Pinned Photodiode Charge Transfer for Image Sensor ADC

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Solution Overview

Problem

Conventional signal processing circuitry in imaging systems relies on capacitors for charge transfer, leading to excessive power consumption and limited configurability, which restricts the applicability of image sensors in devices with larger power sources and complicates charge mixing between capacitors.

Innovation Solution

The use of pinned photodiode structures to transfer adjustable size charge packets to circuit nodes, enabling one-directional charge transfer and reducing power consumption by eliminating the need for capacitors in analog-to-digital conversion processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional capacitors are used for charge transfer in ADC circuitry, then charge mixing and reference charge provision are enabled, but power consumption increases and configurability is limited

Engineering Contradiction:

Improveconfigurability of signal processing circuitryVSAvoidpower consumption of capacitor-based circuitry

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent extracts the charge transfer function from conventional capacitors and implements it using pinned photodiode devices. By removing the capacitor component entirely from the charge transfer path, the invention eliminates the power consumption associated with capacitor charging/discharging cycles while maintaining the essential charge transfer capability needed for ADC operation. The pinned photodiode directly transfers charge packets between nodes without requiring intermediate capacitive storage.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention changes the fundamental parameter of charge transfer mechanism from capacitive coupling to photodiode-based charge packet transfer. This parameter change enables configurable charge transfer sizes by controlling the photodiode operation rather than being constrained by fixed capacitor values, thereby improving adaptability while reducing power consumption.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If capacitors are used to transfer large charge packets, then charge transfer capability is achieved, but power dissipation increases

Engineering Contradiction:

Improvecharge transfer capacityVSAvoidpower dissipation in signal processing circuitry

Core Design Contradiction:

Quantity of substanceVSLoss of energy

Solution Approach 1:

The patent replaces the mechanical/electrical capacitor-based charge transfer system with a photodiode-based system that transfers charge through controlled carrier generation and collection. This substitution eliminates the need for repeated charging cycles of large capacitors, thereby reducing power dissipation while maintaining the ability to transfer large charge packets efficiently.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If conventional ADC circuitry with capacitors is used, then reference charge provision is enabled, but device complexity increases

Engineering Contradiction:

Improvesimplicity of signal processing circuitryVSAvoidcomplexity of capacitor-based ADC circuitry

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The pinned photodiode device performs multiple functions: it acts as both the charge transfer element and the reference charge source. By making the photodiode multi-functional, the invention eliminates the need for separate capacitor components and associated control circuitry, thereby reducing device complexity while maintaining ease of manufacture through standardized photodiode fabrication processes.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 allows for lower power consumption and increased configurability in signal processing circuitry, enhancing the performance and efficiency of image sensors by enabling complete charge transfer without the limitations of capacitors, thus improving the applicability of image sensors in various electronic devices.

Implementation Method 1

signal processing circuitry that utilizes pinned photodiode devices for delivering charge to a circuit node

Methodology Applied

Scientific EffectCharge transfer: Photoelectric Effect

Data Source

PatentUS10859434B2Charge packet signal processing using pinned photodiode devices

Publication Date: 2020.12.08 SEMICON COMPONENTS IND LLC

AI summary

An image sensor may include an array of image pixels coupled to analog-to-digital conversion circuitry formed from pinned photodiode charge transfer circuits. Majority charge carriers for the pinned photodiodes in the charge transfer circuits may be electrons for photodiode wells formed from n-type doped regions and may be holes for photodiode formed from p-type doped regions. Pinned photodiodes may be used for charge integration onto a capacitive circuit node. Pinned photodiodes may also be used for charge subtraction from a capacitive circuit node. Comparator circuitry may be used to determine digital values for the pixel output levels in accordance with single-slope conversion, successive-approximation-register conversion, cyclic conversion, and first or second order delta-sigma conversion techniques. The array of image pixels used for imaging may have a conversion mode wherein at least a portion of the pixel circuitry in the array are operated similar to the charge transfer circuits.