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LVDS Comparison: APEX 20KE vs. Virtex-E Devices

APEX 20KE devices offer a True-LVDS solution with data transfer rates up to 840 Mbps. Embedded dedicated circuitry enables the True-LVDS solution to deliver high performance and high-quality signals. Virtex-E devices have emulated the LVDS I/O interface using device resources such as configurable logic blocks (CLBs), block RAM, and on-board components such as external resistor packs. LVDS emulation in Virtex-E devices leads to degraded performance and poor signal quality.

Comparing APEX 20KE & Virtex-E LVDS Driver Quality

The quality of output drivers is typically measured using an "eye diagram," which is a superimposition of signal transitions over a period of time. Figures 1 and 2 below compare the outputs of APEX 20KE and Virtex-E LVDS drivers. The results were obtained in the lab using EP20K400EFC672-1X and XCV2000E-8BG560C devices, respectively. For details of how an eye diagram is formed, see the Formation of an Eye Diagram page.

Figure 1. APEX 20KE LVDS Eye Diagram

Figure 1. APEX 20KE LVDS Eye Diagram

Figure 2. Virtex-E LVDS Eye Diagram

Figure 2. Virtex-E LVDS Eye Diagram

The APEX Advantage

The APEX True-LVDS solution provides the following advantages over the Virtex-E emulated LVDS solution:

  • 5x longer data valid time
  • 67% less jitter

A longer data-valid time and less jitter means APEX 20KE devices present a more robust and easy-to-use solution.

Table 1. APEX 20KE True-LVDS vs. Virtex-E LVDS features
Feature APEX 20KE Virtex-E APEX Advantage
Maximum LVDS data rate 840 Mbps 622 Mbps Higher data transfer rate
Dedicated transmitter and receiver circuitry Check   High performance
On-chip (phase-locked loops) PLLs for 8x multiplication Check   Easy board design
True differential drivers Check   Superior LVDS interface
Dedicated power and ground pins Check   Limited ground bounce

Conclusion

Altera APEX 20KE devices provide a superior LVDS solution compared to the Virtex-E devices. The eye diagrams show that the APEX 20KE LVDS drivers generate higher quality signals than the Virtex-E emulation. Dedicated serializer and deserializer circuitry, on-chip 8x PLL, and dedicated LVDS drivers make the APEX 20KE True-LVDS solution the most robust LVDS solution in programmable logic devices.

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