DRAM Refresh Control Device for Wireless Receiver EMI Reduction

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Solution Overview

Problem

Conventional refresh control methods for DRAMs in wireless receivers result in high EMI noise due to constant refresh trigger cycles, degrading reception quality by propagating noise through common GND lines and affecting tuner units.

Innovation Solution

A refresh control device with an arbitration unit and a trigger generating unit that generates non-constant refresh triggers to satisfy refresh-rate requirements, reducing noise levels by varying the cycle of refresh operations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If constant refresh trigger cycles are used for DRAM refresh operations, then the refresh operation is simple to implement and maintains data reliably, but high EMI noise is generated that degrades wireless signal reception quality

Engineering Contradiction:

Improvedata holding reliabilityVSAvoidEMI noise affecting reception quality

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The refresh trigger cycle is changed from constant to variable. The arbitration unit dynamically adjusts the refresh trigger timing based on memory access requests, creating non-uniform intervals between refresh operations. This dynamic approach spreads the spectral energy of refresh triggers across a wider frequency range, reducing peak EMI noise levels while maintaining data refresh reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The cycle period of refresh triggers is changed as a parameter. Instead of fixed periodic refresh, the system varies the time interval between consecutive refresh triggers. This parameter change transforms the refresh operation from a predictable periodic signal (high EMI) to a more random pattern (lower EMI), while still satisfying the minimum refresh rate requirements for data retention.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If refresh operations are performed at fixed intervals, then the timing is predictable and easy to control, but noise peaks occur at specific frequencies that interfere with tuner units

Engineering Contradiction:

Improverefresh control simplicityVSAvoidnoise peaks from constant cycle

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The refresh control transitions from static fixed-interval timing to dynamic variable-interval timing. The arbitration unit introduces randomness in refresh trigger timing by adjusting intervals based on current memory access patterns. This dynamic control eliminates fixed frequency noise peaks while maintaining adequate refresh coverage through adaptive timing adjustment.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system maintains periodic refresh action (still performing refresh at regular-ish intervals) but varies the period length. Instead of identical periodic cycles, the period between refresh operations changes dynamically. This preserves the essential periodic nature needed for reliable memory operation while eliminating the harmful fixed-frequency characteristics that cause EMI noise peaks.

Inventive Principle:

Principle #19Periodic action

3Device complexity

If refresh triggers are generated in constant cycles, then the arbitration logic is simple, but large currents flow during pre-charging causing power supply variation and GND line noise

Engineering Contradiction:

Improvearbitration logic complexityVSAvoidpower supply variation and GND noise

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

The arbitration logic becomes dynamic rather than static. The system uses a simple arbitration mechanism that adjusts refresh trigger timing based on memory access requests, introducing variability without complex control logic. This dynamic adjustment spreads out the high-current pre-charge operations in time, reducing simultaneous current demands and minimizing power supply variation and GND line noise.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system performs refresh operations slightly more frequently or at variable intervals rather than strict minimum intervals. This partial excess in refresh frequency, combined with variable timing, ensures data reliability while distributing the electrical load of pre-charge operations more evenly over time, reducing peak current effects on power supply and ground lines.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS9824741B2Refresh control device, wireless receiver, and semiconductor integrated circuit

Publication Date: 2017.11.21 PANASONIC SEMICON SOLUTIONS CO LTD

AI summary

Provided is a refresh control device including: an arbitration operating unit configured to arbitrate (i) a memory access request for accessing a volatile memory that requires a refresh operation for holding data and (ii) a refresh trigger for requesting execution of the refresh operation; and a trigger generating unit configured to generate refresh triggers in a non-constant cycle to satisfy refresh-rate requirements defining the number of refresh operations necessary to be executed per predetermined period for the volatile memory to hold the data.