VHDL FPGA Applications

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VHDL/FPGA Applications inSignal Processing andCommunications

By: Robert Patterson and Ismail Jouny

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Overview of Presentation

n Description of an FPGA

n Description of VHDL

n Applications– Error Control Coding

– CDMA Communications

– Master/Slave And Token Ring Networks

– Pattern Classification With A Hopfield NeuralNet

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Design Options

n TTL logic chips– Difficult for large designs

– Customized board

n PLD– Limited by power consumption and time delay

n ASIC/MPGA– Custom masks required for wiring

– Expensive

– Long turnaround time

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What is an FPGA?

n Field Programmable Gate Array

n Consists of:n An array of configurable logic blocks

n Programmable I/O blocks

n Programmable interconnects

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Benefits of Using an FPGA

n Programmed by users at their site usingprogramming hardware

n Can implement tens of thousands of gates oflogic on a single IC

n Can be programmed many times

n Short development time

n Low cost

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What is VHDL?

n VHSIC Hardware Definition Language

n Common Language for Designers (> 50%)

n High-Level Language

n Simulation and Synthesis Tools areAvailable

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Error Control System Overview

A/D converter

Encoder

Introduction of Error

Decoder

D/A converter

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Error Control Coding Overview

n By adding redundancy in the signal, errorscan be detected and corrected

n Signals are broken up into blocks of data

n Parity calculations add extra bits to signal

n Receiver tries to detect and correct the errorthrough the use of the parity bits

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(7,4) Hamming Code

n 4 data bits => 7-bit code word

n Minimum distance between codes is 3

n All single bit errors can be corrected

- or -

n All single and double bit errors can bedetected

A B

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What is CDMA?

n Code Division Multiple Access

n Multiple users can use a wide slice of thebandwidth

n A unique code accesses the user’sinformation

n Codes are made orthogonal as much aspossible to reduce cross correlation

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CDMA Design Overview

Encoder

Encoder

Pn1

Pn2

Decoder

Decoder

Pn1

Pn2

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Spectrum Spreading

n Data signal

n PN-code

n Coded signal

Received signal at Decoder #1 = (M1•Pn1 + M2•Pn2)•Pn1

= M1•Pn1•Pn1 + M2•Pn1•Pn2

= M1 + M2•Pn1•Pn2

= M1

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Master/Slave Network Overview

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Token Ring Network Overview

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Hopfield Neural Net

n An artificial network that is capable ofrecalling certain stored patterns from a setof inputs

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Hopfield Neural Net (cont.)

n The weight matrix is formed fromexemplars

∑

≤≤

≠

1-N j ,i 0 j , = i ,0

j i xx = t

, sj

si

1-M

0 = sij

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Problems Encountered

n VHDL à Synthesis/Implementation

n Memory in FPGA

n Speed of computer in the synthesis ofdesign

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Conclusions

n VHDL/FPGA combination is a verypowerful design tool– Versatile

– Adaptable

– Efficient

– Economic