Pixel Biasing Device for Canceling Ramp Ground Noise

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional CMOS image sensors face challenges in canceling ramp ground noise, which causes signal distortion due to differences in ground noise transfer ratios between the ramp signal generation unit and the pixel biasing unit, making it difficult to completely eliminate this noise using existing techniques.

Innovation Solution

A pixel biasing device is introduced that includes a ramp ground noise unit, a bias current generation unit, and a pixel biasing unit, where the ramp ground noise is generated and added to the bias current, allowing for a correlated double sampling (CDS) operation to cancel the ramp ground noise from the ramp signal generator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If different voltages are used in ramp signal generation apparatus and pixel array, then the system can operate with separate power supplies, but pixel power noise, pixel ground noise, and ramp ground noise occur causing signal distortion

Engineering Contradiction:

Improvepower supply flexibilityVSAvoidground noise

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies the 'Blessing in disguise' principle by intentionally adding the harmful ramp ground noise to the bias current in a controlled manner. The noise unit generates the ground noise signal and feeds it back to the bias current generation unit, which then incorporates this noise into the bias current. This converts the harmful noise into a beneficial correction signal that cancels the original ground noise through correlated double sampling in the comparator, thereby eliminating signal distortion while maintaining separate power supplies.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If conventional noise cancellation techniques are applied, then pixel power noise, pixel ground noise, and ramp power noise can be canceled, but ramp ground noise cannot be canceled and signal noise occurs

Engineering Contradiction:

Improvenoise cancellation capabilityVSAvoidsignal accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent implements a feedback mechanism where the ramp ground noise signal is captured from the ramp signal generation apparatus and fed back to the bias current generation unit. This feedback loop allows the system to continuously monitor and adjust the bias current to compensate for ground noise variations, enabling complete cancellation of ramp ground noise while maintaining signal accuracy through the correlated double sampling process.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The bias current acts as an intermediary element that mediates between the ramp signal generation apparatus and the pixel array. By incorporating the ground noise signal into the bias current, the patent creates a noise-cancellation pathway that allows the harmful ground noise to be counteracted before it reaches the pixel signal, thereby improving measurement precision while maintaining reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If ramp ground noise is not canceled, then the system structure remains simple, but signal distortion occurs due to noise

Engineering Contradiction:

Improvesystem structureVSAvoidsignal distortion

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent applies the 'Merging' principle by integrating the noise cancellation functionality into the existing bias current generation pathway. The noise unit and bias current generation unit are merged into a unified system where the ground noise signal is processed and incorporated into the bias current. This merging approach eliminates signal distortion through correlated double sampling while maintaining relatively simple system architecture by utilizing existing circuit components rather than adding entirely separate noise cancellation stages.

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS10051215B2Pixel biasing device for canceling ground noise of ramp signal and image sensor including the same

Publication Date: 2018.08.14 SK HYNIX INC

AI summary

A pixel biasing device includes a ramp ground noise unit, a bias current generation unit, and a pixel biasing unit; the ramp ground noise unit being suitable for generating a ramp ground noise and for transferring the ramp ground noise to the bias current generation unit; the bias current generation unit being suitable for generating a bias current by combining an inputted reference current with the ramp ground noise received from the ramp ground noise unit; and the pixel biasing unit being suitable for performing a biasing operation on an inputted pixel signal based on the bias current.