CMOS Temperature Sensor Oscillator Readout Circuit

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Solution Overview

Problem

Conventional CMOS temperature sensors face challenges in achieving high accuracy due to variations in the substrate PNP transistor's temperature coefficient caused by process changes, and they also suffer from high power consumption and large area requirements.

Innovation Solution

A CMOS temperature sensor utilizing a readout circuit that outputs a readout value by comparing voltage values at a capacitor's ends with either an inverse proportional voltage or ground voltage, and a control unit that determines temperature based on the oscillation period of the readout value.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a sigma-delta ADC-based readout circuit is used in a CMOS temperature sensor, then measurement resolution and accuracy are improved, but power consumption increases and circuit area becomes large

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidpower consumption

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent replaces the conventional sigma-delta ADC-based readout circuit with an oscillator-based readout circuit that converts temperature information into oscillation period. This substitution of the measurement mechanism enables accurate temperature sensing while significantly reducing power consumption and circuit area, as the oscillator circuit is inherently more power-efficient and compact than ADC-based systems.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the output parameter from voltage/digital code (ADC output) to oscillation period/frequency. By measuring temperature through the oscillation period of a relaxation oscillator rather than through ADC conversion, the system achieves the same measurement accuracy with much lower power consumption and smaller circuit footprint.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If a sigma-delta ADC-based readout circuit is used in a CMOS temperature sensor, then measurement resolution and accuracy are improved, but circuit area becomes large

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidcircuit area

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If a band gap reference signal and SUBSTRATE PNP transistor are used, then temperature measurement capability is achieved, but accuracy decreases due to process variations in temperature coefficient

Engineering Contradiction:

Improvetemperature measurement accuracyVSAvoidtemperature coefficient stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces the conventional band gap reference-based temperature sensing mechanism with an oscillator-based mechanism. The oscillator's oscillation period naturally varies with temperature through voltage-dependent timing, eliminating the need for SUBSTRATE PNP transistors and band gap references that suffer from process variations. This substitution provides inherent immunity to process-induced temperature coefficient drift.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The oscillator circuit uses its own output signal to control its charging current, creating a self-regulating system where the oscillation period directly reflects temperature without requiring external reference signals. This self-service mechanism eliminates dependence on process-critical components like SUBSTRATE PNP transistors.

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 proposed solution enables accurate temperature measurement while improving power and area efficiency of the CMOS temperature sensor.

Implementation Method 1

a capacitor charging a charge based on a proportional current proportional to a temperature

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

comparing a voltage value at a first end of a capacitor charging a charge based on a proportional current proportional to a temperature with an inverse proportional voltage inversely proportional to the temperature

Methodology Applied

Scientific EffectVoltage comparison: Ohm's Law

Data Source

PatentUS12320714B2CMOS temperature sensor and operating method thereof

Publication Date: 2025.06.03 SOLIDVUE INC

AI summary

Disclosed are a CMOS temperature sensor for measuring a temperature and an operating method thereof. According to an embodiment, the CMOS temperature sensor for measuring the temperature may include a readout circuit that outputs a readout value by comparing a voltage value at a first end of a capacitor charging a charge based on a proportional current proportional to a temperature with an inverse proportional voltage inversely proportional to the temperature or comparing a voltage value at a second end of the capacitor formed at the other side of the first end with a ground voltage; and a control unit that determines a temperature based on an oscillation period of the readout value output from the readout circuit.