Image Sensor Pixel Charge Control for Optical Navigation Overexposure

Solution Overview

Problem

Conventional optical navigating apparatuses face accuracy issues due to overexposure from bright environment light, which affects the capture of frames with only light source light, leading to inaccuracy in determining object location.

Innovation Solution

An image sensing apparatus with a sensing pixel structure that includes a charge storing device, a light sensing device generating different amounts of photoelectrons in two modes, and a switch device controlled by a control voltage to manage charge transmission, ensuring that the charge amounts are within the device's capacity, thereby avoiding overexposure and optimizing signal-to-noise ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the charge storing device stores all photoelectrons generated by environment light and light source light, then the light sensing device can capture complete light information, but the charge storing device exceeds its maximum charge storing amount causing overexposure

Engineering Contradiction:

Improveaccuracy for determining object locationVSAvoidoverexposure from environment light

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent segments the photoelectron storage process into two distinct phases: first storing photoelectrons generated during the light source off-period, then storing additional photoelectrons generated during the light source on-period. This segmentation allows the system to handle environment light and light source light separately, preventing overexposure while maintaining measurement accuracy.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent performs preliminary action by first capturing the environment light component (when light source is off) before capturing the combined environment light and light source light (when light source is on). This preliminary capture of environment light allows the system to subtract it later, isolating the light source contribution without exceeding charge storage capacity.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If the charge storing device increases its capacity to store all photoelectrons, then overexposure is avoided, but the device complexity and charge storing device size increase

Engineering Contradiction:

Improveavoidance of overexposureVSAvoidcharge storing device capacity requirements

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent performs preliminary action by first capturing the environment light component (when light source is off) before capturing the combined environment light and light source light (when light source is on). This preliminary capture of environment light allows the system to subtract it later, isolating the light source contribution without exceeding charge storage capacity.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent uses periodic action by alternating between two measurement periods: one period with the light source off to capture environment light, and another period with the light source on to capture combined light. This periodic switching allows the system to separate and process different light components sequentially, avoiding the need for large charge storage capacity.

Inventive Principle:

Principle #19Periodic action

3Measurement precision

If the system captures frames during both light source on and off periods, then the light source light can be isolated through subtraction, but the processing time and complexity increase

Engineering Contradiction:

Improveaccuracy for isolating light source lightVSAvoidtime for capturing and processing multiple frames

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent uses periodic action by alternating between two measurement periods: one period with the light source off to capture environment light, and another period with the light source on to capture combined light. This periodic switching allows the system to separate and process different light components sequentially, avoiding the need for large charge storage capacity.

Inventive Principle:

Principle #19Periodic action

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 solution effectively prevents overexposure and enhances the signal-to-noise ratio by ensuring that the charge amounts are within the device's capacity, improving the accuracy of frame acquisition and object location determination.

Implementation Method 1

a light sensing device PD (ex. a photo diode) and generates charges according to received light

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS9244541B2Image sensing apparatus and optical navigating apparatus with the image sensing apparatus

Publication Date: 2016.01.26 PIXART IMAGING INC

AI summary

An image sensing apparatus comprises at least one sensing pixel and a control circuit. The sensing pixel comprises: a charge storing device; a light sensing device, for respectively generating photoelectrons with a first, second amount in a first, second mode; and a switch device, for determining an amount that the photoelectron can be transmitted to the charge storing device according to a control voltage. The control voltage generates the control voltage to control the amount that the photoelectrons can be transmitted to the charge storing device to be a first charge amount in a first mode and to be a second charge amount in a second mode. The first, second charge amounts are smaller than a maximum charge storing amount for the charge storing device.