Two-Stage SAR ADC Gain Calibration for Background Conversion

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Solution Overview

Problem

Two-stage SAR ADCs require calibration to achieve optimal performance, but existing calibration methods interrupt normal operation and do not account for time-varying environmental changes, limiting their effectiveness.

Innovation Solution

A method for gain calibration in SAR ADCs that allows continuous operation by adding only one additional comparison step in the second stage ADC, enabling background calibration and addressing DAC mismatch and gain errors without interrupting normal operation, using a control module to determine the presence and direction of gain errors through comparison of the least significant bit and calibration bit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional calibration methods are used to correct gain errors and DAC mismatch, then measurement precision is improved, but the normal operation of the SAR ADC must be interrupted

Engineering Contradiction:

Improvegain calibration accuracyVSAvoidcontinuous conversion capability

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The calibration process is performed in advance during manufacturing or initialization, storing the calibration results (gain correction values and DAC mismatch correction values) in memory. This preliminary calibration eliminates the need to interrupt normal operation for calibration, as the correction data is already available for immediate use during conversion operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A separate calibration module is introduced as an intermediary component that performs calibration operations independently from the main SAR ADC conversion path. This calibration module can operate without interrupting the normal conversion process, using stored calibration data to correct gain errors and DAC mismatch while the main converter continues its measurement function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If calibration is performed frequently to account for time-varying environmental changes, then reliability is improved, but operation interruption increases

Engineering Contradiction:

Improveperformance stability under environmental variationsVSAvoidcalibration downtime

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

Calibration data is pre-acquired and stored in memory to account for environmental variations. The calibration module retrieves and applies these pre-stored correction values during operation without interruption, allowing the system to adapt to environmental changes while maintaining continuous conversion capability.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The calibration function is designed to operate in the background or during idle periods without interrupting the main conversion function. The calibration module continuously monitors environmental conditions and applies appropriate calibration corrections while the SAR ADC maintains its normal measurement operations, ensuring both reliability and continuous productivity.

Inventive Principle:

Principle #20Continuity of useful action

3Productivity

If background calibration is implemented to maintain continuous operation, then productivity is improved, but device complexity increases

Engineering Contradiction:

Improvecontinuous conversion capabilityVSAvoidcalibration system structure

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The calibration module is designed to perform multiple calibration functions (gain calibration and DAC mismatch calibration) using a unified approach. The same calibration circuitry and control logic are used for both calibration types, reducing overall system complexity while enabling continuous operation with comprehensive error correction.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The calibration system is designed to be self-contained and self-regulating, automatically performing calibration operations without requiring external intervention or complex control sequences. The calibration module independently manages its own operation, retrieves calibration data from memory, and applies corrections automatically, minimizing the burden on the main system and reducing overall complexity.

Inventive Principle:

Principle #25Self-service

Data Source

PatentEP3334047B1A method of gain calibration in a two-stage pipelined successive approximation register analog-to-digital converter and a two-stage pipelined successive approximation register analog-to-digital converter

Publication Date: 2021.04.21 STICHTING IMEC NEDERLAND

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AI summary

A method of gain calibration in a SAR ADC (700) comprising the steps of: determining a number of bits of an analog input signal (V1N); detecting if a binary code determined from the analog input signal (VIN) matches at least one trigger code; using at least one setting code to determine a calibration residue signal (V*RES) and a calibration bit (B*LSB); analyzing a least significant bit of the digital signal (COUT) and the calibration bit (B*LSB); determining an indication of a presence of gain error in the gain module; and calibrating the gain error. As the determination of the calibration bit (B*LSB) requires only one additional comparison, when compared to the normal operation, the normal operation does not need to be interrupted. Therefore, the calibration can be done in the background and, as such, can be performed frequently thereby taking into account time-varying changes due to environmental effects.