Inter-Stage Gain Calibration for Open-Loop Residue Amplifiers

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Solution Overview

Problem

High-accuracy analog-to-digital converter (ADC) circuits require frequent calibration due to variations in temperature and manufacturing processes, and existing calibration methods are either costly, interruptive, or inefficient, especially when using open-loop amplifiers which struggle with stability under environmental changes.

Innovation Solution

Implement background calibration techniques that inject a controlled perturbation between conversion cycles to measure and estimate the gain of residue amplifiers, allowing open-loop amplifier circuits to be used for better power efficiency and faster error correction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If open-loop amplifier circuits are used as residue amplifiers, then power efficiency is improved, but stability under environmental changes deteriorates

Engineering Contradiction:

Improvepower efficiencyVSAvoidstability under environmental changes

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The patent applies preliminary action by performing background calibration before normal ADC operation to pre-determine the gain characteristics of the open-loop residue amplifier. The calibration process injects test signals and measures amplifier response in advance, storing calibration data that compensates for environmental variations during actual conversion operations, thus ensuring stability while maintaining power efficiency.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the measured gain information from calibration to adjust and correct the operation of the open-loop residue amplifier. The calibration system continuously monitors amplifier performance and applies correction factors to compensate for drift caused by temperature and manufacturing variations, enabling the open-loop amplifier to maintain stability without requiring closed-loop operation.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If frequent calibration is performed to maintain accuracy, then measurement precision is improved, but productivity deteriorates due to interruptive foreground calibration

Engineering Contradiction:

ImproveADC accuracyVSAvoidconversion throughput

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The patent applies periodic action by performing calibration in the background during normal ADC operation rather than interrupting conversion to perform calibration. The system periodically updates calibration data using test signals injected between conversions or during idle periods, maintaining accuracy without stopping the main conversion pipeline, thus preserving productivity while ensuring measurement precision.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements continuity of useful action by enabling calibration to proceed simultaneously with normal ADC conversion operations. The background calibration process runs continuously in parallel with foreground conversions, utilizing unused time slots and resources to maintain calibration accuracy without interrupting the productive conversion workflow, thereby eliminating the trade-off between precision and productivity.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If background calibration is implemented to reduce interruptive calibration, then productivity is improved, but device complexity increases

Engineering Contradiction:

Improveconversion throughputVSAvoidcalibration circuit complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent applies universality by designing calibration circuits that perform multiple functions: the same hardware infrastructure is used for both normal ADC conversion and calibration operations. The residue amplifier, DAC, and control logic serve dual purposes during calibration mode, eliminating the need for separate dedicated calibration hardware and reducing overall device complexity while enabling continuous background calibration that maintains productivity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS10608655B1Inter-stage gain calibration in double conversion analog-to-digital converter

Publication Date: 2020.03.31 ANALOG DEVICES INC

AI summary

Various background calibration techniques to calibrate inter-stage gain, e.g., in pipelined ADCs, are described to allow open loop amplifier circuits to be used as residue amplifiers for better power efficiency. Using various techniques, a well-controlled perturbation can be injected between two conversions and the actual perturbation after a residue amplifier can be measured. By comparing the actual measurement against an expected value, the gain information of the residue amplifier can be estimated and then calibration can be applied.