CMOS Image Sensor Readout Circuit Mode Switching
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Solution Overview
Problem
Conventional CMOS image sensor readout circuits face challenges in achieving an optimized balance between image quality and frame rate, as they can only operate in either single-ramp or dual-ramp modes, which have distinct drawbacks.
Innovation Solution
A readout circuit design that includes a sample and hold circuit, analog-digital conversion circuit, first and second memory banks, and an output circuit, allowing it to operate in both single-ramp and dual-ramp modes by generating and processing image data through sequential output or difference calculation, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the readout circuit operates in single-ramp mode, then the frame rate is improved, but the image quality deteriorates
Solution Approach 1:
The readout circuit dynamically switches between single-ramp mode and dual-ramp mode based on operational requirements. The circuit includes mode selection logic that can configure the ramp generator to produce either one ramp signal (single-ramp mode for high frame rate) or two ramp signals (dual-ramp mode for high image quality), enabling adaptive optimization of the trade-off between productivity and measurement precision.
Solution Approach 2:
The invention changes the operational parameters of the readout circuit by adjusting the ramp signal configuration. By modifying the number of ramp cycles and the timing parameters of the ramp generator, the circuit can operate in different modes to prioritize either frame rate (single-ramp) or image quality (dual-ramp with correlated double sampling), thus resolving the contradiction through parameter optimization.
2Measurement precision
If the readout circuit operates in dual-ramp mode, then the image quality is improved, but the frame rate deteriorates
Solution Approach 1:
The readout circuit employs dynamic mode switching capability that allows it to transition between dual-ramp mode (when image quality is prioritized) and single-ramp mode (when frame rate is prioritized). This dynamic adaptability resolves the contradiction by enabling the system to select the appropriate operational mode based on real-time performance requirements.
Solution Approach 2:
The invention optimizes the frame rate in dual-ramp mode by adjusting critical parameters such as ramp signal frequency, sampling timing, and memory bank switching speed. By fine-tuning these parameters, the circuit achieves the best possible frame rate while maintaining the image quality benefits of dual-ramp correlated double sampling, thus resolving the productivity penalty associated with high-precision mode.
3Device complexity
If the readout circuit uses only one ramp mode, then the device complexity is reduced, but the adaptability deteriorates
Solution Approach 1:
The readout circuit is designed with multi-functionality to perform both single-ramp and dual-ramp operations using the same hardware infrastructure. The circuit includes configurable components such as a programmable ramp generator, selectable memory bank configurations, and flexible timing control logic that enable a single device to adapt to different operational requirements without requiring separate dedicated circuits for each mode.
Solution Approach 2:
The invention implements dynamic configurability within the readout circuit through mode selection control logic that can reconfigure the circuit's operational state. This dynamic adaptation allows the same hardware to exhibit different functional behaviors (single-ramp or dual-ramp mode) based on control signals, thereby achieving high adaptability without increasing physical device complexity.
Data Source
AI summary
A readout circuit is provided to generate an image datum representing an image sensed by a sensing array. The readout circuit includes a sample and hold circuit, an analog-digital conversion circuit, first and second memory banks, and an output circuit. The sample and hold circuit performs a sample and hold operation on at least one output signal from the sensing array to generate first and second sample-hold signals. The analog-digital conversion circuit generates first and second output datums according to the first and second sample-hold signals respectively. When the readout circuit operates in a first mode, the output circuit outputs the first and second output datums, received from the first and second memory banks, sequentially to serve as the image datum. When the readout circuit operates in a second mode, the output obtains difference between the first and second output datums to serve as the image datum.