TABLE OF CONTENTS Riser and daughter cards offer several advantages to you as a system designer. They allow you more choice in terms of the placement and location of your PCI Express interfaces. However, you must also account for any riser card or daughter card in the system's electrical and timing budgets. For example, if you intend for your design to interface with a standard add-in card as defined by the CEM Specification, the riser card or daughter card must be included in the host system's loss and jitter budgets, and cannot encroach on the add-in card's budget allowances. The same holds true when interfacing with an ExpressCard Module. Simply put, any riser or daughter card must be considered an extension or part of the host system's interconnect path.
The following section presents two examples of riser cards that exist or could be used with either add-in card or ExpressCard modules. For more information, especially pertaining to ExpressCard designs, refer to the ExpressCard Implementation Guidelines (PCMCIA 2003c).
Extension risers are perhaps the simplest form of riser card to implement. They are completely passive in that they don't contain any additional active devices. The extension risers simply extend all the signals coming through a standard PCI Express connector, including power and auxiliary signals, and route them to an additional connector located some length away on the riser card. Figure 5.11 presents a conceptual illustration of this design.
