex global control.
3Measurement precision
If coarse digitization is performed within each pixel, then measurement precision improves, but device complexity increases due to additional circuitry in each pixel
Solution Approach 1:
The digitization function is segmented and distributed to subarray levels rather than requiring full digitization capability in every individual pixel. Each subarray contains dedicated digitization circuits that serve multiple pixels, reducing the complexity burden on individual pixels while maintaining the precision benefits of local digitization.
Solution Approach 2:
The patent implements coarse digitization (partial action) within pixels to capture the most significant bits of the signal, then uses dedicated digitization circuits at the subarray level to complete the full digitization. This partial digitization approach provides sufficient precision for sensitivity control while avoiding the full complexity burden of complete digitization in every pixel.
Data Source
AI summary
A pixel of a pixel array is provided. The pixel includes a low frequency path configured to receive an input signal from a corresponding photodetector. The low frequency path includes a passive imaging circuit provided along the low frequency path, the passive imaging circuit configured to output an analog imaging signal and a flash analog to digital converter (ADC) that receives the analog imaging signal and processes the analog imaging signal to output a coarse digitized signal.