What is a system:

System integrities include signal integrity (SI), power integrity (PI) and electro-magnetic compatibilities (EMC) in general. They are analyzed via circuit modeling and simulations. However, what is the scope of a system?

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Fig.1 is a typical pc mainboard we usually see. There are many components, such as heat sinks, various capacitors and connectors on the board’s top layer. When flipped over, we also see that there are many solder points and routing traces like Fig. 2. System like this is the scope of our analysis. Note that it doesn’t have to be a PC system… mobile phone, embedded devices or even high-end server are also treated the same. They are just different in terms of circuit size and scale.

 

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These systems are designed with CAD software (Fig. 3) When we zoom in part of the schematic, we will find many routing traces extended from the chip’s pins’ locations to the edge of the board… usually where the connectors are located. (Fig. 4)

 

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If we further zoom in to the edges around these chip’s pins, and visually in a 3D view (Fig. 5), One may see that there are many vertical cylinders making transitions between different layers. As a package and sometimes sockets sit between silicon chip and underlying mainboard, and a system board is also mostly composed of more than top and bottom layers. These cylinders are called “Via”. A cross-section view makes these via transitions more clear. Conducting traces are extended outwards like roads carrying electrons leaving the central hub.

 

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Moving upstream toward inside the chip, we will be marching into the silicon world where designs are mostly realized with MOSFETs. Logics are computed and bits/bytes are stored here. Signals are eventually buffered and amplified before sending out to pass through aforementioned vias, traces, capacitors, connectors and finally reach the end of path.. receiver.

 

System Modeling:

From these simple illustrations above, one can see that in order to analyze a system’s performance, the following involved factors must be studied and modeled for simulation:

  • Driver/Receiver: How to create and simulate transistor buffers. Topics include IBIS and AMS modeling etc.
  • Packaging: Type of packaging and how to model etc.
  • PC board: How to model and analyze different layer stack-ups. How does the dielectric medium and conductors affect the signaling etc.
  • Trace (Transmission line): how to plan, model and analyze their cross talks etc.
  • Via/Connector: How to create such model, and analyze their performance.
  • Channel: How to assemble the individual elements above together as a channel and perform circuit analysis.
  • Signal: Signal for different interfaces (PCIe, DDR etc), signaling (single-ended and differential) and encoding etc.

In the subsequent topics, we plan to walk through the modeling and analysis practices for these system elements.

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