Programmable Logic Devices (PLD)
Programmable Logic Devices (PLD)
PLD chips can be erased electrically and program to implement
different logic function.Designing with PLD chips is faster which
reduce time to bring the product in market.To reprogram PLD we do
not have to redesign circuit board.Simple Programmable Logic
Devices (SPLD), Complex Programmable Logic Devices (CPLD) and Field
Programmable Gate Array (FPGA) are the types of Programmable Logic
Devices (PLD).SPLD includes Read Only Memory (ROM), Programmable
Logic Array (PLA), Programmable Array Logic (PAL) and Generic Array
Logic (GAL).FPGA and CLPD are the types of advanced PLDs.
Simple Programmable Logic Devices (SPLD)
There are three main types of SPLD architecture Programmable
Logic Array (PLA), Programmable Array Logic (PAL) and Generic Array
Logic (GAL).SPLD is made from macro cell each cell made from AND-OR
structure based on the AND array feeding into OR array.PLA have
four input and four output.PLA can not be reconfigured.PLA is One
Time Programmable (OTP).PAL is simpler than PLA architecture.PAL
have faster designing.PAL have have 20 to 24 pins.PAL have low
propagation delay of about 5 ns.PAL is One Time Programmable
(OTP).PAL can not be reconfigured.GAL uses EEPROM configuration so
it can be reconfigured.
Complex Programmable Logic Devices (CPLD)
CPLDs are the collection of SPLD structures which are
interconnected via multiplexer or switch matrix.CPLD consists of
number of logic blocks or functional blocks.And each block contain
PLA or PAL.Using CPLDs more complex design can be
implemented.Propagation delay is about 8 ns.CPLD have large number
of gates and can include complicated feedback path.CPLD are ideal
for critical control application because it offers predictable
timing characteristics.CPLD are use in cost sensitive application
and it have low power usage.
Field Programmable Gate Array (FPGA)
FPGA is field programmable gate array.FPGA are PLDs which are
made from interconnected small macro cells.It is made from logic
cells.Logic cells are connected each other by horizontal and
vertical channel.Each logical cell is having a complicated
design.These logic gates are made from NAND gates.They are
thousands in number.You can make anything using FPGA like you can
make it a microcontroller or you can make it digital signal
processor or any thing.FPGA consist of various I/o pins.
I/o pins connects the chip to the outside world.All the logic
gates are connected to each other via channel these channel are
made from conducting metal.The channels are matrix in shape.With
FPGA it is possible to integrate multiple storage registers,
arithmetic and logic circuits, controllers etc. on the same
device.FPGA is a very flexible chip.FPGA is a volatile device.It
clear everything when the power supply is removed.FPGA have 84 to
256 pins.
WHAT ARE FPGAs USES ?
FPGA is use for High Performance Computing.FPGA is use for
Digital Signal Processing (DSP).FPGA is use for Phase-locked
loops.FPGA is use for Routers.FPGA is use for Video & Image
Processing.FPGA is use for High-end RADARs.FPGA is use for Speech
recognition.FPGA is use for ACSI prototyping.FPGA is use for
Bioinformatics.
WHAT ARE FPGAs ADVANTAGES ?
Make anything like DSP or Microcontroller.It is too
fast.Programmable.Shortertime to market.FPGA are suitable choice
for microprocessor.Efficient system.Parallel data processing.Update
feature from customer site.Real time applications.Synthesis is
easier than ASCI.
WHAT ARE FPGAs DISADVANTAGES ?
Its cost is very high.Not optimize for power consumption.It is
very complicated.Programming is difficult.Volatile.Large number of
pins.Slow design software.Don't provide fix delay.
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