Imaging Array Dual Gain Digitization Circuit Dynamic Range
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Solution Overview
Problem
Current CMOS imaging arrays face challenges in achieving high dynamic range due to high digitization noise at low light levels, which masks low-level signals, and using high N-value ADCs is impractical due to increased readout time and cost considerations.
Innovation Solution
Implementing a dual gain digitization circuit with two ADCs and amplifiers, where the effective conversion gain is set based on the signal level, allowing selection of the appropriate output to maintain digitization noise as a small fraction of shot noise, thereby enhancing dynamic range without requiring high N-value ADCs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high gain amplifier is used in digitization circuit to reduce quantization noise for low light levels, then measurement precision is improved, but the output voltages become too high for conventional CMOS circuitry to process
Solution Approach 1:
The pixel array is divided into two separate arrays: first pixel sensors for low light levels with high gain amplification, and second pixel sensors for high light levels with low gain amplification. This segmentation allows each array to be optimized for its specific light level range, resolving the contradiction between noise reduction and voltage level management.
Solution Approach 2:
Different gain settings are applied locally to different pixel arrays based on their intended operating conditions. The first array uses high gain specifically for low light detection, while the second array uses low gain for high light detection, allowing each region to have the quality needed for its specific function.
2Object-generated harmful factors
If low gain amplifier is used to maintain signal within CMOS circuitry range for high intensity pixels, then device compatibility is improved, but quantization noise masks low level signals
Solution Approach 1:
The pixel array is segmented into two distinct arrays, each with amplifiers optimized for their respective gain requirements. This allows low gain amplifiers to be used where needed without compromising low light detection, as a separate high gain array handles that function.
Solution Approach 2:
The gain parameter of the amplifiers is changed based on the light level conditions. High gain is applied for low light levels to amplify weak signals above quantization noise, while low gain is applied for high light levels to keep signals within CMOS circuitry processing range.
3Measurement precision
If dual gain digitization circuit with two ADCs is implemented, then dynamic range is improved, but device complexity increases
Solution Approach 1:
Instead of using a single complex dual-ADC circuit for all pixels, the system segments the pixel array into two separate arrays, each with its own ADC optimized for its gain setting. This distributes the complexity across multiple simple units rather than concentrating it in one complex unit.
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 effectively reduces digitization noise at low light levels, allowing for improved dynamic range without increasing readout time or costs, ensuring that digitization noise is always a small fraction of shot noise, thus enhancing the imaging array's performance.
Implementation Method 1
each pixel includes a photodetector that measures the amount of light that falls on some portion of the pixel area
Implementation Method 2
an amplifier that sets the effective gain of the analog-to-digital converter
Implementation Method 3
the signal on that bit line is digitized with an analog-to-digital converter
Data Source
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AI summary
An image sensor and a method for using the same are disclosed. The image sensor[40] includes an array of pixel sensors[41], a signal digitizing circuit[48], and a digitizing controller[53]. The array of pixel sensors includes a plurality of pixel sensors. Each pixel sensor includes a photodetector[46], a charge conversion circuit[34], and a gate transistor[36]. The charge conversion circuit generates a voltage signal that is related to a charge on the photodiode, and the gate transistor couples the voltage signal to a bit line[43] in response to a first signal. The signal digitizing circuit converts the voltage signal to a plurality of output digital values. Each output digital value has a different level of digitization noise. One of the output digital values is selected for output in response to an output selection signal that is generated by the digitizing controller.