Time Domain Sampling CMOS Imager Wide Dynamic Range
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Solution Overview
Problem
Conventional CMOS imagers operating in the voltage domain face limitations in achieving wide dynamic range and reasonable resolution, with existing techniques suffering from issues like fixed pattern noise, high power consumption, and complex reconstruction processes.
Innovation Solution
A time domain sampling technique that provides two degrees of freedom by varying integration time and reference voltage, allowing for non-uniform sampling patterns to enhance dynamic range and resolution, enabling flexible and programmable imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage domain sampling is used in conventional CMOS imagers, then the imaging function is achieved, but the dynamic range is limited and resolution is insufficient
Solution Approach 1:
The patent changes the sampling domain from voltage to time, and introduces two variable parameters (integration time and reference voltage) to achieve wide dynamic range. By varying these parameters non-uniformly, the system captures 120 dB dynamic range with reasonable resolution without requiring complex additional hardware
Solution Approach 2:
The patent employs dynamic adjustment of integration time and reference voltage during the sampling process. Rather than using fixed sampling parameters, the system adaptively varies these parameters to optimize the capture of different light intensities, enabling both high dynamic range and good resolution
2Measurement precision
If logarithmic response technique is used to improve dynamic range, then dynamic range is enhanced, but fixed pattern noise increases due to device mismatches
Solution Approach 1:
The patent replaces the logarithmic compression mechanism at the photodiode level with a time-domain sampling approach. Instead of using logarithmic response circuits that are sensitive to device mismatches, the system uses linear photodiodes with variable integration times and reference voltages, eliminating the fixed pattern noise issue while maintaining wide dynamic range capability
3Measurement precision
If multiple frame capture technique is used to increase pixel dynamic range, then dynamic range is improved, but power consumption increases and reconstruction processing becomes complex
Solution Approach 1:
The patent implements periodic sampling within a single frame by varying the integration time and reference voltage across different sampling intervals. This approach achieves multiple dynamic range levels in one frame rather than requiring multiple frames, thereby reducing power consumption and eliminating the need for complex inter-frame reconstruction processing
4Measurement precision
If floating-point pixel-level ADC imagers are used to achieve wide dynamic range, then dynamic range is enhanced, but memory requirements increase and reconstruction processing becomes complex
Solution Approach 1:
The patent extracts the dynamic range information into the time domain by measuring the time at which pixel values cross a reference threshold. Instead of storing full floating-point pixel values that require large memory, the system stores time values that are much more compact, achieving wide dynamic range with minimal memory requirements and simple reconstruction
5Measurement precision
If non-uniform sampling pattern is implemented to enhance resolution, then resolution is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal control mechanism that manages both integration time and reference voltage variations through a single non-uniform sampling pattern generator. This multi-functional approach achieves enhanced resolution without proportionally increasing device complexity, as the same control logic governs both variable parameters
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
The technique achieves a wide dynamic range of up to 120 dB and reasonable resolution by aggregating the dynamic ranges of integration time and reference voltage, overcoming the limitations of conventional CMOS imagers and reducing power consumption.
Implementation Method 1
A CMOS type image sensor includes a photodiode or phototransistor employed as a light detecting element
Data Source
AI summary
A time domain sampling technique for a CMOS imager enables a wide dynamic range and flexibility by employing up to two-degrees of freedom during such sampling. Two degrees of freedom can be achieved by making one or both of an integration time and a reference (e.g., voltage or current) variable during sampling. The sampling (or image capture) is implemented by associating a time with when a pixel has a desired value relative to the reference in response to the pixel receiving incident light. The reference can be fixed or variable during different portions of the sampling, and further can be programmable to implement a desired sampling pattern for a given application.