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Introduction to programming
technologies
One of the first technique that allowed users to
program their own devices was- and still is
known as fusible-link technology.
In this case the device manufactured with all
of the links in place, where each link is
referred to as a fuse.
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Fusible Link technologies
A simple programmable function
Every Programmable function is implemented using
Potential links
Pull up resistors
Input and output terminals
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Un programmable fusible links
In Un programmable fusible links uses the fuses aresimilar to the fuses you find in household products like a
television. If anything untoward occurs such that the
television starts consuming too much power its fuse will
burn out.
This results in an open circuit
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Programmable Fusible Links
Here programming is done by selectively removing the
undesired fuses by applying pulses of relatively high voltage
and current to the devices inputs.
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The process of selectively removing the fuses is
known as programming( but it may also referred to as
burning or blowing)
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Drawback
Devices based on the fusible link technologies are
said to be one-time programmable(OTP), because
once a fuse have been blown it cant be and no going
back..
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Antifuse technology
This Antifuse technology is an alternative to the fusible technology
In which each configurable path has an associated link called Antifuse.
In its unprogrammmed state Antifuse has high resistance that is considered
to be an open circuit.
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Programming an antifuse
Antifuses can be selectively grown(programmed) by applying
proper high voltages and currents to the device's inputs
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The Polysilicon via converts insulation to conduction
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These antifuses are also OTP devices
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MASK PROGRAMMABLE DEVICES
Electronic systems in general and computers in particular-
make use of two major classes of memory devices: read-only
memory (ROM) and random-access memory(RAM)
ROM:
1.nonvolatile
.2.Other components in the system can read data from ROMdevices, but they cant write data into them.
RAM:1. Volatile
2.By comparison data can be both written into and read out ofRAM devices which are said to be volatile .
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Basic ROMs are mask programmed
Their construction by means of photo masking.
Photo masking is used to create transistors
and metal tracks
ROM
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The problems of Mask devices
Creating the masks are very expensive
They are useless, unless producing theextremely large quantities
To overcome the above problem theyinvented programmable ROMs
PROM, EPROM,EEP[ROM
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PROM
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Thses are used as memory devices
Used to implement simple logics
Cheap
They designed using fusible and anti
fusible technoilogies
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EPROM
Theses are also called as reprogrammable
devices
Being introduced by Intel in 1971
Its structure is same as standard MOS
transistor but with the addition of second
polysilicon floating gate isolated by layers
of oxide.
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In its unprogrammed state , the floating
gate uncharged and doesnt affect the
normal operation of the control gate.
Inorder to program the transistor , a
relatively high voltage is applied b/w drain
and gate
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This 12V causes the transistor to be truned on
and energetic electrons force their way through
the oxide into the floating gate in a processknown as hot (high enery ) electronic injection.
When the programming signal is removed a
negative charge remains on the floating gate
and it is stable and will not dissipate more than
one decade under normal operations.
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An EPROM is erased by discharging the
electrons on that cells floating gate.
The energy required to discharge the electrons
by a source of ultraviolet (UV) radiation
If the area smaller amd then density increases, alarger percentage of the surface of the die is
covered by metal. This makes it difficult for the
EPROM cells to absorb the UV light and
increase the time.
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EEPROM
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The E2PROM transistor is same as
EPROMtransistor in that it contains a
floating gate , but the insulating oxide
layers surroung this gate are very muchthinner.
The second transistor used to erase the
data.
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FLASH based technologies
A deThe name FLASH was originally
coined to reflect this technologies rapid
erasure times compared to EPROM
It has two types of architectures .
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In the first architecture using a singlefloating gate transistor cell with the samearea as an EPRM and thinner oxide like
layer like EEPROM. SO theses devices can clearing large
portions of the data.
The other architecture uses two-transistorcell similar to EEPROM cell to erase wordby word,.
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SRAM based technology
RAMs are two types
SRAM and DRAM
DRAMs : In the case of DRAMs , each cell isformed from a transistor-capacitor pairthat
consumes very little silicon material .
The dynamic qualifier is used because thecapacitor loses its charge over time, so each cell
must be periodically rechraged periodically to
retain its data.
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The output of the SRAM IS CONTROLED BY A
CONTROL TRANSISTOR
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Dis Advantage:
1. It Uses significant amount of siliconbecause each cell comprises of four to six
transistors 2. When power is removed the configured
data will be lost.
Advantage: Thhey can be programmed quickly and
repeateadly as required.
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