SAR ADC Reference Topology for High-Voltage Capacitor Stress

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Solution Overview

Problem

Analog-to-digital converters (ADCs) face challenges in handling high voltage analog input signals due to low voltage ratings of capacitors, which can lead to voltage drops exceeding capacitor ratings, potentially causing failure and limiting the maximum voltage range for analog input signals.

Innovation Solution

The implementation of a high-side reference voltage supply, coupled via a reference switch to the capacitor terminal, reduces the likelihood of capacitor failure by maintaining a lower voltage drop across capacitors during sampling and comparator auto-zero phases, allowing for higher maximum voltage ranges for analog input signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional capacitor coupling method is used during sampling and comparator auto-zero phases, then the ADC can operate with standard capacitor sizes, but the voltage drop across capacitors exceeds their voltage ratings, leading to potential failure and limiting the maximum voltage range for analog input signals

Engineering Contradiction:

Improvecapacitor reliabilityVSAvoidanalog input voltage range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

A middle reference voltage supply is introduced as an intermediary between the high voltage analog input signal and the capacitors. During sampling and comparator auto-zero phases, this middle reference voltage is coupled to the first terminal of each capacitor, serving as a mediator that prevents excessive voltage drops across the capacitors while still allowing the ADC to handle high voltage analog input signals.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the maximum voltage range for analog input signals is increased, then the ADC can handle higher voltage signals, but the voltage drop across capacitors during sampling phases exceeds their voltage ratings, causing potential capacitor failure

Engineering Contradiction:

Improveanalog input voltage rangeVSAvoidcapacitor reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The middle reference voltage is preliminarily coupled to the capacitors during sampling and comparator auto-zero phases before the actual conversion phase. This preliminary action establishes a safe voltage reference point for the capacitors, preventing excessive voltage drops that would occur if high voltage analog input signals were directly coupled to the capacitors during these phases.

Inventive Principle:

Principle #10Preliminary action

3Reliability

If capacitor size is increased to handle higher voltage ranges, then the voltage rating capacity is improved, but the device area and complexity increase

Engineering Contradiction:

Improvevoltage handling capabilityVSAvoidcapacitor area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

Instead of changing the physical size of the capacitors, the invention changes the voltage parameter by introducing a middle reference voltage supply. This allows the same capacitor size to handle higher voltage ranges by preventing excessive voltage drops across the capacitors during critical phases, rather than increasing capacitor size to accommodate higher voltages.

Inventive Principle:

Principle #35Parameter changes

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 approach enables ADCs to handle higher voltage ranges without increasing capacitor size, reducing the risk of failure and allowing for more robust operation within smaller process nodes, thus supporting legacy voltage ranges while minimizing noise and performance limitations.

Implementation Method 1

a first reference switch coupled between the second reference voltage supply input and the input node of the comparator

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

a second reference switch coupled between the first reference voltage supply input and the first terminal of each capacitor of the set of capacitors

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 3

a third switch coupled between the input node of the comparator and the first terminal of each capacitor of the set of capacitors

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 4

a comparator comprising an input node

Methodology Applied

Scientific EffectVoltage comparison:

Implementation Method 5

a set of capacitors, where each capacitor of the set of capacitors comprises a first terminal

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11646750B2Successive approximation analog-to-digital converter

Publication Date: 2023.05.09 TEXAS INSTRUMENTS INC

AI summary

An analog-to-digital converter (ADC) is provided. In some examples, the ADC includes a first reference voltage supply input, a second reference voltage supply input, a comparator comprising an input node, and a first reference switch coupled between the second reference voltage supply input and the input node of the comparator. The ADC also includes a set of capacitors, where each capacitor of the set of capacitors comprises a first terminal. In addition, the ADC includes a second reference switch coupled between the first reference voltage supply input and the first terminal of each capacitor of the set of capacitors. The ADC further includes a third switch coupled between the input node of the comparator and the first terminal of each capacitor of the set of capacitors.