Multi-Tap CCD Gain Correction via Digital PID Loop
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Solution Overview
Problem
Multi-tap CCD cameras exhibit inherent response errors due to PVT variations, leading to 'split screen' visual effects and gain/black level differences between readout paths, which conventional calibration methods struggle to fully address, resulting in residual gain errors of several digital counts.
Innovation Solution
Implementing a 'one shot' level correction and continuous PID gain correction control loop that measures gradients at the tap seam, filters scene-based gradients, and selectively enables gain correction based on scene motion, allowing for tighter gain matching without masking the CCD sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-point or multi-point factory calibration is performed, then level calibration can be achieved, but gain errors remain at several digital counts due to limited control resolution and PVT variance
Solution Approach 1:
The patent implements a continuous dynamic gain correction control loop that continuously monitors and adjusts gain errors in real-time, rather than relying on static factory calibration. The system dynamically adapts to PVT variations by continuously measuring gradients at the tap seam and adjusting correction values, enabling gain matching precision of one digital count or less.
Solution Approach 2:
The patent employs a feedback control mechanism where the system continuously measures the gradient at the tap seam between adjacent segments, compares it against reference values, and adjusts gain correction values accordingly. This closed-loop feedback approach enables continuous refinement of gain matching, achieving precision of one digital count or less by constantly compensating for PVT variations.
2Extent of automation
If automated tap balance is performed by controlling the analog to digital converter dynamically, then level calibration can be achieved, but gain resolution is limited by control resolution and PVT variance
Solution Approach 1:
The patent moves the correction mechanism from the analog domain (analog to digital converter controls) to the digital domain (digital correction values applied after conversion). By performing gain correction in the digital domain, the system achieves higher effective resolution since digital values can represent gain adjustments with precision beyond the limitations of analog control resolution, achieving one digital count or less error.
3Measurement precision
If level calibration is performed, then black level differences can be corrected, but the CCD sensor must be shrouded which increases device complexity
Solution Approach 1:
The patent enables the system to perform its own calibration using real-time scene data without requiring external masking devices or shrouds. The continuous gain correction mechanism uses the actual imaging scene to measure gradients and compute correction values, making the calibration process self-sufficient and eliminating the need for additional hardware components.
Solution Approach 2:
The patent incorporates calibration functionality directly into the normal operation of the camera system, performing gain correction continuously as images are captured. This eliminates the need for separate pre-calibration steps that would require masking, as the system prepares and maintains calibration readiness through continuous operation rather than requiring preliminary setup actions.
4Manufacturing precision
If digital image processing performs contrast-enhancing and peaking operations, then image quality is improved, but errors between pixels from each path are increased
Solution Approach 1:
The patent applies gain correction values to equalize the response of adjacent segments before contrast-enhancing and peaking operations are performed on the combined image data. By pre-correcting the segment mismatches, the subsequent image processing operations work on already-balanced data, preventing the amplification of path errors and maintaining both image quality and path matching accuracy.
Data Source
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AI summary
According to one aspect, embodiments herein provide a CCD sensor comprising a pixel array having a first segment configured to produce a first tap signal responsive to receipt of electromagnetic radiation from a scene to be imaged, a second segment configured to produce a second tap signal responsive to receipt of the electromagnetic radiation from the scene, a region of interest including a portion of the first segment adjacent the second segment and a portion of the second segment adjacent the first segment, and a processor configured to receive the first and second tap signals, perform level correction on one of the first and second tap signals based on magnitudes of the first and second tap signals, and perform gain correction on one of the first and second tap signals based on a comparison between magnitudes of the first and second tap signals corresponding to the region of interest.