SiC JFET Level-Shifting Circuit With Diode-Connected Output Stage

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Solution Overview

Problem

Existing JFET circuits face limitations in voltage and temperature sensitivity, particularly in resistive output stages where increasing supply voltage does not adequately compensate for temperature variations, leading to competing sensitivities and reduced performance.

Innovation Solution

The solution involves relocating resistors to the input stage and utilizing diode degenerated JFET sources in the output stage, incorporating an isolated gate-channel diode to create a resistorless output path with a diode stack that compensates for voltage and temperature sensitivities, thereby improving gain and stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If supply voltage is increased in resistive output stages, then voltage sensitivity is improved, but temperature sensitivity worsens

Engineering Contradiction:

Improvevoltage sensitivityVSAvoidtemperature sensitivity

Core Design Contradiction:

PowerVSTemperature

Solution Approach 1:

The output stage is segmented into multiple diode-connected JFETs arranged in series, where each device contributes a portion of the total voltage drop. This segmentation allows the circuit to achieve high voltage sensitivity through the cumulative effect of multiple devices while each individual device operates at lower voltage stress, reducing temperature sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the operating parameters by transitioning from resistive load operation to diode-connected JFET operation. By biasing the JFETs in the diode connection mode and adjusting their gate-source voltages, the circuit achieves voltage sensitivity comparable to high supply voltage operation while maintaining lower actual supply voltage, thereby reducing temperature sensitivity.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If resistors are used in the output stage, then circuit simplicity is maintained, but temperature sensitivity increases

Engineering Contradiction:

Improvecircuit simplicityVSAvoidtemperature sensitivity

Core Design Contradiction:

Device complexityVSTemperature

Solution Approach 1:

The invention substitutes passive resistive elements with active diode-connected JFETs in the output stage. This replacement eliminates the need for precision resistors while providing temperature-compensated voltage drops through the JFETs' inherent characteristics, achieving both circuit simplicity and temperature stability.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The diode-connected JFETs automatically compensate for temperature variations through their own electrical characteristics. The gate-source voltage of each JFET adjusts with temperature to maintain a stable voltage drop, providing self-service temperature compensation without requiring external correction circuits.

Inventive Principle:

Principle #25Self-service

3Temperature

If diode degenerated JFET sources are used in the output stage, then temperature sensitivity is reduced, but device complexity increases

Engineering Contradiction:

Improvetemperature sensitivityVSAvoiddevice complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The diode-connected JFETs serve multiple functions simultaneously: they provide the output voltage drop, perform temperature compensation, and act as active loads. This multi-functionality reduces the need for separate compensation components, offsetting the increased device count with functional consolidation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention merges the functions of the output stage load and temperature compensation into a single integrated structure using diode-connected JFETs. By combining these functions in one component type, the overall circuit complexity is managed more efficiently than using separate resistors and compensation circuits.

Inventive Principle:

Principle #5Merging (Combining)

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 configuration results in low temperature sensitivity and enhanced pull-up capability, with improved symmetrical rise and fall times in logic circuits, effectively managing threshold voltage shifts and maintaining performance across varying conditions.

Implementation Method 1

using diode degenerated JFET sources in the output stage

Methodology Applied

Scientific EffectDiode junction forward bias: Diode

Implementation Method 2

Integrated-Series Forward-biased JFET Gate-to-Channel Diode Junctions

Methodology Applied

Scientific EffectJFET gate-to-channel diode junction: Diode

Implementation Method 3

the voltage and temperature sensitivities compensate instead compound. Most importantly, the level shifting action of the diode stack in the output stage exhibits a very low temperature sensitivity

Methodology Applied

Scientific EffectTemperature sensitivity compensation:

Implementation Method 4

By moving the resistors to the input (inverting) stage and using diode degenerated JFET sources in the output stage, the voltage and temperature sensitivities compensate instead compound

Methodology Applied

Scientific EffectResistive voltage division: Electrical Resistance

Data Source

PatentUS11838021B1SiC jfet logic output level-shifting using integrated-series forward-biased jfet gate-to-channel diode junctions

Publication Date: 2023.12.05 BARLOW MATTHEW

AI summary

An improved electrical circuit for logic output level shifting using SiC JFETs with resistors on the input, inverting, stage and using diode degenerated JFET sources in the output stage.