During FPGA selection, carefully consider the process technology, which helps you identify the leakage and performance of the device. The Xilinx® 7 series FPGAs are based on the 28 HPL (28-nanometer High-Performance, Low-Power) process, covering the high-performance space while also enabling significant power reduction (see cover story, Xcell Journal Issue 76). Choosing devices built on the lower-leakage HPL process eliminates the need for complex and expensive static-power-management schemes in an FPGA design.
FPGAs built with the 28 HP process have no performance advantage over 7 series FPGAs, while some other, competing FPGAs come with the severe penalty of more than twice the static power and present challenges in reducing leakage. Figure 2 shows a holistic power reduction approach for the 7 series family, which has half the overall power consumption of prior-generation, 40-nm FPGA devices.
Figure 2 – Xilinx 7 series FPGAs consume half the power of devices built in the earlier 40-nm process.
Designers can choose a larger FPGA for purposes of development and later migrate to a smaller one in their production line. Choosing a smaller FPGA will not only bring down the cost but will also reduce the power consumption of the system.
All 7 series FPGAs are based on a unified architecture. This unified architecture enables easy upward and downward migration across different FPGA devices and families in the Xilinx 7 series portfolio. Refer to the “7 Series Migration Guide” (UG429) when considering design migration from Virtex®-6 or Spartan®-6 devices to or between 7 series device families.
XILINX STACKED-SILICON INTERCONNECT TECHNOLOGY
For larger systems, designers often choose multiple FPGAs. This type of architecture frequently requires the delicate and difficult task of moving data at rather high speeds among the various FPGAs. Choosing the larger 7 series FPGAs, such as the XC7V1500T and XC7V2000T devices, which are created using Xilinx stacked-silicon interconnect technology, can circumvent this issue. Simply stated, this SSI technology uses multiple dice residing on a silicon interposer that provides tens of thousands of connections among them, to create a single large device. One benefit of stacked-silicon interconnect technology is the reduction in maximum static power compared with a similar-size device on a standard monolithic die.
Stacked-silicon interconnect technology also provides a significant reduction in I/O interconnect power. Compared with having multiple FPGAs on a board, SSI technology boasts a reduction of I/O interconnect power by 100x (bandwidth/W) over an equivalent interface built with I/Os and transceivers. This dramatic reduction is due to all connections being built on-chip rather than having the power required to drive the signals off chip, enabling incredibly high speed and low power.
Table 1 – Static, dynamic and performance power comparisons