Continuous-Time Sigma-Delta ADC Low-Pass Feedback for Lower Op-Amp Bandwidth

Solution Overview

Problem

Conventional continuous time sigma-delta analog-to-digital converters require operational amplifiers with high bandwidth and high slew rate to suppress distortion and maintain a high signal-to-noise ratio, leading to high power dissipation and performance demands.

Innovation Solution

The design incorporates a feed-forward integrator path with a feedback digital-to-analog converter and a low pass filter, which reduces the bandwidth and slew rate requirements of the operational amplifier by filtering high-frequency components before they reach the amplifier, using a feedback resistor and capacitor configuration to achieve loop stability and noise suppression.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If operational amplifiers with high bandwidth and high slew rate are used, then signal-to-noise ratio is improved and distortion is suppressed, but power dissipation increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidpower dissipation

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The feedback path is segmented into two separate paths: a feed-forward path that handles high-frequency signal components and a feedback path that handles low-frequency components. This segmentation allows the operational amplifier to operate with relaxed bandwidth requirements while maintaining high signal-to-noise ratio, thereby reducing power dissipation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A feedback low-pass filter is introduced as an intermediary component in the feedback path. This filter separates high-frequency components (handled by the feed-forward path) from low-frequency components (handled by the feedback path), allowing the operational amplifier to operate at lower bandwidth and slew rate while maintaining performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If operational amplifiers with high bandwidth are used, then distortion of feedback signal is suppressed, but device complexity increases

Engineering Contradiction:

Improvedistortion suppressionVSAvoidoperational amplifier specifications

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The feedback path is segmented into two separate paths: a feed-forward path that handles high-frequency signal components and a feedback path that handles low-frequency components. This segmentation allows the operational amplifier to operate with relaxed bandwidth requirements while maintaining high signal-to-noise ratio, thereby reducing power dissipation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A feedback low-pass filter is introduced as an intermediary component in the feedback path. This filter separates high-frequency components (handled by the feed-forward path) from low-frequency components (handled by the feedback path), allowing the operational amplifier to operate at lower bandwidth and slew rate while maintaining performance.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 configuration allows for the use of operational amplifiers with relaxed performance specifications, reducing power dissipation while maintaining a high signal-to-noise ratio and minimizing distortion, thereby improving the efficiency of the analog-to-digital conversion process.

Implementation Method 1

a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summator

Methodology Applied

Scientific EffectLow pass filtering: Filter (electronic)

Implementation Method 2

A low unit gain bandwidth or low slew rate of the operational amplifier employed by the integrator gives rise to distortion of the feedback signal

Methodology Applied

Scientific EffectOperational amplification:

Implementation Method 3

using a feedback resistor and capacitor configuration to achieve loop stability and noise suppression

Methodology Applied

Scientific EffectRC filtering: Filter (electronic)

Data Source

PatentUS8749416B2Continuous time sigma-delta A/D converter and electrical system comprising the A/D converter

Publication Date: 2014.06.10 STMICROELECTRONICS INT NV

AI summary

A continuous time sigma-delta analog-to-digital converter comprising: a summator of an input analog signal and a feedback signal; a feed-forward integrator path connected to the summator and configured to provide a digital signal; a feedback digital-to-analog converter to convert the digital signal into a feedback analog signal; a feedback low pass filter structured to filter the feedback analog signal and provide the feedback signal to the summator.