RFID Temperature Sensor Linearity Correction via PTAT Current

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Solution Overview

Problem

Conventional frequency ratio digitizing temperature sensors suffer from non-linearity issues due to propagation delays and temperature-dependent characteristics of components, leading to inaccurate digital output signals, and existing solutions either complicate the system or increase costs with external components like crystal oscillators.

Innovation Solution

A frequency ratio digitizing temperature sensor implements linearity correction by adding a correction current proportional to absolute temperature (PTAT) to both the reference and data oscillators, canceling linearity errors through identical application of corrected reference currents, thereby stabilizing the reference frequency and improving measurement accuracy without external components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional frequency ratio digitizing temperature sensors are used, then the system is simple and cost-effective, but linearity errors occur due to propagation delays and temperature-dependent characteristics

Engineering Contradiction:

Improvelinearity accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent converts the harmful propagation delays and temperature-dependent characteristics into a beneficial correction mechanism. By measuring the actual propagation delays and temperature variations, the system generates correction factors that compensate for these effects, transforming the source of error into the means of correction.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent implements feedback by measuring the propagation delays and temperature-dependent characteristics, then using these measurements to generate correction factors that are applied to subsequent measurements. This closed-loop approach continuously improves measurement accuracy by compensating for systematic errors.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If external components like crystal oscillators are added to correct linearity errors, then measurement accuracy improves, but system cost and complexity increase

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidcomponent quantity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent enables the temperature sensor system to self-correct its own errors using internally generated correction factors based on its own propagation delays and temperature-dependent characteristics. This eliminates the need for external correction components while maintaining high measurement accuracy.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent changes the operational parameters of the oscillators by applying correction factors that adjust their frequencies based on measured propagation delays and temperature conditions. This dynamic parameter adjustment compensates for non-linearity without requiring additional hardware components.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If propagation delays are not compensated, then the system operates simply, but digital output signals become inaccurate

Engineering Contradiction:

Improvedigital output accuracyVSAvoidmanufacturing simplicity

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent performs preliminary measurement of propagation delays during manufacturing or initial operation, then uses these pre-measured values to generate correction factors for subsequent measurements. This preliminary action eliminates the need for complex real-time compensation while maintaining accuracy.

Inventive Principle:

Principle #10Preliminary action

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 achieves significant linearity improvement, reducing errors by up to 20 dB and providing stable reference frequencies, thus enhancing the accuracy and cost-effectiveness of temperature measurements.

Implementation Method 1

Conventional frequency ratio digitizing temperature sensors suffer from non-linearity issues due to propagation delays and temperature-dependent characteristics of components

Methodology Applied

Scientific EffectTemperature-dependent electrical characteristics:

Data Source

PatentUS7474230B2RFID temperature logger incorporating a frequency ratio digitizing temperature sensor

Publication Date: 2009.01.06 NAT SEMICON CORP

AI summary

A semi-passive radio frequency identification (RFID) tag being coupled to a battery providing a battery voltage for powering a part of the circuitry of the RFID tag includes an RF communication block receiving and transmitting RF signals, a sensor block including a frequency ratio digitizing temperature sensor for alternately measuring the ambient temperature and the battery voltage, and a control logic block in communication with the RF communication block and the sensor block. The control logic controls the operation of the RF communication block and the sensor block and stores temperature and voltage measurement data generated by the sensor block. In one embodiment, the control logic block of the RFID tag operates based on a system clock and the sensor block provides a reference clock to the control logic block for use in calibrating the system clock of the control logic block.