DDR2 PCB Layout for Space Memory Bandwidth and Lower Voltage
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Solution Overview
Problem
Existing printed circuit boards used in space applications, such as the SpaceCube 2.0™ processor card, rely on outdated DDR1 SDRAM memory technology that is no longer suitable due to end-of-life issues and insufficient memory bandwidth for modern space missions, requiring an upgrade to support increased data processing demands.
Innovation Solution
A radiation-hardened single board computer system with a unique memory design and layout featuring dual DDR2 SDRAMs on both sides of the printed circuit board, a high-performance reconfigurable FPGA, and a symmetrical layer stack-up to minimize dimensions and reduce operating voltage, along with internal scrubbing and error correction mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DDR1 SDRAM memory is used in the printed circuit board, then the system can maintain compatibility with existing space-qualified components, but the memory bandwidth is insufficient for modern space missions and the memory technology has reached end of life
Solution Approach 1:
The patent transitions from DDR1 to DDR2 memory technology, changing the memory interface parameters including voltage (from 2.5V to 1.8V), data rate, and pinout configuration. This parameter change enables access to newer, faster memory technology while maintaining space-qualified reliability through careful selection of radiation-hardened DDR2 components.
2Productivity
If the printed circuit board layout is changed to accommodate DDR2 memory upgrades, then the memory bandwidth and processing capability are improved, but the device complexity and design difficulty increase significantly
Solution Approach 1:
The patent utilizes the third dimension by implementing a multi-layer PCB stack-up with twenty-two symmetrical layers. This vertical dimensionality allows complex signal routing and power/ground distribution without increasing the board's planar footprint, thereby managing complexity while supporting enhanced memory capabilities.
Solution Approach 2:
The patent employs asymmetrical PCB layout strategies where high-speed DDR2 memory signals are routed on specific layers with dedicated reference planes, while lower-speed control signals use different routing paths. This asymmetrical approach optimizes signal integrity for critical high-speed paths while simplifying routing for less demanding signals.
3Use of energy by moving object
If DDR2 SDRAM with reduced operating voltage is implemented, then power consumption is reduced, but the interface signals and voltage requirements differ from DDR1, complicating the printed circuit board design
Solution Approach 1:
The patent segments the power distribution system by providing separate voltage regulation domains for DDR2 memory (1.8V) and other system components. This segmentation allows the DDR2 interface to operate at its optimal lower voltage while other parts of the system maintain their existing voltage requirements, managed through dedicated voltage regulator modules.
Data Source
AI summary
The present invention relates to a single board computer system with an improved memory and layout. The unique layout of the printed circuit board of the present invention allows for different parts to be placed in a back-to-back configuration to minimize the dimensions of the printed circuit board. This includes a high-performance radiation-hardened reconfigurable FPGA, for processing computation-intensive space systems, disposed on both sides of the printed circuit board. Four dual double data rate synchronous dynamic random-access memories (DDR2 SDRAMs) disposed on both the top side and on the bottom side of the printed circuit board reduce an operating voltage of said printed circuit board. A layout stack-up of the printed circuit board includes twenty-two symmetrical layers including ten ground layers, four power layers, six signal layers, a top layer, and a bottom layer.