SAR ADC Capacitor Array Switching for Reference Rail Stability

Solution Overview

Problem

Successive approximation register (SAR) analog-to-digital converters (ADCs) experience nonlinear memory effects due to large current draws from the reference rail, causing voltage drops that distort subsequent conversions, leading to performance degradation.

Innovation Solution

A capacitor array with a switching network is used to switch capacitors between a supply voltage source and the reference rail, compensating for voltage drops before the next conversion cycle, thereby reducing the need for large capacitors and minimizing current consumption and space requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If large capacitors are used to compensate for reference voltage drops, then voltage stability is improved, but device area and energy consumption increase

Engineering Contradiction:

Improvevoltage stabilityVSAvoiddevice area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The reference voltage compensation function is segmented and integrated into each individual capacitor of the capacitor array. Each capacitor is equipped with switching circuitry that enables it to independently sense and compensate for voltage drops on the reference rail during its specific conversion cycle, eliminating the need for a separate large compensation capacitor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The capacitors in the capacitor array perform dual functions: (1) their primary function as DAC elements for digital-to-analog conversion, and (2) a secondary function as reference voltage compensation elements. This multi-functionality allows the same hardware components to address both conversion and voltage stabilization needs without additional area overhead.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If large capacitors are used to compensate for reference voltage drops, then voltage stability is improved, but energy consumption increases

Engineering Contradiction:

Improvevoltage stabilityVSAvoidenergy consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The reference voltage compensation function is segmented and integrated into each individual capacitor of the capacitor array. Each capacitor is equipped with switching circuitry that enables it to independently sense and compensate for voltage drops on the reference rail during its specific conversion cycle, eliminating the need for a separate large compensation capacitor.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The capacitors in the capacitor array perform dual functions: (1) their primary function as DAC elements for digital-to-analog conversion, and (2) a secondary function as reference voltage compensation elements. This multi-functionality allows the same hardware components to address both conversion and voltage stabilization needs without additional area overhead.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If SAR ADC operates with high speed conversions, then bandwidth is improved, but reference voltage distortion increases due to sequential bit conversions

Engineering Contradiction:

ImprovebandwidthVSAvoidconversion accuracy

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

Each capacitor in the array performs preliminary reference voltage compensation during its specific conversion cycle before subsequent conversions occur. By proactively compensating for voltage drops at the appropriate timing within each conversion cycle, the system maintains reference voltage stability throughout high-speed operation without compromising conversion accuracy.

Inventive Principle:

Principle #10Preliminary action

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This solution effectively mitigates nonlinear memory effects while maintaining high bandwidth and signal-to-noise ratio, offering a more space-efficient and energy-efficient alternative to previous methods.

Implementation Method 1

a capacitor array with a switching network configured to switch one or more capacitors of the capacitor array between a conductor connected to a supply voltage source and a conductor connected to the reference rail

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentEP4472080A1Successive approximation register analog-to-digital converter

Publication Date: 2024.12.04 INTEL CORP

Figure 1
Figure 2
Figure 3

AI summary

A circuit comprising: an analog-to-digital converter configured to generate a digital signal based on a received input voltage and a received reference voltage; a capacitor array; and a switching network configured to switch each capacitor of the capacitor array between a first conductor connected to a supply voltage source, and a second conductor connected to the reference voltage; wherein the analog-to-digital converter comprises a logic configured to control the switching network to selectively switch between the first conductor and the second conductor based on the generated digital signal.