CMOS Image Sensor AD Conversion With Adaptive Reference Ramp

Solution Overview

Problem

Digital cameras using CMOS image sensors face challenges in achieving high-speed readout and high resolution due to variations in comparator manufacturing elements, leading to errors in analog-to-digital (AD)-converted data, and difficulties in increasing circuit area and power consumption.

Innovation Solution

The imaging apparatus incorporates a pixel for photoelectric conversion, a comparing circuit that compares the pixel 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

VSEngineering Contradiction Analysis

1Measurement precision

If multiple comparators are used for AD conversion, then measurement precision is improved, but device complexity and power consumption increase

Engineering Contradiction:

ImproveAD conversion precisionVSAvoidcircuit area

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the AD conversion process into multiple stages: a first comparator performs initial conversion with a first reference signal, and a second comparator performs subsequent conversion with a second reference signal. This segmentation allows high-precision conversion to be achieved through sequential processing rather than parallel multiple-comparator operation, reducing circuit area while maintaining measurement precision.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first comparator performs preliminary AD conversion to generate intermediate digital data before the second comparator performs the final conversion. This preliminary action reduces the dynamic range that the second comparator must handle, enabling the use of a simpler second comparator circuit while still achieving high overall precision.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If multiple comparators are used for AD conversion, then measurement precision is improved, but power consumption increases

Engineering Contradiction:

ImproveAD conversion precisionVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent segments the AD conversion process into multiple stages: a first comparator performs initial conversion with a first reference signal, and a second comparator performs subsequent conversion with a second reference signal. This segmentation allows high-precision conversion to be achieved through sequential processing rather than parallel multiple-comparator operation, reducing circuit area while maintaining measurement precision.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first comparator performs preliminary AD conversion to generate intermediate digital data before the second comparator performs the final conversion. This preliminary action reduces the dynamic range that the second comparator must handle, enabling the use of a simpler second comparator circuit while still achieving high overall precision.

Inventive Principle:

Principle #10Preliminary action

3Measurement precision

If more bits are used for signal classification, then measurement precision is improved, but productivity decreases

Engineering Contradiction:

Improvesignal resolutionVSAvoidreadout speed

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The first comparator performs preliminary AD conversion to generate intermediate digital data before the second comparator performs the final conversion. This preliminary action reduces the dynamic range that the second comparator must handle, enabling the use of a simpler second comparator circuit while still achieving high overall precision.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent dynamically adjusts the reference signals used in the conversion process. The first comparator uses a first reference signal for initial conversion, and the second comparator uses a second reference signal for final conversion. This dynamic adaptation allows the system to achieve high precision without requiring excessive bits throughout the entire conversion chain, thereby maintaining readout speed.

Inventive Principle:

Principle #15Dynamics

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

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS9912894B2Imaging apparatus and method of driving the same

Publication Date: 2018.03.06 CANON KK

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.