FPGA vendors offer a wide variety of packaging, speed, and qualification (military, industrial, or commercial) options in each family. For example, there are several hundred possible part combinations for the Xilinx LCA series. Figure 4.8 shows the Xilinx part-naming convention, which is similar to that used by other FPGA vendors.
Table 4.2 shows the various codes used by manufacturers in their FPGA part numbers. Not all possible part combinations are available, not all packaging combinations are available, and not all I/O options are available in all packages. For example, it is quite common for an FPGA vendor to offer a chip that has more I/O cells than pins on the package. This allows the use of cheaper plastic packages without having to produce separate chip designs for each different package. Thus a customer can buy an Actel A1020 that has 69 I/O cells in an inexpensive 44-pin PLCC package but uses only 34 pins for I/O—the other 10 (= 44 – 34) pins are required for programming and power: three for GND, four for VDD, one for MODE (a pin that controls four other multifunction pins), and one for VPP (the programming voltage). A designer who needs all 69 I/Os can buy the A1020 in a bigger package. Tables in the FPGA manufacturers’ data books show the availability, and these matrices change constantly.
Asking “How much do FPGAs cost?” is rather like asking “How much does a car cost?” Prices of cars are published, but pricing schemes used by semiconductor manufactures are closely guarded secrets. Many FPGA companies use a pricing strategy based on a cost model that uses a series of multipliers or adders for each part option to calculate the suggested price for their distributors. Although the FPGA companies will not divulge their methods, it is possible to reverse engineer these factors to create a pricing matrix.
This range of options gave a total of 600 possible XC3000 products, of which 127 were actually available from Xilinx, each with a different part code. If a designer is uncertain as to exact size, speed, or package required, then they might easily need price information on several dozen different part numbers. Distributors know the price information—it is given to each distributor by the FPGA vendors. Sometimes the distributors are reluctant to give pricing information out—for the same reason car salespeople do not always like to advertise the pricing scheme for cars. However, pricing of the components of a microelectronics system is a vital factor in making decisions such as whether to use FPGAs or some alternative technology. Designers would like to know how FPGAs are priced and how prices may change.
Table 4.3 shows the prices of the least-expensive version of the Actel ACT 1 and ACT 2 FPGA families, the base prices , in the first half of 1992 (1H92). Table 4.4 shows the 1H92 base prices for the Xilinx XC3000 FPGA family. Current FPGA prices are much lower. As an example, the least-expensive XC3000 part, the XC3020A-7PC68C, was $13.75 in 1996—nearly half the 1992 price.
Using historical prices helps prevent accusations of bias or distortion, but still realistically illustrates the pricing schemes that are used. We shall use these base prices to illustrate how to estimate the sticker price of an FPGA by adding options—as we might for a car. To estimate the price of any part, multiply the base prices by the adjustment factors (shown in Table 4.5 for the Actel parts).
The adjustment factors in Table 4.5 were calculated by taking averages across a matrix of prices. Not all combinations of product types are available (for example, there was no military version of an A1280-1 in 1H92). The dependence of price over time is especially variable. An example price calculation for an Actel part is shown in Table 4.6 . Many FPGA vendors use similar pricing models.
Some distributors now include FPGA prices and availability online (for example, Marshall at http://marshall.com for Xilinx parts) so that is possible to complete an up-to-date analysis at any time. Most distributors carry only one FPGA vendor; not all of the distributors publish prices; and not all FPGA vendors sell through distributors. Currently Hamilton-Avnet, at http://www.hh.avnet.com , carries Xilinx; and Wyle, at http://www.wyle.com , carries Actel and Altera.
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