CMOS Sensor Gain Control with Analog-Digital Calibration Feedback
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Solution Overview
Problem
CMOS sensor imagers face non-uniform operation due to variations in fabrication processes and environmental changes, leading to limited gain precision and chip-to-chip dispersion, which is exacerbated by the use of conventional analog amplifiers that struggle with fine gain step sizes required for high-performance applications.
Innovation Solution
A system combining analog and digital gain, where digital amplifiers calibrate and compensate for the limitations of analog amplifiers, providing fine step sizes and high precision by using a feedback component to adjust gain based on actual and nominal gain comparisons, thereby optimizing dynamic range and noise performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If analog amplifiers with selectable analog capacitors are used to provide gain control, then gain range and dynamic range are optimized, but gain precision and uniformity deteriorate due to fabrication variations and limited capacitor precision
Solution Approach 1:
The gain control function is segmented into two independent parts: analog gain control for coarse adjustment and dynamic range optimization, and digital gain control for fine adjustment and precision. This segmentation allows each part to specialize - analog handles the bulk gain range while digital provides the precise steps, eliminating the trade-off between range and precision that plagues unified analog systems.
Solution Approach 2:
A digital-to-analog converter (DAC) serves as an intermediary component that bridges the digital and analog domains. The DAC converts precise digital gain values into analog signals that can be applied to the sensor output, enabling digital precision to control analog gain without requiring physically precise analog capacitors for every gain step.
2Ease of operation
If analog step size is reduced to provide finer gain steps (e.g., from 3 dB to 0.1 dB), then gain granularity is improved, but analog capacitor precision and monotonic behavior deteriorate
Solution Approach 1:
The patent replaces the mechanical/analog capacitor-based gain control system with a digital control system for fine gain steps. Instead of relying on physically adjustable analog capacitors with limited precision, the system uses digital signal processing with 12-bit or higher resolution to achieve 0.1 dB or finer gain steps, eliminating the fundamental limitations of analog capacitor precision and monotonicity.
Solution Approach 2:
The patent transitions from a one-dimensional analog control approach to a two-dimensional approach combining analog and digital domains. The analog domain provides the primary gain control while the digital domain adds a second dimension of precision control, allowing fine gain steps to be achieved through digital processing rather than analog component precision.
3Use of energy by moving object
If conventional analog amplifiers are used to provide gain control, then dynamic range is optimized, but chip-to-chip uniformity and monotonic behavior deteriorate due to fabrication tolerances
Solution Approach 1:
The patent implements a feedback mechanism where the actual gain of each analog amplifier is measured and stored as a calibration value. During operation, the digital gain control uses these calibration values to compensate for analog amplifier variations, ensuring that each chip operates with the intended gain characteristics despite fabrication tolerances. This feedback loop eliminates the need for perfectly matched analog components.
Solution Approach 2:
The patent changes the operating parameters from purely analog to a hybrid analog-digital system. By introducing digital gain control with high bit resolution (12-bit or higher), the system can precisely adjust the gain in small increments to compensate for analog amplifier variations. This parameter change from analog-only to hybrid control enables chip-to-chip uniformity without sacrificing dynamic range.
Data Source
AI summary
The claimed subject matter provides systems and/or methods that facilitate combining analog and digital gain for utilization with CMOS sensor imagers. The analog gain can provide coarse gain steps and the digital gain can provide finer gain steps between adjacent coarse analog gain values. Further, since analog gain can suffer from low precision, dispersion, etc., on-chip calibration can be implemented to calibrate the analog and digital gain. For example, a digital amplifier can be calibrated to compensate for differences between actual and nominal analog gains associated with one or more analog amplifiers.