PPKE ITK PhD and MPhil Thesis Classes

16 1. INTRODUCTION
apply an adequate voltage to change the structure of the crystal into a low resistance
polycrystalline silicon-metal alloy. The transformation could not turned
back and that is why it can be programmed only once. This technology is applied
by Actel [35] and QuickLogic [36].
There are several memory based interconnection structure, which are commonly
used by the larger FPGA manufacturers. The main advantage of these
structures over the antifuse solution is the reprogrammability. This property
gives the chance to the architecture designers to make rapid development of the
architectures cost efficiently. The SRAM-based technology for FPGA configuration
is commonly used by Xilinx [37] and Altera [38]. It contains 6 transistors,
which stores the state of the interconnection. It has a great reliability and stores
its value until the power is turned off.
Three kind of basic building blocks are used in the structure of the programmable
interconnections: multiplexor, pass transistor and tri-state buffer (see
Figure 1.7).
Figure 1.7: Basic programmable switches
Usually multiplexers and pass transistors are used for the interconnections
of the internal logical elements and all of the above are used for the external
routing. (The use of the two, eight or more input multiplexer – depending on the
complexity of the interconnections – is popular among the FPGAs.) The reason
of the wiring inside of a logical cluster is follows:
• implementation of low delay interconnections between the elements of the
clusters,