Mobility-Based Relaxation Oscillator With PTAT Frequency Compensation

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Solution Overview

Problem

Existing relaxation oscillators suffer from frequency variations due to manufacturing process variations in resistance and capacitance, leading to inaccuracies, and current compensation methods like trim bits increase chip area and testing costs.

Innovation Solution

A relaxation oscillator architecture that bases frequency on electron mobility and uses proportional to absolute temperature (PTAT) current for temperature compensation, eliminating the need for trim bits and reducing variations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If trim bits are used for frequency compensation, then frequency accuracy is improved, but chip area and testing costs increase

Engineering Contradiction:

Improvefrequency accuracyVSAvoidchip area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent extracts the temperature compensation function from external trim bits and implements it internally using PTAT current generation within the oscillator circuit itself. This eliminates the need for external compensation components while maintaining frequency accuracy.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The oscillator circuit generates its own PTAT current for temperature compensation, making the system self-sufficient. The circuit uses internal transistors and current mirrors to create the compensation current without requiring external trim bits or additional testing infrastructure.

Inventive Principle:

Principle #25Self-service

2Device complexity

If resistance and capacitance values are used for frequency determination, then oscillator operation is simplified, but manufacturing process variations cause frequency inaccuracies

Engineering Contradiction:

Improveoscillator operation simplicityVSAvoidfrequency accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The patent changes the fundamental parameter used for frequency determination from RC time constants to electron mobility-based current ratios. By using the relationship between carrier mobility and temperature, the circuit achieves frequency stability that is insensitive to manufacturing variations in passive components.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional mechanical/electrical RC timing mechanism with a semiconductor physics-based approach using carrier mobility characteristics. This substitution leverages the inherent temperature dependence of electron mobility in semiconductors to achieve temperature compensation.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If external compensation methods are used, then frequency accuracy is improved, but chip area and testing costs increase

Engineering Contradiction:

Improvefrequency accuracyVSAvoidtesting costs

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent extracts the temperature compensation function from external test and trim infrastructure and implements it internally through PTAT current generation. This eliminates the need for external compensation methods and their associated testing costs.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #25Self-service

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

The oscillator achieves accurate frequency control with reduced manufacturing variations and eliminates the need for external compensation methods, thereby minimizing chip area and testing costs.

Implementation Method 1

the first current source configured to provide a proportional to absolute temperature (PTAT) current

Methodology Applied

Scientific EffectProportional to Absolute Temperature (PTAT) effect:

Data Source

PatentUS20250343508A1Oscillator frequency based on mobility and PTAT temperature compensation

Publication Date: 2025.11.06 TEXAS INSTRUMENTS INC

AI summary

In an example, a system includes a first transistor having a first terminal coupled to a current mirror and a control terminal coupled to a first current source and a resistor. The system includes a second transistor having a first terminal coupled to the current mirror, a second terminal coupled to a second terminal of the first transistor, and a control terminal coupled to the resistor and a second current source. The system includes a third transistor having a first terminal coupled to a voltage terminal, a second terminal coupled to the control terminal of the second transistor, and a control terminal coupled to the first terminal of the second transistor. The system includes a fourth transistor having a control terminal coupled to the current mirror, first and second terminals coupled to one another and to the second terminal of the first transistor.