NS SAR ADC Kickback Noise Cancellation With Cross-Coupled Capacitors

Solution Overview

Problem

Kickback noise caused by comparator equalization in successive-approximation register (SAR) analog-to-digital converters (ADCs) affects the accuracy of upstream circuitry, particularly in low-power environments, and conventional solutions like bulky decoupling capacitors or high-powered amplifiers are impractical.

Innovation Solution

Implementing a set of cross-coupled capacitive elements between the comparator and the noise shaping (NS) filter to cancel voltage swings, using capacitors or transistors with matched capacitance properties to neutralize opposite-polarity kickback noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional decoupling capacitors or high-powered amplifiers are used to reduce kickback noise, then kickback noise is reduced, but chip size and power consumption increase

Engineering Contradiction:

Improvekickback noiseVSAvoidpower consumption

Core Design Contradiction:

Object-affected harmful factorsVSUse of energy by moving object

Solution Approach 1:

The patent converts the harmful kickback noise generated by comparator equalization into a beneficial effect by using cross-coupled capacitive elements to generate an opposing voltage swing that cancels the kickback noise. The harmful voltage swing from equalization is transformed into a useful cancellation mechanism that reduces noise without requiring additional power-consuming components.

Inventive Principle:

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

Solution Approach 2:

The cross-coupled capacitive elements act as intermediary components between the comparator and the noise shaping filter. These capacitors store and transfer charge to generate the canceling voltage swing, mediating the interaction between the comparator's equalization function and the filter's noise reduction function without requiring bulky decoupling capacitors or high-powered amplifiers.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If conventional decoupling capacitors or high-powered amplifiers are used to reduce kickback noise, then kickback noise is reduced, but chip size increases

Engineering Contradiction:

Improvekickback noiseVSAvoidchip size

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

The patent converts the harmful kickback noise generated by comparator equalization into a beneficial effect by using cross-coupled capacitive elements to generate an opposing voltage swing that cancels the kickback noise. The harmful voltage swing from equalization is transformed into a useful cancellation mechanism that reduces noise without requiring bulky decoupling capacitors or high-powered amplifiers.

Inventive Principle:

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

Solution Approach 2:

The cross-coupled capacitive elements act as intermediary components between the comparator and the noise shaping filter. These capacitors store and transfer charge to generate the canceling voltage swing, mediating the interaction between the comparator's equalization function and the filter's noise reduction function without requiring bulky decoupling capacitors or high-powered amplifiers.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If comparator equalization is performed to improve ADC accuracy, then measurement precision is improved, but kickback noise is generated

Engineering Contradiction:

ImproveADC accuracyVSAvoidkickback noise

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary anti-action by generating a canceling voltage swing through the cross-coupled capacitive elements before the kickback noise can adversely affect the ADC accuracy. The capacitors are pre-charged during the equalization process and then discharge to produce the opposing voltage swing that neutralizes the kickback noise, allowing comparator equalization to proceed without generating harmful effects.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The patent converts the harmful kickback noise generated by comparator equalization into a beneficial effect by using cross-coupled capacitive elements to generate an opposing voltage swing that cancels the kickback noise. The harmful voltage swing from equalization is transformed into a useful cancellation mechanism that reduces noise without requiring additional power-consuming components.

Inventive Principle:

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

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

Effectively reduces or cancels kickback noise without increasing chip size or power consumption, maintaining ADC accuracy and suitability for low-power applications.

Implementation Method 1

a set of capacitive elements cross-coupled to the differential input path. The set of capacitive elements may include a first capacitor coupled between a first input line of the pair of differential input paths and a second input line of the pair of differential input paths

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS12476648B2Noise shaping successive-approximation register (SAR) analog-to-digital converter (ADC)

Publication Date: 2025.11.18 INFINEON TECHNOLOGIES AMERICAS CORP

AI summary

A noise-shaping successive-approximation register (SAR) analog-to-digital converter (ADC) (SAR ADC) including a noise-shaping (NS) filter, a comparator, a differential input path between the NS filter and the comparator, and a cross-coupled set of capacitive elements coupled to the differential input path.