Adjustable Ground Level Boosting for BJT Pixel Storage Capacitors

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional optical tracking systems using pixel circuits with photo detectors suffer from degraded image contrast and performance due to voltage saturation of storage capacitors in high light intensity environments, leading to poor image quality.

Innovation Solution

A bipolar junction transistor (BJT) pixel circuit with a photo detector, shutter circuit, and storage capacitor, where the adjustable ground level is boosted to prevent voltage saturation, allowing for dynamic adjustment of the storage capacitor's voltage during exposure to maintain image data quality.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If the storage capacitor is discharged in high light intensity environment, then the photo detector can capture light energy, but the voltage of storage capacitor becomes saturated leading to degraded image contrast

Engineering Contradiction:

Improvelight intensityVSAvoidimage contrast

Core Design Contradiction:

Illumination intensityVSMeasurement precision

Solution Approach 1:

The patent applies parameter changes by dynamically adjusting the ground level voltage (VGL) of the storage capacitor during the exposure period. When high light intensity causes the storage capacitor voltage to approach saturation, the controlling circuit detects this condition and raises VGL, thereby resetting the voltage difference across the capacitor and preventing saturation. This dynamic parameter adjustment allows the pixel circuit to maintain optimal voltage range for accurate image data storage under varying light conditions.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the storage capacitor voltage is kept high to avoid saturation, then image contrast is maintained, but the dynamic range for capturing light intensity variations is reduced

Engineering Contradiction:

Improveimage contrastVSAvoiddynamic range

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent implements dynamics by making the ground level voltage VGL adjustable and controllable during the exposure period. Instead of using a fixed ground level, the controlling circuit dynamically changes VGL based on the detected voltage level of the storage capacitor and the current light intensity conditions. This dynamic adjustment allows the system to adapt to different lighting scenarios, maintaining both image contrast and dynamic range by optimizing the voltage range utilization in real-time.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If conventional pixel circuits are used without adjustable ground level, then the circuit structure is simple, but voltage saturation occurs in high light intensity conditions

Engineering Contradiction:

Improvecircuit structureVSAvoidvoltage saturation prevention

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent introduces an intermediary component - the controlling circuit - that mediates between the photo detector and the storage capacitor. This controlling circuit includes a voltage detection unit that monitors the storage capacitor voltage and a ground level adjustment unit that modifies VGL accordingly. This intermediary layer adds complexity but provides intelligent control to prevent voltage saturation, thereby improving reliability without requiring fundamental changes to the basic pixel circuit architecture.

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

Significantly improves image contrast and tracking performance by preventing voltage saturation, even in high light intensity conditions, resulting in better image quality for optical tracking systems.

Implementation Method 1

The photo detector has a first end coupled to the base of the BJT transistor and a second end coupled to the reference ground level, and it is used for generating a base current based on a light intensity of a light incident on the photo detector

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS11282888B1Scheme of boosting adjustable ground level(s) of storage capacitor(s) of BJT pixel circuit(s) in pixel array circuit of image sensor apparatus

Publication Date: 2022.03.22 PIXART IMAGING INC

AI summary

A bipolar junction transistor (BJT) pixel circuit, including: a BJT transistor, having a base coupled to a photo detector, an emitter coupled to a shutter circuit, and a collector coupled to a reference ground level; the photo detector, having first end coupled to the base of BJT transistor and second end coupled to the reference ground level, for generating base current based on light intensity of light incident on the photo detector; the shutter circuit, coupled to the emitter of the BJT transistor, for controlling exposure time of the photo detector according to a shutter signal; and a storage capacitor, coupled between the shutter circuit and an adjustable ground level different from the reference ground level, for storing image data captured by the photo detector, wherein the adjustable ground level is boosted to be higher than the reference ground level for one or more times during the exposure time.