Temperature-Dependent Oscillation Circuit for DRAM Self-Refresh

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Solution Overview

Problem

Semiconductor memory devices, such as DRAM, face reduced data retention time and increased leakage current at higher operational temperatures, leading to inefficient self-refresh operations due to fixed refresh periods that do not adapt to temperature changes.

Innovation Solution

An oscillation circuit is designed with an internal voltage generator that produces a voltage varying linearly with temperature, driving an oscillator to generate a variable oscillation signal with frequency changes matching temperature variations, allowing for adaptive self-refresh operations without additional temperature sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If a fixed refresh period is used for self-refresh operations, then the circuit complexity is reduced, but data retention time decreases at higher temperatures due to increased leakage current

Engineering Contradiction:

Improvecircuit complexityVSAvoiddata retention time

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent implements a dynamic refresh period that automatically adjusts with temperature changes. An internal voltage generator produces a voltage that varies linearly with temperature, which in turn modulates the oscillation frequency of the oscillator. This causes the refresh period to decrease as temperature increases, compensating for increased leakage current and maintaining data retention without requiring external temperature sensors or complex control logic.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operational parameters of the oscillation circuit based on temperature. The internal voltage generator converts temperature variations into voltage changes, which directly affect the oscillation frequency. This parameter change approach allows the refresh rate to adapt to temperature conditions, solving the data retention problem while keeping the overall system simple.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the refresh frequency is increased to maintain data retention at higher temperatures, then data retention time is improved, but power consumption increases

Engineering Contradiction:

Improvedata retention timeVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The system dynamically adjusts the refresh frequency based on actual temperature conditions rather than operating at a fixed high frequency. At lower temperatures where leakage current is minimal, the refresh frequency naturally decreases, reducing unnecessary refresh operations and lowering power consumption. At higher temperatures, the frequency increases automatically to maintain data retention, optimizing the balance between reliability and energy usage.

Inventive Principle:

Principle #15Dynamics

3Adaptability or versatility

If additional temperature sensors are added to enable temperature-adaptive refresh operations, then adaptability is improved, but device complexity increases

Engineering Contradiction:

Improvetemperature adaptabilityVSAvoidcircuit complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The oscillation circuit uses its own internal components (internal voltage generator and oscillator) to sense and respond to temperature changes. The internal voltage generator inherently produces a voltage that varies with temperature, eliminating the need for external temperature sensors. This self-service approach provides temperature adaptability while keeping the circuit simple and integrated within the existing memory device.

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

This solution improves data retention and reduces power consumption by ensuring self-refresh operations are frequency-adjusted with temperature, minimizing unnecessary refreshes at lower temperatures and enhancing overall memory performance.

Implementation Method 1

an internal voltage generator which receives an external voltage and generates an internal voltage based on the external voltage. The internal voltage varies in linearly with the operational temperature.

Methodology Applied

Scientific EffectTemperature-dependent voltage generation: Thermocouple

Implementation Method 2

an oscillator which generates a variable oscillation signal based on the internal voltage. A period of the variable oscillation signal varies in linearly with the operational temperature.

Methodology Applied

Scientific EffectVoltage-controlled oscillation frequency:

Data Source

PatentUS8218375B2Oscillation circuits having temperature-dependent frequency generation and semiconductor memory devices having temperature-dependent self refresh rate

Publication Date: 2012.07.10 SAMSUNG ELECTRONICS CO LTD

AI summary

An oscillation circuit includes an internal voltage generator and an oscillator. The internal voltage generator receives an external voltage and generates an internal voltage based on the external voltage. The internal voltage varies in linearly with an operational temperature. The oscillator generates a variable oscillation signal based on the internal voltage. A period of the variable oscillation signal varies in linearly with the operational temperature.