1. Near-Field Communication
Group #31
Keshav Bansal
Dan Hvala
Tyler Rossi

2. Introduction
 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

3. Benefits & Features
 Not restricted to 1-to-1 communication
 Multiple devices in a small area can
communicate with each other using the
same frequency.
 Maximum transfer bit rate of 800kbps.
 No special software is required.
 Operation at a frequency of 13.5 MHz
 No ethical concerns due to range

4. 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.

5. System Overview
 Hardware
 Transmitter
 PC interface (MAX232A)
 Voltage-Controlled Oscillator (POS+25)
 Power Amplifier (LM6181)
 Loop Antenna
 Receiver
 Loop Antenna
 Amplifier (LM6181)
 Phase Lock Loop (NE564)
 PC interface (MAX232A)

6. System Overview

7. Pictures

8. System Overview
(Schematic)
VCC
0.1uF
0.1uF
1 0.22uF
0.22uF
6 Antenna 5 10K
1 16
2 C1+ MAX232A VCC V
7 10K
3 2 15 180 180
V+ Gnd
8 0.1uF
3 14 1
4 C1- V+ 300pF 1 TTL
9 T1 Out V+ NE564 Output 6
Loop 1 1.2K
5 4 13 V+ 2 Gain Hysteresis
C2+ R1 In
HA17741 set
5
0.1uF Control 1 2K
5 12 300pF 3 Analogue
Serial Port C2- R1 Out
50 Ω Ω
50 Input
Out
4
V- V- 4 13 10uF
6 11 50 Ω 1K Loop Filter Set Cap
V- T1 In
2K 1
7 10 5 33pF
0.1uF
T2 Out T2 In 820 Ω 820 Ω Loop Filter Set Cap 2
6 VCO 11
8 9 180 FM/RF Input Out
R2 In R2 Out
0.1uF 1K 7 10
180 Bias Filter V+ 510
220 VCO
0.1uF 8 9
Ground Out 5
3.7V TTL 510 V
VCC
0.1uF
0.1uF
Antenna
1 V 8 1
VCC POSTune 1
-25 MAX232A VCC 6
C1+
2 RF 7 LM6181 1
VCOGND 2 1
Out V+ V+ Gnd 5
0.1uF 1 6
3 GND GND 6 3 2
C1- T1 Out 4
7
4 5 50 Ω 4 13 3
GND GND 50Ω V- C2+ R1 In
0.1uF 1 8
Ω 5 4
50 C2- R1 Out 2
9
6 V- 11 5
820 Ω 820 Ω T1 In
0.1uF 7 10
T2 Out T2 In
Serial Port
8 9
R2 In R2 Out

9. PC Interface
 Connects through serial cable
 Received by MAX232A
 0 to 5V square wave
 Voltage divider
 Non-inverting voltage adder

10. PC Interface
(Schematic)
VCC
0.1uF
0.1uF
1
6 1 16
2 C1+ MAX232A VCC
7
3 2 15 180 180
V+ Gnd
8 0.1uF
4 3 14
C1- T1 Out V+
9
5 4 13
C2+ R1 In
HA17741
0.1uF
Serial Port 5 12
C2- R1 Out
V-
6 11
V- T1 In
2K
0.1uF 7 10
T2 Out T2 In
8 9 180
R2 In R2 Out
180
220
3.7V
Antenna
1 V 8
VCC POSTune
-25
2 RF 7 LM6181
Out
VCOGND V+
3 GND GND 6

11. MAX232A Input/Output

12. 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

13. VCO Output

14. Power Amplifier
 Accepts an input from the VCO
 Outputs the signal to the loop antenna
 Power gain of approximately 11dB

15. Power Amplifier
(Schematic)
0.22uF
Antenna 5
V
10K
300pF 1
V+ N
Loop
V+ 2 Gain
Control
3
Vout
300pF
50 Ω 50 Ω Input
V- 4
Ω
50 1K Loop Filt
5
820 Ω 820 Ω Loop Filte
6 FM/RF In
0.1uF 1K 7
Bias Filte
Vin 0.1uF 8
Ground
VCC
0.1uF

16. Amplifier Input/Output

17. Loop Antenna
 Loop Diameter = 6.5 cm
 Inductance = 3 uH
 Capacitor used to resonate the antenna
at 13.5 MHz = 45 pF

18. Loop Antenna
 Very directional
 Larger loop = more gain
 Picks up less noise
 Small, multi-loop turn does not radiate
much

19. Frequency Comparisons

20. 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.

21. Phase Lock Loop
(Block Diagram)

22. Phase Lock Loop Tracking

23. Band-Pass Filters
(Eliminated)
 Tuned to 10MHz and 13.5MHz
 Pass-band of 2-3MHz
 Signal did not decay fast enough outside of
the pass-band
+Supply
+
Vout
-
Vin
-Supply

24. Difficulties
 Small antenna bandwidth made us to
revise our original design.
 Drift in the frequency of VCO.
 Amplifier oscillation
 Most significant bit flipping

25. Future Hardware Development
 Less power consumption
 More efficient loop antenna for larger
range.
 Smaller setup
 Two-way communication

26. Analysis
 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

27. Results
 Maximum bit rate of 800kbps
 Text communication between two PCs
 Transmission range of 30cm
 Ability to send a text file between PCs

28. Credits
 Ethan Miller
 Dr. Ada Y. Poon
 Dr. Christopher Schmitz
 Dr. Steven Franke
 Workers in the ECE Parts Shop