1

6/6/2008 1

Getting One Foot Into RF

2

Abstract

A Wireless primer covering some of the fundamental RF concepts,

Guidance on optimizing system design and maximizing range

Frequency bands available for use

RF solutions available from TI and how to interface an MSP430

RF development tools that are available to get your application kick started.

2

2

3

Agenda

• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)

4

ISM/SRD License-Free Frequency Bands

3

5

1000m

HeadsetsPC PeripheralsPDA/Phone

Medical Industrial Tracking Automation Meter Reading

Data Rate (bps)

100k 1M 10M10k1k

Range

100m

10m

1m

IEEE 802.15.4/ZigBee

PC NetworkingHome NetworkingVideo Distribution

Wi-Fi/802.11

Proprietary Low-Power RadioGamingPC PeripheralsAudioMeter ReadingBuilding Mgt.Automotive

UWBWireless USBVideo/audio links

Short Range Wireless

6

Regional Differences

• Europe – ETSI– 433/868 MHz– 2.4 GHz

• USA – FCC– 315/915 MHz– 2.4 GHz

• Japan – ARIB– 426 MHz– 2.4 GHz

• Other National Requirements

4

7

License Free Sub 1 GHz bands

8

ETSI Example

5

9

ETSI Example 2.4 GHz

2400 2483.5

Output power [dBm]

Frequency [MHz]

EN 300 440

EN 300 328

+20.0

+10.0

FHSS 15 non-overlapping Channels or DSSS

Source: IEEE Wireless Communications Dec 06

10

FCC Example (915 MHz and 2.4 GHz)

6

11

Agenda

• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)

12

Transmission MethodSignal System Complexity

Digital Modulation Techniques

AM, FM Scalar Signals

ASK, FSK, QPSKVector Signals

TDMA, CDMATime Variant

Signals

7

13

Transmission Methods: DSSS and FHSS Power

FrequencyDSSS – Direct Sequence Spread Spectrum

FrequencyFHSS – Frequency Hopping Spread Spectrum

Power Narrow Band Transmission

Wide Band Transmission

14

Modulation and Demodulation

• OOK – ON/OFF Keying• ASK – Amplitude Shift Keying• FSK – Frequency Shift Keying• BFSK or 2FSK – Binary FSK• GFSK – Gaussian FSK • QPSK – Quadrature Phase

Shift Keying

8

15

Basic Building Blocks of an RF System• RF-IC

– Transmitter– Receiver– Transceiver– System-on-Chip (SoC);

typically transceiver with integrated microcontroller

• Crystal– Reference frequency for

the LO and the carrier frequency

• Balun– Balanced to unbalanced– Converts a differential

signal to a single-ended signal or vice versa

• Matching• Filter

– Used if needed to pass regulatory requirements / improve selectivity

• Antenna

16

Extending the Range of an RF System

1. Increase the Output power– Add an external Power

Amplifier (PA)2. Increase the sensitivity

– Add an external Low Noise Amplifier (LNA)

3. Increase both output power and sensitivity– Add PA and LNA

4. Use high gain antennas– Regulatory requirements

need to be followed

9

17

Crystal Accuracy

• Compromise between RF performance and crystal cost

Receiver channel filter BW

Frequency offset0-2·X ppm +2·X ppm

Total error of 4·X ppm

18

Balun

• There are different balun implementations – Trade-off: PCB area versus cost

Microstrip delay line

IC balun

Discrete balun

10

19

Why Matching ?

Zs 150 ohmPa 0 dbm 1 mW Available power from source, requiresd matched load.V 1,095445 V Amplitude of unloaded signal source

Plot vector

Energy dis Energy dissepated in load PL [dBm]ZL PL Power iPL Power inΓ RL [dB] TL [dB] VSWR PL Power in load [mW]

Plot index 1 mW dBm x1 mWPL Power in load [mW] 0 0 -9,04 -1,000 0,00 9,04 30,00 0,00

5 0,12 -9,04 -0,935 0,58 9,04 30,00 0,1210 0,23 -6,30 -0,875 1,16 6,30 15,00 0,2315 0,33 -4,81 -0,818 1,74 4,81 10,00 0,3320 0,42 -3,82 -0,765 2,33 3,82 7,50 0,4225 0,49 -3,10 -0,714 2,92 3,10 6,00 0,4930 0,56 -2,55 -0,667 3,52 2,55 5,00 0,5635 0,61 -2,12 -0,622 4,13 2,12 4,29 0,6140 0,66 -1,77 -0,579 4,75 1,77 3,75 0,6645 0,71 -1,49 -0,538 5,38 1,49 3,33 0,7150 0,75 -1,25 -0,500 6,02 1,25 3,00 0,7555 0,79 -1,05 -0,463 6,68 1,05 2,73 0,7960 0,82 -0,88 -0,429 7,36 0,88 2,50 0,8265 0,84 -0,74 -0,395 8,06 0,74 2,31 0,8470 0,87 -0,62 -0,364 8,79 0,62 2,14 0,8775 0,89 -0,51 -0,333 9,54 0,51 2,00 0,8980 0,91 -0,42 -0,304 10,33 0,42 1,88 0,9185 0,92 -0,35 -0,277 11,16 0,35 1,76 0,9290 0,94 -0,28 -0,250 12,04 0,28 1,67 0,9495 0,95 -0,22 -0,224 12,98 0,22 1,58 0,95

