Time-Interleaved ADC FIR Equalization for Sub-Converter Mismatch

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Solution Overview

Problem

Time interleaved analog-to-digital converters (TI ADC) face issues with sub-converter mismatches, such as offset, gain, and skew mismatches, which deteriorate sampling quality and require costly calibration structures that are limited by process mismatches and thermal or aging drifts.

Innovation Solution

A digital finite impulse response (FIR) equalization filtering unit is used in TI ADCs, with separate FIR sub-filters for each sub-converter, adapting coefficients via recursive least mean squares (LMS) to compensate for mismatches and inter-symbol interference, employing weighted average gain correction and sub-converter specific mismatch compensation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If multiple sub-converters are used in a time interleaved ADC to achieve high sampling rate, then the sampling frequency is improved, but sub-converter mismatches (offset, gain, skew) deteriorate sampling quality

Engineering Contradiction:

Improvesampling frequencyVSAvoidsampling quality

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

A digital filter is introduced as an intermediary component between the sub-converters and the output to compensate for their mismatches. The filter processes the combined signal from multiple sub-converters and corrects offset, gain, and skew errors, thereby maintaining high sampling quality despite the presence of multiple imperfect sub-converters operating at high speed

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention adjusts digital filter parameters (coefficients) to compensate for sub-converter mismatches. By dynamically changing filter parameters based on detected mismatch characteristics, the system corrects sampling quality degradation while maintaining the high sampling frequency achieved through multiple sub-converters

Inventive Principle:

Principle #35Parameter changes

2Manufacturing precision

If analog calibration structures are used to correct sub-converter mismatches, then sampling quality is improved, but device complexity and cost increase

Engineering Contradiction:

Improvesampling qualityVSAvoidcalibration structure

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The invention replaces complex analog calibration structures with a digital filtering approach. Instead of using additional analog components and circuits to calibrate sub-converters, the system uses digital signal processing techniques to correct mismatches, significantly reducing device complexity and cost while maintaining sampling quality

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The digital filter is designed to automatically adapt and compensate for sub-converter mismatches without requiring external calibration procedures. The system performs self-correction by detecting mismatch characteristics and adjusting filter parameters accordingly, eliminating the need for costly and complex external calibration structures

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS10333538B1Time interleaved ADC adaptive filtering

Publication Date: 2019.06.25 STMICROELECTRONICS SRL

AI summary

The present disclosure is directed to a method and system for compensating mismatches among sub-converters in a time interleaved analog digital converter structure. A digital finite impulse response (FIR) equalization filtering unit is coupled to outputs of the sub-converters. The FIR filtering unit includes a digital FIR filter dedicated to each sub-converter. The FIR filtering coefficient is adapted specifically for each sub-converter to achieve a compensation for sub-converter mismatches and inter-symbol interference (ISI) equalization.