A8 Advanced Digital Logic, FPGAs and HDL

Topic

FPGAs are reconfigurable integrated circuits that come from the factory containing a vast number of programmable logic blocks—built, fundamentally, using the same Boolean algebra described by the digital electronics model—along with memory elements and embedded memory blocks, all of which can be interconnected programmably. They allow for the hardware implementation of virtually any desired digital function after the chip has been manufactured, as well as reconfiguration if necessary. The design of these circuits is described using specialized hardware description languages, which enable the specification of the circuit's desired behavior in text form prior to its synthesis onto the physical chip.

A key technique in high-performance digital systems is pipelining: breaking a complex operation down into several simpler stages that execute in a staggered fashion. Although each individual operation takes more clock cycles to complete—resulting in higher latency—the system as a whole can initiate a new operation during every clock cycle, thereby maximizing the number of operations completed per unit of time. The various available memory technologies represent different trade-offs regarding speed, density, cost, and whether or not data is retained when power is lost.

Application-Specific Integrated Circuits (ASICs)—designed and manufactured to perform a single, specific function—are far more efficient in terms of area and power consumption than an FPGA programmed to perform the same task; however, their design and manufacturing entail a much higher initial investment, which is justified only for high-volume production runs.

Thus, this module—which begins by introducing logic blocks that remain reconfigurable after chip fabrication—concludes by demonstrating that this very flexibility comes with a cost that ASICs avoid and offers an advantage that ASICs lack: choosing between the two means deciding whether production volume justifies giving up the ability to change one's design after the chip has been manufactured.

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