Sampled Bandgap Reference for CMOS Image Sensors

Solution Overview

Problem

Conventional CMOS image sensors face challenges in maintaining stable reference levels for analog-to-digital conversion, which can lead to photon emissions that impact the operation of photosensitive elements, particularly in portable devices where power efficiency and noise constraints are stringent.

Innovation Solution

A sampled bandgap reference generator is integrated with the CMOS image sensor, operating in cycles with an active core that dynamically stabilizes the reference level and then deactivates to minimize photon emissions, using a sample and hold mechanism to provide a stable reference during the inactive phase.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a conventional continuously operating bandgap reference generator is used to provide stable reference levels for ADC conversion, then reference level stability is improved, but photon emissions increase that adversely impact the photosensitive elements of the image sensor

Engineering Contradiction:

Improvereference level stabilityVSAvoidphoton emissions

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The bandgap reference generator operates in periodic cycles, alternating between an active phase where the reference level is dynamically stabilized and a sleep phase where the core is deactivated. This periodic operation maintains reference stability when needed while minimizing photon emissions during the sleep phase, directly resolving the contradiction between stability and harmful emissions.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system dynamically switches between two operational states: active and sleep. The controller adjusts the operational phase of the bandgap reference generator based on timing signals, enabling the system to adapt its behavior to balance reference stability requirements against photon emission constraints, thereby resolving the contradiction through dynamic state management.

Inventive Principle:

Principle #15Dynamics

2Stability of the object's composition

If the bandgap core is continuously activated to maintain dynamically stabilized reference levels, then reference level stability is improved, but power consumption increases

Engineering Contradiction:

Improvereference level stabilityVSAvoidpower consumption

Core Design Contradiction:

Stability of the object's compositionVSUse of energy by moving object

Solution Approach 1:

The bandgap reference generator operates in periodic cycles, alternating between an active phase where the reference level is dynamically stabilized and a sleep phase where the core is deactivated. This periodic operation maintains reference stability when needed while minimizing photon emissions during the sleep phase, directly resolving the contradiction between stability and harmful emissions.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system dynamically switches between two operational states: active and sleep. The controller adjusts the operational phase of the bandgap reference generator based on timing signals, enabling the system to adapt its behavior to balance reference stability requirements against power consumption constraints, thereby resolving the contradiction through dynamic state management.

Inventive Principle:

Principle #15Dynamics

3Stability of the object's composition

If the bandgap core is continuously activated to provide stable reference levels, then reference level stability is improved, but noise increases that impacts image sensor performance

Engineering Contradiction:

Improvereference level stabilityVSAvoidnoise

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

The bandgap reference generator operates in periodic cycles, alternating between an active phase where the reference level is dynamically stabilized and a sleep phase where the core is deactivated. This periodic operation maintains reference stability when needed while minimizing photon emissions during the sleep phase, directly resolving the contradiction between stability and harmful emissions.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system dynamically switches between two operational states: active and sleep. The controller adjusts the operational phase of the bandgap reference generator based on timing signals, enabling the system to adapt its behavior to balance reference stability requirements against noise constraints, thereby resolving the contradiction through dynamic state management.

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS11470272B1CMOS image sensing with sampled bandgap reference

Publication Date: 2022.10.11 SHENZHEN GOODIX TECH CO LTD

AI summary

Techniques are described for sampled bandgap reference generation for CMOS image sensor (CIS) applications. For example, the CIS includes a pixel array, one or more pixel analog to digital converters (ADCs), and a sampled bandgap reference generator, all integrated in close proximity on a chip. The ADCs rely on stable reference levels from the bandgap reference generator for performing pixel conversions for the pixel array. Embodiments of the sampled bandgap reference generator can operate according to reference generation cycles. Each cycle can include a first portion, in which an active core dynamically stabilizes the bandgap reference level; and a second portion, in which the core is deactivated, and the bandgap reference level is output based on a sampled level obtained during the preceding first portion of the cycle. The cycle timing can be controlled to achieve sufficient dynamic stabilization of the reference levels, while mitigating photon emissions from the core.