All embedded Intel® architecture products vary in their uses, but they have one thing in common: the complexity of their design. From an engineer's perspective there are many new and unfamiliar challenges of getting large amounts of electrical, electronic hardware on generally a smaller piece of board/PCB in the case of embedded design.
This white paper discusses some of the major factors that need to be considered in designing an embedded product and the various high-speed digital design concepts that play a vital role in the functionality of the hardware/ product as a whole. This paper will help a designer understand why the electrical signals act so differently on a high-speed design, identify the various problems that may occur in the design, and solve these problems.
In the world of high speed digital design and architecture the following concepts play a major role in deciding the success of a product.
First, the architecture of a system forms an important part of the design equation. Next, designers must get through the schematics and layout of the design. During the layout phase the signal integrity factors such as reflections, ground bounce, crosstalk, power supply noise and EMI factors such as radiation and electrostatic discharge need to be considered before the board is built. The guidelines necessary for the optimal schematic and layout design of the board are provided through the schematic and layout checklists in the product Platform Design Guideline (here on referred to as the PDG).
For a good design a lot of ground work is done before the actual board is built. This is made up of system architecture, schematics and layout of the design.
Get Me An Architect!
The first step toward a good design is the system architecture. Knowing the parts that make up your complete system and laying them out on a board using computer-aided software will help visualize what the board will end up looking like.
Be sure to keep memory, CPU, MCH sections separate from the ICH and IO sections. This will help create a clean design. This first step ensures that the designer will have a plan to work with when doing schematics and layout of devices. Figure 1 shows a sample board which employs a clean design technique.
Figure 1. Sample Customer Board with a clean design
Figure 1 illustrates a design that employs a good architecture and layout method by following the product PDG.
It is important to check the schematics against the guidelines provided for various high-speed buses (Clock signals, DDR2, DDR3, PCI Express, etc.) and to correct the errors. It's also imperative that all the pull-up/pull-down resistors are verified for the value and the voltages provided to the devices are checked. Additional information on schematic design and the process of checking schematics is available in the Embedded Design Center (EDC).
Schematics need to be thoroughly checked since layout is directly cascaded down from the schematics. A small error in the schematic will be harder to find in layout. Layout engineers do not check for the right values; they layout the schematic reports.
What's with the "Layout"?
High-speed signal principles are put to use in the layout stage. This stage defines how the copper wires on the PCB are cut into traces of stripline and microstrip. All the devices are also placed on the board either on the top or bottom layer and interconnections are made through an intensely woven inner layer of signals.
Layout is another stage during the design where the principles play a vital role. Most of the principles can be followed in a general manner in the architecture and schematic steps, but during layout the high-speed design principles are used in every signal route.