Current Steering Architecture for High Supply Noise Rejection

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Solution Overview

Problem

Conventional CMOS image sensors face challenges in achieving high power supply noise rejection and maintaining linearity while operating within strict power efficiency and noise constraints, particularly due to noise contributions from ramp voltage generators and comparators, which can result in image blurring and distortions.

Innovation Solution

A current steering architecture is implemented, utilizing a sample and hold block and a driver to control a current steering network, generating signals that track supply voltage variations to produce a ramp voltage with high power supply noise rejection, even at low ramp voltages, while maintaining high linearity over the entire ramp voltage range.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional ramp voltage generators are used, then device complexity is reduced, but power supply noise rejection deteriorates

Engineering Contradiction:

Improvepower supply noise rejectionVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The ramp voltage generator is divided into multiple independent current sources, each generating a specific portion of the ramp voltage. This segmentation allows each current source to be independently optimized for noise rejection while maintaining overall system functionality, resolving the contradiction between improved PSR and increased complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Supply tracking is implemented preliminarily by generating tracking signals before the ramp voltage generation process begins. These tracking signals are prepared in advance to compensate for power supply variations, enabling high noise rejection without requiring complex real-time correction mechanisms.

Inventive Principle:

Principle #10Preliminary action

2Object-affected harmful factors

If ramp voltage is increased to improve signal level, then image tolerance to ramp noise increases, but power consumption increases

Engineering Contradiction:

Improveimage tolerance to ramp noiseVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts the ramp voltage level based on actual noise conditions and signal requirements. By making the ramp voltage adaptive rather than fixed, the system can operate at lower power levels when high tolerance is sufficient, while only increasing voltage when absolutely necessary, thus resolving the power consumption contradiction.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the approach from increasing voltage amplitude to improving voltage stability through supply tracking. By modifying the tracking parameter to follow supply voltage variations, the system achieves better noise tolerance without necessarily increasing power consumption, as the focus shifts from amplitude to stability.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If multiple current sources are used to improve PSR, then power supply noise rejection improves, but device complexity increases

Engineering Contradiction:

Improvepower supply noise rejectionVSAvoiddevice complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

Each current source in the multi-source architecture is designed to perform multiple functions: generating its portion of the ramp voltage, providing supply tracking independently, and contributing to overall noise rejection. This multi-functionality reduces the need for separate dedicated components, thereby limiting the increase in device complexity while maintaining improved PSR.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Object-affected harmful factors

If supply tracking is implemented at all ramp voltage levels, then PSR is maximized, but linearity deteriorates at higher ramp voltages

Engineering Contradiction:

Improvepower supply noise rejectionVSAvoidlinearity

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The system applies different quality characteristics to different portions of the ramp voltage. Supply tracking is applied with appropriate gain and attenuation at each stage, allowing optimal PSR at each local region of the ramp voltage range. This local optimization prevents the degradation of linearity that would result from uniform supply tracking across the entire voltage range.

Inventive Principle:

Principle #3Local quality

Data Source

PatentUS11363228B1Current steering architecture with high supply noise rejection

Publication Date: 2022.06.14 SHENZHEN GOODIX TECH CO LTD

AI summary

Techniques are described for implementing ramp voltage generators with current steering architectures that provide high power supply noise rejection. For example, a current steering architecture uses a sample and hold block and a driver block to control and drive a current steering network. Both generate signals that track supply voltage variations, and those signals are used to generate a ramp voltage. For image sensor applications, image tolerance to ramp noise can be very low when the ramp voltage is low, but can increase appreciably as the ramp voltage increases. As such, embodiments can be implemented to provide high PSR at low ramp voltages, even if the PSR degrades at higher ramp voltages, while maintaining high linearity over the entire ramp voltage.