Solid State Imaging Device Charge Reset Potential Control

Solution Overview

Problem

Existing solid state imaging devices face challenges in accurately detecting light quantities beyond their saturation level, leading to variations in signal quality and difficulty in capturing images with high dynamic range, especially under high illuminance conditions.

Innovation Solution

A solid state imaging device with a photoelectric conversion unit, charge-voltage conversion unit, charge transfer unit, and charge reset unit, where the driving unit controls the potential of the charge reset unit to accumulate charges up to saturation level, allowing for controlled light exposure and the use of overflow paths formed by depression type transistors to manage charge overflow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the diaphragm or shutter speed is adjusted to the dark portion of a subject, then charges can be accumulated in the photoelectric conversion unit, but the photoelectric conversion unit becomes saturated and cannot properly detect light quantity in bright portions exceeding the saturation level

Engineering Contradiction:

Improvelight quantity detection accuracyVSAvoiddynamic range coverage

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The pixel region is divided into multiple regions with different exposure times. Specifically, a first region has a first exposure time and a second region has a second exposure time that is longer than the first exposure time. This segmentation allows different parts of the image to be exposed for different durations, enabling simultaneous capture of both bright and dark areas without saturation in bright regions while ensuring sufficient charge accumulation in dark regions.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If the diaphragm or shutter speed is adjusted to the bright portion of the subject, then saturation of the photoelectric conversion unit is avoided, but charges are not sufficiently accumulated in dark portions leading to degraded image quality and insufficient signal to noise ratio

Engineering Contradiction:

Improvedynamic range coverageVSAvoidlight quantity detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The pixel region is divided into multiple regions with different exposure times. Specifically, a first region has a first exposure time and a second region has a second exposure time that is longer than the first exposure time. This segmentation allows different parts of the image to be exposed for different durations, enabling simultaneous capture of both bright and dark areas without saturation in bright regions while ensuring sufficient charge accumulation in dark regions.

Inventive Principle:

Principle #1Segmentation

3Adaptability or versatility

If multiple images with different exposure times are captured and combined to increase dynamic range, then both bright and dark portions can be properly detected, but a frame memory is necessary which increases device size and cost

Engineering Contradiction:

Improvedynamic rangeVSAvoiddevice size

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The pixel region is divided into multiple regions with different exposure times. Specifically, a first region has a first exposure time and a second region has a second exposure time that is longer than the first exposure time. This segmentation allows different parts of the image to be exposed for different durations, enabling simultaneous capture of both bright and dark areas without saturation in bright regions while ensuring sufficient charge accumulation in dark regions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The signals from regions with different exposure times are combined through signal processing to generate a single image with extended dynamic range. This merging process integrates the advantages of both short and long exposure regions, allowing the device to capture both bright and dark areas in a single shot without requiring separate frame memory storage for multiple images.

Inventive Principle:

Principle #5Merging (Combining)

4Device complexity

If a single signal is generated using two pixels with different exposure times, then a memory is unnecessary, but the resolution deteriorates

Engineering Contradiction:

Improvememory requirementVSAvoidresolution

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The pixel region is divided into multiple regions with different exposure times. Specifically, a first region has a first exposure time and a second region has a second exposure time that is longer than the first exposure time. This segmentation allows different parts of the image to be exposed for different durations, enabling simultaneous capture of both bright and dark areas without saturation in bright regions while ensuring sufficient charge accumulation in dark regions.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of combining signals horizontally from neighboring pixels, the patent extends the approach vertically across multiple pixel rows. Multiple rows are assigned different exposure times, creating a vertical dimension of exposure time variation. This approach maintains vertical resolution while achieving extended dynamic range, as the combination occurs along the row dimension rather than reducing pixel count.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 effectively suppresses signal variations at high illuminance levels, enabling the capture of images with appropriate dynamic range by converting the signal to logarithmic form and maintaining image quality across varying light conditions.

Implementation Method 1

a photoelectric conversion unit that performs photoelectric conversion of converting incident light into charges and accumulates the charges

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS9143712B2Solid state imaging device, driving method of solid state imaging device, and electronic device having a driving unit so that a potential of a drain of a charge reset unit is controlled

Publication Date: 2015.09.22 SONY SEMICON SOLUTIONS CORP

AI summary

There is provided a solid state imaging device including a photoelectric conversion unit that performs photoelectric conversion of converting incident light into charges and accumulates the charges, a charge-voltage conversion unit that converts the charges which have been subjected to the photoelectric conversion by the photoelectric conversion unit into a voltage, a charge transfer unit that transfers charges to the charge-voltage conversion unit, a charge reset unit that resets charges of the charge-voltage conversion unit, and a driving unit that performs driving such that a potential of a drain of the charge reset unit is controlled so that the charges are accumulated in the photoelectric conversion unit and the charge-voltage conversion unit up to a saturation level, and then the photoelectric conversion unit is subject to light exposure.