ADC Reference Signal Slope Control for Image Sensor Conversion
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Solution Overview
Problem
Existing image capturing apparatuses with analog-to-digital converters face issues of signal gaps and noise differences due to varying conversion gains and reference signal slopes, leading to inaccuracies in digital signal conversion, especially near threshold values for luminance judgment.
Innovation Solution
An analog-to-digital converter system comprising a generator that produces a reference signal with a constant slope initially and a steeper slope later, a comparator for voltage comparison, and a counter to manage the conversion process, ensuring consistent and high-speed conversion without signal gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two types of reference signals with different slopes are used to speed up AD conversion, then conversion speed is improved, but signal gaps and noise differences occur due to conversion gain variations and wiring layout differences
Solution Approach 1:
The patent changes the voltage slope parameter of the reference signal dynamically based on the input signal level. A first reference signal with a first voltage slope is used for low-luminance signals, while a second reference signal with a second voltage slope is used for high-luminance signals. This parameter change approach allows optimization of conversion speed for different signal conditions while maintaining accuracy through correlated double sampling that eliminates the impact of conversion gain variations.
Solution Approach 2:
The patent implements a feedback mechanism where the determination of which reference signal to use is based on the pixel output voltage level. The system continuously monitors the input signal and selects the appropriate reference signal slope, creating a closed-loop control that adapts to different luminance conditions and maintains measurement precision across the full dynamic range.
2Loss of time
If a steeper slope reference signal is used, then conversion time is reduced, but conversion noise increases relative to the pixel output voltage
Solution Approach 1:
The patent dynamically changes the reference signal voltage slope parameter based on the input signal amplitude. For low-luminance pixel output voltages, a gentler slope is used to minimize conversion noise relative to the small signal amplitude. For high-luminance signals, a steeper slope is used to reduce conversion time since the larger signal amplitude can tolerate higher noise levels. This conditional parameter change optimizes both speed and noise performance across different operating conditions.
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 solution enables high-speed analog-to-digital conversion while minimizing signal and noise gaps, maintaining a proportional relationship between light intensity and digital signal magnitude, and reducing readout noise variability.
Implementation Method 1
Each of the plurality of pixels includes a photoelectric converter that generates an electric signal corresponding to an amount of incident light
Data Source
AI summary
An analog-to-digital converter includes a generator, a comparator, and a counter. The generator generates a reference signal whose voltage changes with respect to time. The voltage of the reference signal changes with a constant slope in a predetermined first period since the voltage starts changing. The slope of the voltage becomes steeper with respect to time in a second period after the first period. The comparator compares the reference signal and a voltage output from outside, and outputs a comparison result. The counter counts at a predetermined first cycle since the voltage of the reference signal starts changing until the comparison result is inverted.