Digital Focal Plane Array for True High Dynamic Range TDI Imaging
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Solution Overview
Problem
Time-delay-and-integrate (TDI) cameras with charge-coupled device (CCD) image sensors face limitations due to small charge well depth, which restricts their dynamic range, limiting sensitivity and resolution in imaging applications.
Innovation Solution
The use of digital focal plane arrays (DFPAs) with multi-exposure techniques and innovative processing methods to estimate total detections across multiple integration periods, allowing for extended dynamic range and high-resolution imaging by transferring counts non-destructively and leveraging counter rollovers to extend the dynamic range beyond native bit depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CCD-based TDI imaging is used to achieve long exposure times and high SNR, then signal-to-noise ratio is improved, but dynamic range is limited due to small charge well depth
Solution Approach 1:
The patent segments the dynamic range measurement into multiple parts by using multiple counters with different bit depths. The first counter captures the most significant bits of the charge accumulation, while the second counter captures the least significant bits. This segmentation allows the system to measure both very large and very small charge values simultaneously, effectively extending the dynamic range beyond what a single counter could provide while maintaining high SNR through the TDI integration process.
2Object-affected harmful factors
If multi-exposure techniques are used to extend dynamic range, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The patent merges the outputs of multiple counters with different bit depths to create a unified extended dynamic range measurement. The first counter (with more bits) and the second counter (with fewer bits) are combined through a merging circuit that integrates their respective measurements. This merging approach consolidates the complexity into a dedicated circuit rather than requiring complex software processing, thus extending dynamic range while keeping the overall device complexity manageable through hardware integration.
3Object-affected harmful factors
If more counter bits are used to increase dynamic range, then dynamic range is improved, but pixel size increases reducing resolution
Solution Approach 1:
The patent transitions from a single-dimensional approach (one large counter per pixel) to a multi-dimensional approach by stacking multiple counters with different bit depths at the same pixel location. Instead of increasing the bit depth of a single counter horizontally, the system adds vertical dimensionality by layering counters, allowing extended dynamic range measurement without increasing the horizontal pixel footprint. This maintains high image resolution while achieving extended dynamic range through the multi-counter architecture.
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 enables TDI imaging with true high-dynamic range, achieving fast, wide-area imaging with high sensitivity and resolution, suitable for applications like surveillance, commercial inspection, and medical imaging.
Implementation Method 1
generating, in a first m-bit counter in the counter array, a first count of less than or equal to 2m−1. This first count represent detections by a first detector element in the detector array during a first integration period
Data Source
AI summary
In time-delay-and-integrate (TDI) imaging, a charge-couple device (CCD) integrates and transfers charge across its columns. Unfortunately, the limited well depth of the CCD limits the dynamic range of the resulting image. Fortunately, TDI imaging can be implemented with a digital focal plane array (DFPA) that includes a detector, analog-to-digital converter (ADC), and counter in each pixel and transfer circuitry connected adjacent pixels. During each integration period in the TDI scan, each detector in the DFPA generates a photocurrent that the corresponding ADC turns into digital pulses, which the corresponding counter counts. Between integration periods, the DFPA transfers the counts from one column to the next, just like in a TDI CCD. The DFPA also non-destructively transfers some or all of the counts to a separate memory. A processor uses these counts to estimate photon flux and correct any rollovers caused by “saturation” of the counters.