Negative Bootstrap Level Shifter for Low-Side Floating Voltage

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

High-voltage half-bridge switching circuits face challenges in transferring control signals across different voltage domains, particularly when the floating supply voltage is lower than the system ground, leading to issues with noise immunity and correct signal transfer, especially when driving GaN transistors.

Innovation Solution

A negative bootstrap circuit is implemented using capacitors and buffers to generate a negative voltage at the ground reference, allowing for the transfer of command signals across voltage domains by synchronously shifting the ground reference with the activation of commanded current generators, ensuring reliable signal transfer even when the floating supply is lower than the system ground.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional level shifter is used to transfer signals from a first voltage domain to a second voltage domain, then signal transfer is possible, but noise immunity deteriorates and correct signal transfer cannot be ensured when the floating supply voltage is lower than the system ground

Engineering Contradiction:

Improvesignal transfer correctnessVSAvoidnoise immunity

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent inverts the conventional approach by introducing a negative voltage reference instead of relying on a positive floating supply. The level shifter uses a negative voltage domain (-VCC) to establish a proper reference potential, allowing correct signal transfer even when the floating supply voltage is below ground potential. This inversion of the voltage reference strategy resolves the noise immunity and signal correctness issues.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces a negative voltage reference domain as an intermediary between the first voltage domain (GND to VCC) and the second voltage domain (floating supply). This intermediate negative voltage domain acts as a mediator that enables proper signal level translation while maintaining noise immunity, even when the floating supply voltage is lower than ground.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If the floating supply voltage is allowed to drop below system ground to extend operating range, then adaptability improves, but noise immunity and signal transfer correctness deteriorate

Engineering Contradiction:

Improveoperating voltage rangeVSAvoidsignal transfer correctness

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent allows the floating supply to operate below ground potential by introducing a negative voltage reference domain. The level shifter is designed to handle voltage differences between the first voltage domain (with GND reference) and the second voltage domain (with negative voltage reference), enabling the floating supply to operate in an extended voltage range while maintaining signal transfer correctness through proper reference potential management.

Inventive Principle:

Principle #13The other way round (Inversion)

3Adaptability or versatility

If the floating supply voltage is allowed to drop below system ground to extend operating range, then adaptability improves, but noise immunity deteriorates

Engineering Contradiction:

Improveoperating voltage rangeVSAvoidnoise immunity

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a negative voltage reference domain that inverts the conventional positive reference approach. This allows the floating supply to operate below ground potential while maintaining noise immunity, as the negative reference provides a stable potential baseline that prevents noise interference even in extended voltage operating conditions.

Inventive Principle:

Principle #13The other way round (Inversion)

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 enhances noise immunity and ensures correct signal transfer across voltage domains, maintaining system functionality even when the floating supply voltage is below a certain threshold, thereby addressing limitations in existing level shifter designs.

Implementation Method 1

a negative bootstrap circuit including at least a pump capacitor arranged between the current generators and the first ground reference and configured to shift at a negative voltage said first ground reference synchronically with the activation of the respective commanded current generator

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS20240186884A1Circuit to transfer a signal between different voltage domains and corresponding method to transfer a signal

Publication Date: 2024.06.06 STMICROELECTRONICS SRL

AI summary

A circuit includes a current path and a negative bootstrap circuitry coupled to the current path. The current path is coupled between a floating voltage and a reference ground, and includes a current generator coupled through a resistor to the floating voltage at a first node of the current generator. The current generator is controlled by a pulse signal. The negative bootstrap circuitry includes a pump capacitor coupled to a second node of the current generator and to the reference ground. The pump capacitor is configured to provide a negative voltage at the second node of the current generator based on the pulse signal.