MOS Current-Mode Thermal Sensor for Low Power Temperature Measurement

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Solution Overview

Problem

Conventional thermal sensors for micro-processors face challenges in achieving high accuracy and low power consumption while being sensitive to process variations and MOS mismatch, leading to reduced linearity and increased complexity, which is costly and inefficient for volume production.

Innovation Solution

A MOS-based current-mode thermal sensor that generates PTAT and CTAT currents, utilizing a nonlinear feedback loop and a SAR-type ADC to provide a digital output, is developed, which is less sensitive to process variations and allows for low voltage operation, high linearity, and compatibility with future technology scaling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional BJT-based thermal sensors with ADC and reference are used, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidsensor circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent extracts only the essential temperature sensing function by using a simple PTAT current generator and comparator circuit, removing the complex ADC and reference voltage generator while maintaining measurement capability through direct current comparison

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of converting temperature to voltage and then to digital signal through complex ADC, the patent inverts the approach by directly comparing PTAT current with a reference current to generate digital output, simplifying the conversion path

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If conventional BJT-based thermal sensors are used, then measurement precision is improved, but manufacturing precision deteriorates due to sensitivity to process variations and MOS mismatch

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidprocess variation sensitivity

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent changes the sensing parameter from voltage (Vbe) to current (PTAT current), which has better matching characteristics and is less sensitive to process variations and MOS device mismatch, improving manufacturing precision

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a feedback mechanism where the PTAT current is continuously compared with a reference current, and the comparison result is used to adjust the sensing operation, compensating for process variations and improving measurement precision

Inventive Principle:

Principle #23Feedback

3Measurement precision

If conventional BJT-based thermal sensors are used, then measurement precision is improved, but use of energy increases

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent uses simple current mirrors and basic comparator circuits that consume minimal power, replacing the energy-intensive ADC and reference voltage generator, achieving acceptable measurement precision with significantly reduced power consumption

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent employs periodic sampling of the PTAT current and reference current comparison, rather than continuous conversion, reducing the average power consumption while maintaining measurement precision through adequate sampling frequency

Inventive Principle:

Principle #19Periodic action

4Device complexity

If MOS-based current-mode thermal sensor is used, then device complexity is reduced, but measurement precision deteriorates due to MOS mismatch sensitivity

Engineering Contradiction:

Improvesensor circuit complexityVSAvoidtemperature measurement accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent uses current as the sensing parameter instead of voltage, and carefully designs the current mirror ratios and reference current to compensate for MOS device mismatch, maintaining measurement precision while using simpler circuit topology

Inventive Principle:

Principle #35Parameter changes

5Measurement precision

If conventional BJT-based thermal sensors are used, then measurement precision is improved, but area increases

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidsensor silicon area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent extracts only the minimal necessary components for temperature sensing - a PTAT current generator and a comparator - removing the large-area ADC and reference voltage generator, achieving acceptable precision with significantly reduced silicon area

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the temperature sensing function with the current comparison function in a single integrated circuit block, eliminating the need for separate ADC and reference voltage generation circuits, reducing overall sensor area

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS9557226B2Current-mode digital temperature sensor apparatus

Publication Date: 2017.01.31 TAHOE RES LTD

AI summary

Described is a current-mode thermal sensor apparatus which comprises: a first transistor with a gate terminal coupled to a first node; a second transistor with a gate terminal coupled to a second node; a first resistor coupled to the first and second nodes; a second resistor coupled to the first node and a supply node; and a diode coupled to the second node and the supply node.