Black Level Calibration Circuit With Inverse Gain Feedback
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Solution Overview
Problem
Existing black level calibration circuits in image signal processing are complex and resource-intensive, particularly in integrated circuits, due to the need for a high-gain feedback loop that requires a complex inverse amplifier to maintain stability and compensate for varying amplifier gains, leading to increased chip area and production overheads.
Innovation Solution
A circuit with an analogue gain amplifier, analogue-to-digital converter, and digital-to-analogue converter forming a feedback loop, where an inverse gain circuit maintains the loop gain within predetermined bounds, allowing for automatic adjustment to stabilize the loop and reduce complexity, using a programmable gain amplifier and a look-up table to select inverse gain factors based on amplifier coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-gain feedback loop is used for black level calibration, then calibration accuracy is improved, but device complexity increases due to the need for a complex inverse amplifier
Solution Approach 1:
The patent applies dynamics by making the amplifier gain programmable and adjustable through a control register, allowing the system to adapt its gain settings dynamically. This enables the feedback loop to maintain stability across varying gain conditions without requiring a complex fixed inverse amplifier, thus improving calibration accuracy while managing device complexity through software-controlled adaptability.
Solution Approach 2:
The patent changes the gain parameter of the amplifier to be programmable rather than fixed, allowing different gain values to be selected based on calibration needs. This parameter change enables the system to achieve high calibration accuracy when needed while operating in simpler modes during normal operation, effectively resolving the contradiction between calibration precision and overall system complexity.
2Stability of the object's composition
If a complex inverse amplifier is used to maintain feedback loop stability, then loop stability is improved, but chip area increases
Solution Approach 1:
The patent extracts the inverse amplifier function from the analog domain and implements it in the digital domain through a control register and programmable gain amplifier. This separation allows the feedback loop stability to be maintained through digital control mechanisms rather than requiring a complex analog inverse amplifier circuit, thereby reducing the chip area occupied by analog components while preserving loop stability.
Solution Approach 2:
The patent substitutes the mechanical/analog inverse amplifier system with a digital control system. Instead of using a complex analog inverse amplifier circuit to maintain stability, the system uses digital programming and control registers to adjust the amplifier gain, replacing the need for complex analog compensation circuits and reducing overall chip area.
3Device complexity
If a programmable gain amplifier with inverse gain circuit is used, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements self-service through an automatic calibration mode that uses black level pixels from the sensor to automatically determine and set the appropriate gain values. This self-calibrating mechanism reduces the need for complex manual calibration procedures and minimizes the impact of manufacturing variations, as the system automatically adjusts its gain settings based on actual sensor performance rather than relying on precise manual calibration during manufacturing.
Data Source
AI summary
A calibration circuit and method suitable for black level calibration in image processing, the circuit comprising an analogue gain amplifier, an analogue to digital converter; a correction circuit for receiving a digital signal and providing a digital offset signal; and a digital to analogue converter for receiving said digital offset signal and feeding a corresponding analogue offset signal back to the input of said gain amplifier. The calibration circuit is arranged such that the correction circuit and said digital to analogue converter form a feedback loop applying an offset to said input signal and said correction circuit includes an inverse gain circuit for applying an inverse gain to a signal within said correction circuit prior to said digital to analogue converter. Preferably the inverse gain applied is such that the total loop gain does not deviate too far from unity.