the role of smart wireless communications in advancing ... · ©2005 microchip technology...

© 2005 Microchip Technology Incorporated. All Rights Reserved. Slide 1

The Role of Smart Wireless Communications in Advancing

Automotive Security Applications

Youbok Lee, Ph.D.James B. Nolan

Microchip Technology Inc.2355 West Chandler Blvd.

Chandler, AZ 85224 USA

© 2005 Microchip Technology Incorporated. All Rights Reserved. Class Slide 2

1. What is Smart Wireless Communications?2. Application Examples3. Programmable Digital Wake-Up Filter4. Amplitude Sensitivity and Modulation Depth5. Examples: Smart Passive Keyless Entry (PKE)

System Design6. Conclusions7. References

Table of Contents


Example: Keyless Entry Systems(Yesterday and Today)

Encrypted Codes

UHF Receiver

Microcontroller(MCU)

LED

MCU(KEELOQ®)

UHF Transmitter

LED


1. What is Smart Wireless

Communications ?

● Hands-Free Operation (no human interface) ● 100% Reliable and Stand-Alone● Self-Learning and Self-Adaptable


Small Size and Low Cost

Inexpensive Bi-directional Communication

A smart microcontroller (MCU) that has both digital and analog -front-end circuits in a single package.

Use 125 kHz for the base station command, and UHF for the response.

Requirements Solutions

High input sensitivity of the transponder for the base-station command: ~ 3 mVpp

CommunicationDistance: > 2 meters

Requirements and Solutions


Minimum Antenna Directionality

Long Battery Life

Use three orthogonally placed LF antennas on the transponder board.

Use wake-up filter

Requirements Solutions

Work for Noisy Environment

High input modulation depth sensitivity

Requirements and Solutions(Continued)

Data Security Use encryption/decryption algorithms


Example:Smart Passive Keyless Entry (PKE) Systems

(Tomorrow)

Command

(125 KHz)

Response

(UHF)

Response

(125 KHz)

Encrypted Codes

UHF Receiver

LFTransmitter/

Receiver

Mic

roco

ntro

ller

(MC

U)

LED

Smart MCU

UHF Transmitter

LED

X

Y

Z


Circuit Elements to Receive Signals Coming From All Directions

Smart MCU

X

Y

Z

Bx

Bz

By


UHF TXUHF TX(315/434 MHz)(315/434 MHz)

Example: PKE Transponder Configuration

VDD

DataRFEN

LFDATA/SDIO

VDDT

LCX

LCY

VSS

LED

VSST

LCCOM

LCZ

CS

SCLK/ALERT

3 V

3 V

3 V

3 V1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

PIC

16F6

3 9


2. Application Examples2. Application Examples


l Automotiveu Smart Vehicle Access Systemsu Engine Immobilizersu Tire Pressure Monitoring Systems (TPMS)

Smart Transponder Applications


KSmart Transponder

Home Access Parking Lot Entry

Smart PKE Transponder forMultiple-Purpose Applications

125 kHz Command

UHF Response

UHF Response

125 kHz Command

125 kHz Command

UHF Response

Vehicle Access


RF Receiver

MCU

RF Transmitter

TirePressureSensor

Smart MCU LF Initiator

UHF Tire Pressure Data

Tire Pressure Monitoring Systems(TPMS)

125 kHzInitiator Command


3. Programmable Digital

Wake-Up Filter

3. Programmable Digital

Wake-Up Filter


UHF TXUHF TX(315/434 MHz)(315/434 MHz)

Example: PKE Transponder Configuration

VDD

DataRFEN

LFDATA/SDIO

VDDT

LCX

LCY

VSS

LED

VSST

LCCOM

LCZ

CS

SCLK/ALERT

3 V

3 V

3 V

3 V1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

PIC

16F6

3 9


Output Enable Wake-Up Filter

l Purpose for using the Wake-Up Filter► To reduce operating current (for longer battery life):

Keep digital section in a low-current mode (Sleep) until analog section finds a valid input signal.

l How can it be done ?► Transponder is looking for an input signal with a

predefined header (waveform) only. ► Ignore any other inputs that do not come with the

predefined header.

l Purpose for using the Wake-Up Filter► To reduce operating current (for longer battery life):

Keep digital section in a low-current mode (Sleep) until analog section finds a valid input signal.

l How can it be done ?► Transponder is looking for an input signal with a

predefined header (waveform) only. ► Ignore any other inputs that do not come with the

predefined header.


Wake-Up Filter

Gap

Start Bit

AGC

Data FieldDemodulated Output

Input Signal WaveformProgrammable Wake-Up Filter

Data FieldStabilization

Time


Output When Wake-Up Filter Enabled

Input Signal

DemodulatedOutput


No Output if Input Signal does not meet the programmed Wake-Up Filter timing requirement

Input Signal

Output


Output When Wake-Up Filter Disabled

Input Signal

DemodulatedOutput


4. Amplitude Sensitivity

and Modulation Depth

4. Amplitude Sensitivity

and Modulation Depth


RF Pulses in Near Field

τe

Long Decaying Time

In near field, it is very difficult to achieve 100 % modulation depth unless transmitting data with very slow data rate.


