MOS Voltage Reference Using Flipped-Gate FETs for Temperature Stability

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Solution Overview

Problem

Existing reference signal generators face challenges in providing a stable, temperature-independent, and process-variation-resistant reference voltage or current signal, with bandgap-type generators susceptible to substrate noise and work function difference-type generators exhibiting temperature dependence.

Innovation Solution

A reference signal generator circuit utilizing a standard MOS device and a work function-modified or flipped-gate nMOS device, where the devices are biased to have different current densities, producing an output signal that is temperature-compensated and stable over process-related variations, using a first transistor coupled between a supply node and an output node, and a flipped-gate transistor between the output node and a reference node, with a bias current source adjusting the current density in the flipped-gate transistor.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If a bandgap-type reference signal generator is used, then a stable reference signal can be provided, but the circuit becomes susceptible to substrate noise

Engineering Contradiction:

Improvereference signal stabilityVSAvoidsubstrate noise susceptibility

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the bipolar junction transistor (BJT) based bandgap reference circuit with a metal oxide semiconductor (MOS) device based reference circuit. This substitution eliminates the substrate noise susceptibility inherent in BJT circuits while maintaining reference signal stability through the MOS device's electrical characteristics and work function differences.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent utilizes differences in work function parameters between MOS devices with different gate materials (e.g., polysilicon vs. metal gates) to generate the reference signal. By changing the gate work function parameter, the circuit achieves temperature-independent reference voltage generation without requiring complex BJT-based bandgap circuitry.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If a work function difference-type reference signal generator is used, then power consumption is reduced, but temperature dependence compromises accuracy

Engineering Contradiction:

Improvepower consumptionVSAvoidtemperature independence

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent introduces a specific circuit configuration using MOS devices with different work functions as intermediaries to convert temperature-dependent threshold voltage differences into a temperature-independent reference voltage. The circuit uses current mirrors and voltage division to mediate between the temperature-dependent device characteristics and the temperature-stable reference output.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs a composite structure combining MOS devices with different gate materials (polysilicon and metal gates) to create a reference circuit that leverages the complementary characteristics of each material. This composite approach enables low power consumption while achieving temperature independence through the differential work function characteristics.

Inventive Principle:

Principle #40Composite materials

3Stability of the object's composition

If MOS devices with different work functions are used, then temperature independence is achieved, but device complexity increases

Engineering Contradiction:

Improvetemperature independenceVSAvoidcircuit structure

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The patent divides the reference circuit into distinct functional segments: a first MOS device with a first work function, a second MOS device with a second work function, and associated biasing circuitry. This segmentation allows each component to be optimized independently while maintaining overall circuit simplicity and achieving temperature independence through the combined operation of the segmented elements.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS11687111B2Reference generator using FET devices with different gate work functions

Publication Date: 2023.06.27 ANALOG DEVICES INT UNLTD CO

AI summary

A reference signal generator circuit can be configured to provide a temperature-compensated voltage reference signal at an output node. The reference signal generator can include a diode-connected first FET device coupled between a supply node and the output node, and a flipped-gate transistor coupled between the output node and a reference node. The reference signal generator can include a bias current source configured to provide a bias current to the output node to adjust a current density in the flipped-gate transistor relative to a current density in the first transistor.