Dual-Input ADC Circuit With Anti-Aliasing and Precise DC Sensing

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Solution Overview

Problem

Existing ADC architectures face challenges in combining high bandwidth with good AC performance and high DC precision, with resistive input ADCs struggling to achieve good DC performance due to voltage coefficients, flicker noise, and instability, while capacitive input ADCs are difficult to drive and prone to aliasing.

Innovation Solution

A wide bandwidth ADC circuit is developed by combining a resistive-input continuous-time sigma-delta ADC circuit with a second ADC circuit having a switched capacitor input, allowing for easy driving, alias-free operation, and excellent DC precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a resistive-input ADC circuit is used, then the ADC is easy to drive and provides wide bandwidth operation, but DC precision deteriorates due to voltage coefficients, flicker noise, and instability

Engineering Contradiction:

Improveease to driveVSAvoidDC precision

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The ADC system is divided into two independent ADC circuits: a first ADC circuit with resistive input for wide bandwidth AC signals, and a second ADC circuit with switched capacitor input for DC and low-frequency signals. Each circuit is optimized for its specific function, allowing the system to achieve both ease of driving (from the resistive-input circuit) and high DC precision (from the switched capacitor circuit) without compromise.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If a capacitive input ADC circuit is used, then DC precision is improved, but the ADC becomes difficult to drive and prone to aliasing

Engineering Contradiction:

ImproveDC precisionVSAvoidease to drive

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The system separates the DC precision function (handled by the switched capacitor ADC circuit) from the ease-of-driving function (handled by the resistive-input ADC circuit). This segmentation allows each circuit to be optimized independently, so the capacitive circuit provides high DC precision without needing to also provide ease of driving.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The aliasing problem and driving difficulty are extracted from the DC precision function and assigned to a separate resistive-input ADC circuit. This allows the switched capacitor circuit to focus solely on providing high DC precision while the resistive circuit handles the anti-aliasing and ease-of-driving requirements.

Inventive Principle:

Principle #2Taking out (Extraction)

3Speed

If a single ADC circuit is used to achieve wide bandwidth, then bandwidth is improved, but DC precision deteriorates

Engineering Contradiction:

ImprovebandwidthVSAvoidDC precision

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The frequency spectrum is segmented into two ranges: wide bandwidth AC signals (handled by the resistive-input ADC) and DC/low-frequency signals (handled by the switched capacitor ADC). This segmentation allows each circuit to be optimized for its frequency range, achieving both wide overall bandwidth and high DC precision that would be impossible in a single circuit.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11251807B1Wide bandwidth ADC with inherent anti-aliasing and high DC precision

Publication Date: 2022.02.15 ANALOG DEVICES INT UNLTD CO

AI summary

A wide bandwidth ADC circuit that combines a resistive-input continuous-time sigma-delta ADC circuit with a second ADC circuit having a switched capacitor input. The combination of these two ADC circuits can achieve an easy-to-drive, alias free, wide bandwidth ADC that has excellent DC precision.