Pixel Signal Holding Circuit for Charge Injection Error Reduction

Solution Overview

Problem

The existing photoelectric conversion devices have limitations in improving the accuracy of output signals, particularly in solid-state imaging elements with sample-and-hold circuits, where signal holding and amplification processes can introduce errors.

Innovation Solution

A photoelectric conversion device is designed with a pixel configuration that includes a signal line connected to a first signal holding unit comprising a first and second capacitor element, an amplifier circuit, and switches, allowing for improved signal holding and amplification through correlated double sampling and delta-sigma analog-to-digital conversion, reducing relative error in gain components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional sample-and-hold circuit is used to hold signals from pixels, then the circuit structure is simple, but the output signal accuracy is insufficient due to relative gain errors from charge injection

Engineering Contradiction:

Improveoutput signal accuracyVSAvoidcircuit structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The pixel array is divided into multiple regions (first region and second region) with different photoelectric conversion units, allowing differential measurement to eliminate common-mode errors including charge injection effects. This segmentation enables accurate signal holding without requiring complex compensation circuits in each pixel.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dedicated sample-and-hold circuit is introduced as an intermediary component between the pixel array and readout circuitry. This separate holding circuit with capacitor and switch isolates the pixel signal path from the readout path, preventing charge injection errors from affecting signal accuracy while maintaining overall circuit simplicity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If multiple signal lines are connected to a single sample-and-hold circuit, then device complexity is reduced, but signal accuracy deteriorates due to charge injection errors

Engineering Contradiction:

Improvenumber of sample-and-hold circuitsVSAvoidsignal holding accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The pixel array is divided into multiple regions (first region and second region) with different photoelectric conversion units, allowing differential measurement to eliminate common-mode errors including charge injection effects. This segmentation enables accurate signal holding without requiring complex compensation circuits in each pixel.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The circuit uses correlated double sampling with feedback mechanisms where the sample-and-hold circuit stores reference signals and signal signals, and the readout circuit processes the difference between them. This feedback approach cancels out charge injection errors that occur during switching operations.

Inventive Principle:

Principle #23Feedback

3Ease of manufacture

If a simple holding circuit is used, then manufacturing is easier, but relative gain errors from charge injection reduce signal accuracy

Engineering Contradiction:

Improvecircuit fabrication simplicityVSAvoidoutput signal accuracy

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The pixel array is divided into multiple regions (first region and second region) with different photoelectric conversion units, allowing differential measurement to eliminate common-mode errors including charge injection effects. This segmentation enables accurate signal holding without requiring complex compensation circuits in each pixel.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A dedicated sample-and-hold circuit is introduced as an intermediary component between the pixel array and readout circuitry. This separate holding circuit with capacitor and switch isolates the pixel signal path from the readout path, preventing charge injection errors from affecting signal accuracy while maintaining overall circuit simplicity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The proposed solution enhances the accuracy of output signals by reducing relative errors in gain components, enabling high dynamic range imaging and improved image quality.

Implementation Method 1

a photoelectric conversion unit configured to convert incident light into a signal

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS20230282654A1Photoelectric conversion device

Publication Date: 2023.09.07 CANON KK

AI summary

A photoelectric conversion device includes a pixel, a signal line connected to the pixel, and a first signal holding unit to which a signal is input from the pixel via the signal line. The first signal holding unit includes a first capacitor element and a second capacitor element each configured to hold a signal input from the signal line to a first terminal, an amplifier circuit in which a second terminal of the first capacitor element and a second terminal of the second capacitor element is connected to an input terminal, a first switch connected between the first terminal of the first capacitor element and an output terminal of the amplifier circuit, a second switch connected between the first terminal of the second capacitor element and the output terminal of the amplifier circuit, and a third switch connected to the input terminal of the amplifier circuit.