FPGA Architecture
Introduction
The full form of FPGA is “Field
Programmable Gate Array”. It contains ten thousand to more than a million logic
gates with programmable interconnection. Programmable interconnections are
available for users or designers to perform given functions easily. A typical
model FPGA chip is shown in the given figure. There are I/O blocks, which are
designed and numbered according to function. For each module of logic level
composition, there are CLB’s (Configurable Logic Blocks).
CLB performs the logic operation given
to the module. The inter connection between CLB and I/O blocks are made with
the help of horizontal routing channels, vertical routing channels and PSM
(Programmable Multiplexers).
The number of CLB it contains only
decides the complexity of FPGA. The functionality of CLB’s and PSM are designed
by VHDL or any other hardware descriptive language. After programming, CLB and
PSM are placed on chip and connected with each other with routing channels.
The general FPGA architecture
consists of three types of modules. They are I/O blocks or Pads, Switch Matrix/
Interconnection Wires and Configurable logic blocks (CLB). The basic FPGA
architecture has two dimensional arrays of logic blocks with a means for a user
to arrange the interconnection between the logic blocks. The functions of an
FPGA architecture module are discussed below:
• CLB (Configurable Logic Block)
includes digital logic, inputs, outputs. It implements the user logic.
• Interconnects provide direction
between the logic blocks to implement the user logic.
• Depending on the logic, switch
matrix provides switching between interconnects.
• I/O Pads used for the outside
world to communicate with different applications.
Advantages
It requires very small time;
starting from design process to functional chip.
No physical manufacturing steps are
involved in it.
The only disadvantage is, it is
costly than other styles.
Importance
of FPGA
FPGA hold promise of delivering
even in harsh conditions. The cyclone devices from Altera work well in
temperature ranges of -40 degrees to 85 degrees. Another factor that promotes
their long term use is the long term availability. ASIC manufacturers do not
agree on availability of 5 or at maximum 10 years, where as FPGAs have nearly
unlimited availability even if device migrates to next generation.
These find use in microprocessor
systems like the PowerPC405 embedded cores, in Digital Signal Processing as
embedded multipliers and in I/O Processing like Digitally controlled Impedance.
It is always better to be sure of the design and its performance by testing it
on FPGA’s before going in for ASIC circuits. These are employed in Defense
systems and medical imaging. The possibility of evolvable hardware was revealed
while implementing speech recognition on an FPGA using genetic
algorithm. FPGAs being parallel processing devices find use in applications
like brute force attacks used in breaking cryptographic algorithms, in
convolution and FFT computations.
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