ĐIỆN tử VIỄN THÔNG near field communication khotailieu

 The design includes a near-field transmitter and receiver to send data from one computer to another... Modulation/Demodulation Scheme  Frequency Shift Keying FSK  VCO produces a fr

Near-Field Communication

Group #31

Keshav BansalDan Hvala

 NFC is a short-range wireless

technology.

 NFC provides unique advantages

over other available wireless

technologies

 The design includes a near-field

transmitter and receiver to send

data from one computer to another

Benefits & Features

communicate with each other using the same frequency

Modulation/Demodulation

Scheme

 Frequency Shift Keying (FSK)

 VCO produces a frequency-modulated signal at the transmitter

 Phase lock loop demodulates the

signal at the receiver.

System Overview

Pictures

System Overview

(Schematic)

PC Interface

(Schematic)

MAX232A Input/Output

Voltage Controlled

Oscillator

 Operates on a 12-V power supply

 Accepts an input from 3.7V to 4.2V from the PC interface

 Outputs a signal whose frequency varies according to the input

voltage level

VCO Output

Power Amplifier

 Accepts an input from the VCO

 Outputs the signal to the loop

antenna

 Power gain of approximately 11dB

Power Amplifier

(Schematic)

Vout

Amplifier Input/Output

Loop Antenna

 Very directional

 Larger loop = more gain

 Picks up less noise

 Small, multi-loop turn does not radiate much

Frequency Comparisons

Phase Lock Loop

 Tracks the frequency and phase of the input

 Frequency of an FSK signal

changes according to the data bits; therefore, PLL can demodulate an FSK signal

 Output is the VCO control voltage

Phase Lock Loop

(Block Diagram)

Phase Lock Loop Tracking

 Small antenna bandwidth made us

to revise our original design

 Drift in the frequency of VCO

 Amplifier oscillation

 Most significant bit flipping

Future Hardware

Development

 Less power consumption

 More efficient loop antenna for larger range

 Smaller setup

 Two-way communication

 Strengths

 No interference due to decaying fields

 Within FCC regulation

 FCC requires max E-field of 334uV/m at 30m

 Our max E-field at 30m is 180uV/m

 Weaknesses

 Very small range

 Sensitive to distance and alignment

 653mW

 Maximum bit rate of 800kbps

 Text communication between two PCs

 Transmission range of 30cm

 Ability to send a text file between