Noisy Environment

Noise Level Signal Level

Modulated Level

Signal Level


Definition of Modulation Depth

B (5 mVPP) A (10 mVPP)

Modulation Depth =

A -B

A X 100 %

Pulsed Signal

(Microchip)

Modulation Depth =(Text Book)

A -B

X 100 %A + B

(50 %)

(33 %)


Example: Detection of Amplitude Modulated Inputs (Continued)

100 % Modulation Input Signal vs. Output

25 % Modulation Input Signal vs. Output

Demodulated Output

Input

Input

Demodulated Output


5. Examples:

Smart Passive Keyless

Entry (PKE) System Design

5. Examples:

Smart Passive Keyless

Entry (PKE) System Design


Example: Smart PKE Transponder with Batteryless and Battery Backup Circuits

UHF Transmitter

LCX

VBAT VDD

D1

D4

D3

D2

C1

LCcomRcom

R Lim

UHF Ant

1.8 V -5.5 V

PIC16F639LCY

LCZ

LCCOM

(Optional)


Working System Requirements

● Transponder► LF Antenna(s)► UHF Transmitter► External Battery Back-up Circuit (optional)► Smart MCU and MCU Firmware

● Base Station► LF Transmitter► UHF Receiver► Antenna► MCU and MCU Firmware


Parameters for Bi-Communication Distance

l Transponderè Antenna Tuning and Qè Antenna Orientation (use 3D

antenna)è Receiving Sensitivityè Modulation Depth of Input Signal è Data Rate

l Base Station è Output Powerè Receiving Sensitivity

Distance


Antenna Design

● LF: 125 kHz ► Use LC Resonant Circuit

♦ Antenna Type: Air-Core or Ferrite-Core (1 -10 mH )♦ LC Resonant Frequency = Carrier Frequency of Base Station

♦ Range:< 1 meter for passive tag < 5 meters for active tag

● UHF: 315 -960 MHz► Use Dipole Antenna: Etched on PCB♦ Range

~ 5 meters for passive tag ~ 100 meters for active tag


Magnetic Flux and Induced Antenna Voltage

))(2

( 2/3221

2

22 dSraNIa

dtdNdSB

dtdN

dtdNV o∫ ∫ +

−=•−=Φ

−=µ

απ

µ

cos2

2

1

13

221

o

o

NSQBfdtdIM

dtdI

rSaNN

≈

−≡

−=

N = Number of Turns of CoilS = Surface Area of Receiver Coilf = Frequency, Q = Quality Factor

Where: TX

C

tII o ωsin=

L

Transmitter Antenna

Magnetic Fields

Receiver Coil

I


0

50

100

150

200

250

0 100 200 300 400 500

Distance (Cm)

Ant

enna

Coi

l Vol

tage

(Vpp

)

0

0.005

0.01

0.015

0.02

0.025

0 100 200 300 400 500

Distance (Cm)

Ante

nna

Coil

Volta

ge (V

pp)

Induced Antenna Voltage Over Distance


Example: PIC16F639 TransponderSee

Refe

rence

[2] f

or more

details


Example: PIC16F639 Base StationSee

Refe

rence

[2] f

or more

details


Example: PIC16F639 Base Station (Continued)

See R

efere

nce [2

] for m

ore deta

ils


6. Conclusions6. Conclusions

● Systems can be built with a smart microcontroller

● Reliable Hands-Free OperationsRequire:

■ High LF Input Sensitivity■ Low Power Consumption

■ Smart Bi-directional Communications■ Low System Cost

■ Secure Data Encryption and Decryption

that can provide the solutions forthe above requirements.


7. References

l [1] PIC12F635/16F636/16F639 Data Sheet, Microchip Technology Inc.

l [2] Microchip Application Notes: AN959, TB088, AN710, and AN912, Microchip Technology Inc.

l [3] Introduction to Radio Frequency Design, by W. H. Hayward, Prentice Hall, 1982.

l [4] Wireless Digital Communications: Design and Theory, by Tom McDermott, Tucson Amateur Packet Radio Corporation, 1998.

l [5] Short Range Wireless Communications, by Alan Bensky, LLH Technology Publishing, 2000.


Key Web Sites for RF Design References

l Microchip : www.microchip.coml FCC: www.fcc.govl European Radio Comm Org: www.ero.dkl Euro Telecom Standards Inst.: www.etsi.orgl IEEE: www. ieee.orgl IEEE 802.15.4 Working Group:

http://grouper.ieee.org/group/802/15/index.htmll Home RF: www.homerf.orgl Bluetooth: www.bluetooth.coml Linx: www.linxtechnologies.com

http://www.microchip.com

http://www.fcc.gov

http://www.ero.dk

http://www.etsi.org

http://grouper.ieee.org/group/802/15/index.html

http://www.homerf.org

http://www.bluetooth.com

http://www.linxtechnologies.com


Thank You!Thank You!

The Microchip name and logo, KEELOQ, PIC and The Microchip name and logo, KEELOQ, PIC and PICmicroPICmicro are registered trademarks of Microchip are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. AllTechnology Incorporated in the U.S.A. and other countries. All other trademarks mentioned herein are other trademarks mentioned herein are property of their respective companies. property of their respective companies. ©©2005 2005 MicrochipTechnologyMicrochipTechnology Incorporated. All rights reserved.Incorporated. All rights reserved.

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