CT ADC Transfer Function Estimation Using Digital Cross-Correlation

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Solution Overview

Problem

Conventional analog-to-digital converters (ADCs) face errors in transfer function estimation due to energy leakage of test signals, which limits noise spectral density (NSD) and signal-to-noise ratio (SNR) performance, especially in high-performance and high-speed applications.

Innovation Solution

Implementing a digital estimation of transfer functions by using a circuit that generates cross-correlation outputs from test signals and backend ADC outputs to accurately estimate the transfer function, reducing errors and energy leakage, thereby improving NSD and SNR.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional analog-to-digital converters are used for high-speed and high-performance applications, then conversion speed and basic functionality are achieved, but transfer function estimation accuracy deteriorates due to energy leakage of test signals

Engineering Contradiction:

Improvetransfer function estimation accuracyVSAvoidenergy leakage of test signals

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

The patent extracts and removes the harmful energy leakage component from the test signal by implementing a digital estimation approach that separates the desired transfer function measurement from the parasitic energy leakage, thereby improving measurement accuracy without being constrained by the energy loss issue

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the conventional analog-based transfer function estimation method with a digital estimation approach, substituting analog signal processing with digital signal processing to achieve more accurate transfer function measurement by eliminating analog energy leakage effects

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If conventional ADC architecture is used, then device simplicity is maintained, but noise spectral density and signal-to-noise ratio performance deteriorate

Engineering Contradiction:

Improvenoise spectral density and signal-to-noise ratio performanceVSAvoidADC architecture complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces a digital estimation module as an intermediary component that processes the test signal and backend ADC output to accurately estimate the transfer function, acting as a mediator between the test signal injection and the final performance measurement, thereby improving reliability without requiring fundamental architectural changes

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the estimation approach from analog domain to digital domain, transforming the transfer function estimation parameter measurement method to achieve better noise spectral density and signal-to-noise ratio performance while maintaining compatible hardware architecture

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11218158B1Digital estimation of transfer functions in continuous-time analog-to-digital converters

Publication Date: 2022.01.04 ANALOG DEVICES INT UNLTD CO

AI summary

In one aspect, a transfer function (TF) estimation circuit configured to generate an estimate of a TF undergone by signals between an input of a digital-to-analog converter (DAC) of a feedforward path of a continuous-time (CT) stage of an analog-to-digital converter (ADC) and an output of a backend ADC of the ADC is disclosed. The TF estimation circuit includes one or more circuits configured to generate a first cross-correlation output by cross-correlating digital versions of signals based on a test signal provided to the CT stage and an output signal of the backend ADC, generate a second cross-correlation output by cross-correlating digital versions of signals based on the test signal and an output signal of a quantizer of the feedforward path of the CT stage, and generate the estimate of the TF based on the first and second cross-correlation outputs.