ADC Bias Generator Offset Voltage Swapping

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Solution Overview

Problem

Analog-to-digital converters (ADCs), particularly successive-approximation-resister (SAR) ADCs, suffer from gain errors due to offset voltages in operational amplifiers, which affect the accuracy of reference voltage generation and subsequent analog-to-digital conversion.

Innovation Solution

A bias generator comprising an operational amplifier, a resistor string, and a control circuit that swaps the offset voltage polarity during consecutive conversions, allowing the ADC to average out the offset voltage effects and reduce gain errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If offset voltage compensation is implemented using operational amplifier, then gain error is reduced, but device complexity increases

Engineering Contradiction:

Improvegain errorVSAvoiddevice complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The offset voltage compensation is segmented into multiple consecutive conversion cycles. The first conversion cycle measures the offset voltage, and the second conversion cycle applies the compensation. This divides the complex compensation process into manageable stages, reducing the instantaneous complexity while achieving gain error reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The offset voltage is measured and stored in advance during the first conversion cycle before the actual compensated conversion occurs in the second cycle. This preliminary measurement action allows the system to prepare compensation data without interfering with the main conversion process, thereby managing complexity effectively.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If offset voltage swapping is performed across consecutive conversions, then measurement precision improves, but loss of time increases

Engineering Contradiction:

Improveaccuracy of reference voltageVSAvoidconversion time

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The offset voltage swapping operates periodically across consecutive conversion cycles. The system alternates between measuring offset voltage in one cycle and applying compensated conversion in the next cycle. This periodic action allows precision improvement while maintaining a predictable and manageable time loss pattern.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The useful action continues across consecutive conversion cycles without interruption. While one cycle is dedicated to offset measurement, the next cycle immediately applies the compensation, ensuring continuous productive operation. This minimizes idle time and reduces overall time loss while maintaining measurement precision.

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentUS9660659B2Apparatus for correcting gain error of analog-to-digital converter

Publication Date: 2017.05.23 SK HYNIX INC

AI summary

A bias generator may include: an operational amplifier, a resister string, and a control circuit. The operational amplifier includes a first input terminal suitable for receiving a bandgap reference voltage, a second input terminal with an offset voltage and an output terminal. The resister string includes at least one resister coupled between a ground terminal and the output terminal of the operational amplifier, suitable for generating bias voltages. The control circuit is coupled between the second input terminal and the resister string, swaps the offset voltage, and selectively provides the offset voltage and the swapped offset voltage to the second input terminal of the operational amplifier.