CMOS Image Sensor AD Conversion With Adaptive Reference Slope
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Solution Overview
Problem
Digital cameras using 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 includes a pixel for generating a signal through photoelectric conversion, a comparing circuit for comparing the signal with a time-dependent reference signal, a counter circuit for counting until the magnitude relation inversion, and a selecting circuit that sets the time-dependent change rate of the reference signal based on the signal level, allowing for efficient AD conversion with reduced bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple comparators are used for AD conversion, then measurement precision is improved, but device complexity 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 amplitude ranges. The signal is first classified into coarse ranges, then progressively refined through multiple conversion stages, achieving high precision without requiring multiple comparators to operate simultaneously.
Solution Approach 2:
The patent dynamically adjusts the reference signal characteristics (slope, range) based on the input signal amplitude detected in previous stages. This dynamic adaptation allows a single comparator to effectively handle different signal ranges with optimal precision, replacing the need for multiple fixed comparators.
2Measurement precision
If multiple comparators are used for AD conversion, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent segments the AD conversion into multiple sequential stages using a single comparator, eliminating the need for multiple comparators to operate simultaneously. This reduces power consumption while maintaining precision through progressive refinement of the digital output across stages.
Solution Approach 2:
The patent employs periodic, sequential operation of the single comparator across multiple conversion stages rather than continuous operation of multiple comparators. The comparator is activated in sequence for different signal ranges and stages, reducing overall power consumption while achieving the required measurement precision.
3Productivity
If the number of bits is reduced for high-speed readout, then productivity is improved, but measurement precision deteriorates
Solution Approach 1:
The patent segments the precision requirements into multiple conversion stages, where each stage contributes a portion of the final digital bits. This allows the system to achieve high overall precision through sequential stages rather than requiring all bits to be resolved simultaneously, enabling high-speed readout without sacrificing final measurement precision.
Solution Approach 2:
The patent performs preliminary classification of the input signal into coarse amplitude ranges before the main AD conversion. This preliminary action reduces the dynamic range that the main converter must handle, allowing for faster conversion speed while maintaining overall precision through the combination of preliminary classification results and subsequent fine 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 and high-resolution AD conversion by reducing the number of bits required, minimizing errors, and optimizing circuit area and power consumption, while maintaining sufficient signal-to-noise ratio.
Implementation Method 1
a pixel for generating a signal by photoelectric conversion
Data Source
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.