FPGA INTERCONNECTS

AND PROGRAMMABILIT

Y

Presented by :Srishti Jain (cs - A)

V sem

FPGA :- A Field Programmable Gate Array (FPGA) is a

Programmable Logic Device(PLD) with higher densities and capable of implementing different functions in a short period of time.

Topics covered:-

• FPGA Overview

• FPGA in detail

• Programming Methodology

FPGA overview

2-D array of logic blocks and flip-flops with programmable interconnections.

Compact designUser can configure

Intersections between the logic blocks The function of each block

FPGA in detail:Logic blocks:

has an undefined function at the time of manufacture. before use, it must be programmed (i. e. reconfigured).

Contains- Look-Up-Table(LUT) Multiplexer Flip-flop

Can be programmed to function as Transistor Microprocessor Any combination of combinational and sequential

logic functions

to be continue..

INTER CONNECTIONSAre electrically programmable interconnection

between the logic blocks.

Also contains electrically programmable switches.

A hierarchy of interconnect allows logic blocks to be interconnected as per system designer. Like one chip programmable breadboard.

Programming MethodologyElectrically programmable switches are used to program

FPGAProperties of programmable switch determine on-

resistance, parasitic capacitance, volatility, reprogrammability, size etc.

Desired properties: Minimum area consumption Low on resistance; High off resistance Low parasitic capacitance to the attached wire Reliability in volume production

Various programming techniques are:- SRAM programming technologyAntifuse programming technologyEPROM /EEPROM programming technology

SRAM Programming TechnologyEmploys SRAM (Static RAM)

cells to control pass transistors and/or transmission gates

SRAM cells control the configuration of logic block as well

VolatileNeeds an external storageNeeds a power-on

configuration mechanism In-circuit re-programmable

Lesser configuration time

Occupies relatively larger area

Anti-fuse Programming Technology

Though implementation differ, all anti-fuse programming elements share common propertyUses materials which normally resides in high

impedance stateBut can be fused irreversibly into low impedance

state by applying high voltage

Very low ON Resistance (Faster implementation of circuits)

Limited size of anti-fuse elements; Interconnects occupy relatively lesser areaOffset : Larger transistors needed for

programmingOne Time Programmable

Cannot be re-programmed (Design changes are not possible)

Retain configuration after power off

EPROM Programming Technology

EPROM Programming TechnologyTwo gates: Floating and SelectNormal mode:

No charge on floating gate Transistor behaves as normal n-channel transistor

Floating gate charged by applying high voltage Threshold of transistor (as seen by gate) increases Transistor turned off permanently

Re-programmable by exposing to UV radiation

EPROM transistor

EPROM memory cell

No external storage mechanismRe-programmable (Not all!)Not in-system re-programmableRe-programming is a time consuming taskAn EPROM cell is erased by discharging

the electrons on that cell’s floating gate. The energy required to discharge the

electrons is provided by a source of ultraviolet (UV) radiation.

EEPROM Programming TechnologyTwo gates: Floating and SelectFunctionally equivalent to EPROM;

Construction and structure differElectrically Erasable: Re-programmable

by applying high voltage(No UV radiation expose!)

When un-programmed, the threshold (as seen by select gate) is negative!

summary

Other FPGA Advantages

Manufacturing cycle for ASIC is very costly, lengthy and engages lots of manpower

Mistakes not detected at design time have large impact on development time and cost

FPGAs are perfect for rapid prototyping of digital circuits

Easy upgrades like in case of softwareUnique applications

Why better ?FPGA programmed using electrically

programmable switchesRouting architectures are complex.Logic is implemented using multiple levels of

lower fan-in gates.Shorter time to market Ability to re-program in the field to fix bugs

FPGA DISADVANTAGE FPGAs are generally slower than their

application-specific integrated circuit (ASIC) Can't handle as complex a design, and draw

more power.

Application Reconfigurable computing. Applications of FPGAs include DSP, software-

defined radio. The inherent parallelism of the logic resources

on the FPGA allows for considerable compute throughput.

FPGA Design and ProgrammingTo define the behavior of the FPGA the user provides a

hardware description language (HDL) or a schematic design.

Then, using an electronic design automation tool, a technology-mapped net list is generated.

The netlist can then be fitted to the actual FPGA architecture using a process called place-and-route.

The user will validate the map, place and route results via timing analysis, simulation, and other verification methodologies.

Once the design and validation process is complete, the binary file generated used to configure the FPGA.

THANK YOU