Second-generation XCITE technology provides controlled impedance drivers and on-chip termination for single-ended and differential I/Os for Virtex-II Pro Platform FPGAs.

Today’s high-performance chips with fast signal rates require termination to prevent signal reflections and to maintain signal integrity. Historically, engineers have used external termination resistors. However, with advanced packaging technologies and availability of hundreds of I/Os, external termination resistors are no longer viable, especially for ball grid array packages.

To solve this problem, Xilinx pioneered adaptive on-chip termination with XCITE (Xilinx Controlled Impedance Technology) in Virtex™-II Platform FPGAs. XCITE dynamically eliminates drive strength variation due to process, temperature, and voltage fluctuations. XCITE uses two external high-precision resistors per I/O bank to incorporate equivalent input and output impedance internally for hundreds of I/O pins. Not only is the cost of the resistors saved (and the additional manufacturing costs that accrue with them), but with fewer printed circuit board respins the cost of developing PC boards also decreases, as illustrated in Figure 1.

Increase Signal Integrity

With XCITE, you can eliminate hundreds of external resistors and increase the signal integrity of your boards for single-ended connectivity solutions such as low-voltage complementary metal-oxide semiconductors (LVCMOS). With higher performance I/O becoming more pervasive, you need this capability not only in single-ended connectivity, but in differential signals as well.

Now, Xilinx offers second-generation XCITE technology in the Virtex-II Pro™ Platform FPGA family, extending to popular connectivity standards like low-voltage differential signaling (LVDS), as shown in Figure 2.

Second Generation XCITE Technology

Second-generation XCITE for Virtex-II Pro FPGAs provides controlled imped-ance drivers and on-chip termination for single-ended and differential I/Os.

XCITE can be used on any I/O block in any bank, thus offering absolute flexibility and independent operability on each I/O bank. When applied to inputs, XCITE provides controlled impedance input parallel termination.

When applied to outputs, XCITE provides controlled impedance series as well as parallel termination. Each of the eight Virtex-II Pro I/O banks supports XCITE, controlled by just two external reference resistors per bank.

Conclusion

As shown in Table 1, Virtex-II Pro Platform FPGAs offer second-generation XCITE technology that gives you increased signal integrity for both single-ended and differential signaling. Using XCITE technology allows you to dramatically reduce the number of resistors to lower your component costs. The increased signal integrity of each Virtex-II Pro Platform FPGA design reduces the risk of board redesign, delivering even more cost reduction. Simplify your designs and lower your costs with Virtex-II Pro FPGAs with XCITE. For more information, go to www.xilinx.com/xcite/.

Second-Generation Technology	Proved in the field and used extensively by customers means you can rest assured about its functionality – another Xilinx innovation for lowering risk, improving design efficiency, and maximizing performance.
Lower Costs	By using XCITE, you need fewer resistors, fewer PCB traces, and less board real estate – all resulting in lower PCB costs.
Absolute I/O Flexibility	Use any termination on any I/O bank. Non-XCITE technology alternatives deliver limited functionality with compromising banking restrictions. XCITE input buffers support full and half impedance.
Support for Popular Standards	Wide support for many I/O standards, including LVDS, LVDSEXT, LVCMOS, LVTTL, SSTL, HSTL, GTL, and GTLP.
Maximum I/O Bandwidth	With less ringing and reflections, you can maximize your I/O bandwidth.
Immune to Temperature and Voltage Changes	Temperature and voltage variations lead to significant impedance mismatches. XCITE provides complete immunity by dynamically adjusting on-chip termination with digitally controlled impedance at all temperatures and voltages.
Eliminates Stub Reflection	XCITE technology improves discrete termination techniques by eliminating the distance between the package pin and resistor.
Increased System Reliability	With fewer components on board, XCITE delivers higher reliability.

Table 1 - XCITE benefits for Virtex-II Pro Platform FPGAs

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