7.4 THE MPGA AS AN ALTERNATIVE TO THE FPGA FOR LOW-VOLUME PRODUCTION
The mask-programmable gate array (MPGA) is a well-established alternative to the FPGA for designs that go into production, assuming sufficient quantities are required. Consideration of time-to-market strategy affects the choice between MPGA and FPGA technology [Xilinx92].
As discussed in Chapter 1, MPGAs are arrays of transistors that are configured into the logic required by metal interconnections made in the final stages of fabrication. Partially completed wafers can be stockpiled, ready to be customized for a particular design that takes three weeks or less, compared with 16 to 18 weeks for the full-custom process, assuming a couple of design and fabrication iterations. MPGAs are available in a range of sizes and may have more than 100,000 gates, with typical utilization figures of 80–90% for small arrays and 40–60% for the largest. There are approximately 24,000 gate array designs initiated each year worldwide, and the annual volume in 1990 was reaching $3.5 billion. Nearly half the designs require 10,000 or fewer gates, and consequently FPGAs offer an alternative in many cases.
An MPGA design will typically occupy about one-third the area of an equivalent FPGA design since it does not require configuration storage. In consequence, volume quantities (5000 plus) tend to be cheaper than for the FPGA. At the same time, there are certain fixed costs in producing the MPGA design, referred to as NRE charges, which ...