Single-Slope Comparator Offset Multi-Sampling Speed
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Solution Overview
Problem
CMOS image sensors face a trade-off between high-speed readout and low power consumption, with single-slope ADCs requiring increased clock cycles for multi-sampling, leading to reduced image processing speed and non-linear characteristics due to different ramp signal generation devices for varying illuminance conditions.
Innovation Solution
A single-slope comparison device applies an offset to the input signal to achieve multiple crossings with a ramp signal, allowing for multi-sampling without increasing clock cycles, using an offset generation circuit, comparison circuit, and control circuit to detect crossings and generate offset control signals, thereby enabling energy-efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-sampling is performed by increasing the number of clocks, then noise cancellation performance is improved, but image processing speed is reduced
Solution Approach 1:
The patent changes the parameter of ramp signal slope by using multiple ramp signal generation devices with different slope values (e.g., ×1, ×2, ×4, ×8). This allows multi-sampling to be achieved by varying the slope parameter rather than increasing clock cycles, thereby maintaining processing speed while improving noise cancellation performance through multiple sampling operations.
Solution Approach 2:
The system dynamically selects different ramp signal generation devices based on the input signal level and illuminance conditions. By dynamically adjusting which ramp signal device is used, the system can perform multi-sampling with varying slopes adaptively, achieving both noise reduction and maintained processing speed through dynamic parameter selection rather than static multi-clock operation.
2Productivity
If the slope of the ramp signal is increased by multiple times to perform analog-to-digital conversion, then the number of clocks is reduced, but it becomes more difficult to settle the ramp signal properly
Solution Approach 1:
The patent segments the ramp signal generation function into multiple dedicated devices, each handling a specific slope range (e.g., first device for ×1-×2, second device for ×4-×8). This segmentation allows each device to be optimized for its specific operating range, ensuring proper settling accuracy is maintained while achieving high-speed conversion through appropriate slope selection.
Solution Approach 2:
Different ramp signal generation devices are assigned different local characteristics (slope values) suited for specific signal levels. The system applies the appropriate local quality (slope) based on the input signal characteristics, ensuring that each conversion operation uses the optimal slope for settling accuracy while maintaining overall high conversion speed.
3Measurement precision
If different ramp signal generation devices are used for low illuminance and high illuminance conditions, then noise performance is improved, but non-linear characteristics occur due to characteristic differences between devices
Solution Approach 1:
The system employs feedback mechanisms to detect and compensate for characteristic differences between ramp signal generation devices. By monitoring the output and comparing it against expected linear relationships, the system can apply correction factors or adjust operating parameters to maintain linearity across different devices and illuminance conditions, thereby preserving both noise performance and linear characteristics.
Data Source
AI summary
A comparison device includes an offset generation circuit that includes an input port to receive an offset control signal and is structured to generate an offset based on the received offset control signal; a comparison circuit comprising a first input port coupled to the offset generation circuit to receive a first input signal and a second input port coupled to receive a second input signal that is offset by the offset generated by the offset generation circuit and operable to compare the first input signal with the second input signal to produce a comparison signal; and a control circuit coupled to the comparison circuit to receive the comparison signal and operable to detect a crossing of the first input signal and the second input signal according to the comparison signal circuit and to output the offset control signal to the offset generation circuit.