CMOS Image Sensor Ramp-Slope Selection for Fast High-Resolution ADC
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing CMOS image sensors face challenges in achieving high-speed readout and high resolution due to variations in manufacturing elements of comparators, leading to errors in analog-to-digital (AD)-converted data, and difficulties in increasing circuit area and power consumption.
Innovation Solution
The imaging apparatus employs a comparator unit that compares pixel signals with time-dependent ramp signals, using a selecting circuit to determine the appropriate ramp signal slope based on signal amplitude, allowing for bit-shifting to achieve multiple-bit AD conversion with a small number of bits, thereby reducing noise and increasing resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple comparators are used to achieve high-speed readout and high resolution, then AD conversion speed and resolution are improved, but circuit area and power consumption increase
Solution Approach 1:
The patent divides the AD conversion process into multiple stages, using a single comparator sequentially for different signal ranges. The signal is first compared against a threshold to determine if it exceeds a certain level, then further comparison is performed only if needed. This segmentation allows high-resolution conversion without requiring multiple comparators to operate simultaneously, thus reducing circuit area while maintaining conversion precision.
Solution Approach 2:
The patent employs dynamic selection of comparison modes based on the input signal characteristics. The system adapts its comparison strategy by selecting different reference signals and comparison sequences depending on the signal amplitude and required precision. This dynamic approach allows a single comparator to perform the work of multiple fixed comparators, reducing hardware requirements while maintaining high conversion resolution.
2Measurement precision
If multiple comparators are used to achieve high-speed readout and high resolution, then AD conversion speed and resolution are improved, but power consumption increases
Solution Approach 1:
The patent segments the AD conversion into conditional stages, activating further comparison operations only when the signal requires it. By using a single comparator that operates selectively rather than multiple comparators running continuously, the system achieves high resolution conversion only when needed, significantly reducing average power consumption while maintaining the capability for high-resolution output.
Solution Approach 2:
The patent changes operational parameters dynamically, adjusting the comparison reference signals and conversion depth based on the input signal characteristics. By modifying the reference signal levels and comparison sequence adaptively, a single comparator can achieve variable resolution output, consuming more power only when high resolution is required and less power when lower resolution suffices, thus optimizing the power-resolution tradeoff.
3Area of stationary object
If a single comparator is used with fixed reference signal, then circuit area and power consumption are reduced, but AD conversion accuracy decreases due to comparator variations
Solution Approach 1:
The patent implements feedback mechanisms where the output of each comparison stage informs the next stage's operation. The system uses the comparison results to dynamically adjust subsequent comparison operations, effectively compensating for comparator variations. This feedback-based adaptive comparison ensures that accuracy is maintained through intelligent signal processing rather than through multiple fixed comparators, achieving high precision with a single comparator.
Solution Approach 2:
The patent employs parameter changes in the reference signals and comparison thresholds based on the detected signal characteristics and previous comparison outcomes. By adaptively adjusting comparison parameters, the system compensates for comparator variations and maintains high conversion accuracy. This dynamic parameter adjustment allows a single comparator to achieve the precision that would otherwise require multiple fixed comparators.
4Productivity
If bit-shifting is used to achieve multiple-bit AD conversion with fewer bits, then AD conversion time is reduced, but resolution may be compromised
Solution Approach 1:
The patent segments the bit generation process into multiple comparison stages, where each stage contributes a portion of the final digital output. By using bit-shifting to efficiently combine results from these segmented stages rather than requiring all bits to be generated simultaneously through multiple parallel comparators, the system achieves high conversion speed while maintaining resolution through the sequential accumulation of bit information.
Solution Approach 2:
The patent performs preliminary comparisons to determine signal characteristics before committing to the full conversion process. By using initial comparison results to guide subsequent conversion steps and apply bit-shifting strategies based on predicted signal range, the system optimizes conversion time while ensuring sufficient resolution is achieved through adaptive processing rather than fixed high-bit parallel conversion.
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 enables high-speed readout with reduced AD conversion time and power consumption, while maintaining high resolution, by adaptively selecting the ramp signal slope based on signal amplitude, thus overcoming the limitations of comparator variations and noise.
Implementation Method 1
a pixel for generating a signal by photoelectric conversion
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An imaging apparatus and a method of driving the same that can generate a digital data of a high resolution pixel signal are provided. The imaging apparatus includes: a pixel (10-1) for generating a signal by photoelectric conversion; a comparing circuit (30-1) for comparing a signal based on the pixel with a time-dependent reference signal; a counter circuit (40-1) performing a counting operating until an inversion of a magnitude relation between the signal based on the pixel and the time-dependent reference signal; and a selecting circuit (30-2) for setting a time-dependent change rate of the reference signal, according to a signal level of the signal based on the pixel.