100 0,96 -0,18 -0,200 13,98 0,18 1,50 0,96

Load MismatchOptimum energy transfer when ZS=ZL

(example w ith resistive loads)

0,00

0,20

0,40

0,60

0,80

1,00

1,20

0 50 100 150 200 250

Load impedance ZL [Ohm]PL Power in load [mW]

( )tVV ωsinˆ=

ZS

ZL

Signal Source

( ) ⎭⎬⎫

⎩⎨⎧

+= 2

2

2

ˆ

LS

LeL ZZ

ZVRP

( )2110 Γ−= LOGTL( )Γ= LOGRL 200

0

ZZZZ

ZZZZ

L

L

SL

SL

+−

=+−

=Γ

20

Smith Chart

• Graphic presentation of al

• Directly Display– Reflection coefficient – VSWR– Insertion loss– Return loss– Q-factor– Impedance/admittance

• Invaluable tool when making match circuits.

0}Re{ ≥Z

11

21

Schematic

CC2500EM schematic

22

Matching CC2500

12

23

Matching the CC11xx family (315/434MHz)

24

Matching the CC11xx family (868/915MHz)

Operation at 868MHz ETSI with antenna connector

13

25

• A very crucial component

• The purpose of an antenna:

– Transmit mode: Transform RF signals into electromagnetic waves, propagating into free space

– Receive mode: Transform electromagnetic waves into RF signals

TX

RX

Principle of Antennas

26

Frequency vs. Size

• Lower frequency gives better range– Reducing the frequency with a factor of two doubles the

range

• Lower frequency requires a larger antenna– λ/4 at 433 MHz is 17.3 cm– λ/4 at 915 MHz is 8.2 cm– λ/4 at 2.4 GHz is 3.1 cm

• A meandered structure can beused to reduce the size

14

27

Antenna Parameters

• Important parameters– Directivity, D. Difference between

maximum radiation intensity and average radiation intensity

– Gain, G. Describes efficiency and radiation properties

– Polarization. Describes the direction of the electric field

– Impedance. Describes how much of the available power that can be delivered to the antenna

– Bandwidth is the frequency band where the antenna has desired performance

avgUUD max=

DPPG

in

rad=

28

Gain 5.6 dBi4 dB/divFrequency 2.44 GHzHorizontal polarizationXY plane

Radiation Pattern (1)

• Radiation pattern for a folded dipole

15

29

• Influence from ground plane

Radiation Pattern (2)

With SmartRF04EB

+4.6 dBi Gain

Without SmartRF04EB

-1.2 dBi Gain

30

Agenda

• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)

16

31

Definitions (2)

• SensitivityLowest input power with acceptable link quality (typically 1% PER)

• PERPacket Error Rate, % of packets received not successfully

• Deviation/separationFrequency offset between a logic ‘0’ and ‘1’ using FSK modulation

• Blocking/selectivityHow well a chip works in an environment with interference

32

Low-Power Essentials

• Use the lowest possible duty cycle– Send data only when needed, do not send more data than

necessary

– Use the highest data rate you can (trade-off vs. range)

– Watch out for protocol-related overhead

• Use the lowest possible voltage– RF chips have reduced current draw at lower voltages

– Low voltage degrades RF performance

– Above not a problem if on-chip regulator

• Use a switch-mode regulator with low quiescent current to maximize battery lifetime

17

33

Waking up the Radio

• Waking up a radio from sleep takes it through several intermediate steps

• Calculate the average current to estimate battery lifetime

Current

Time

Power-downCrystal

oscillator start-up

PLL start-up Transmit/Receive Power-down

34

Polling Receiver

• Use a polling receiver if possible– Wakes up periodically and searches for data

– Timing depends on behavior of the transmitter

Power-down Wake up Check for data Power-down Wake up Check for

data

RX RX RX

TX

18

35

RX-TX Switching

• For 2 way protocols, go as quickly as possible from transmit to receive mode or vice versa

Worst case:

Best case:

Xtal start PLL start Transmit Power-downPower-down Xtal start PLL start Receive Power-down

Xtal start PLL start TransmitPower-down Receive Power-down

36

Discard False/Error Packets in RX

• Minimize time in RX processing false packets– Check carrier sense– Check for valid preamble– Check for valid sync word– Check length byte– Check for valid address

• Only notify MCU when a valid packet has been received– Automatic CRC check

• Packet discarded if CRC fails• Interrupt to MCU if CRC OK

19

37

Frequency Hopping System

• Fast settling PLL important to minimize blanking interval

• Minimize synchronization time

Frequency

ch1

Blanking interval

ch5

ch4

ch6

ch2

ch3

Time

38

2.4 GHz ISM-band devices

Source: Eliezer & Michael, TI

• Due to the world-wide availability of the 2.4GHz ISM band it is getting more crowded day by day• Devices such as Wi-Fi, Bluetooth, ZigBee, cordless phones, microwave ovens, wireless game

pads, toys, PC peripherals, wireless audio devices and many more occupy the 2.4 GHz frequency band

The figure below shows a common senario in a building with a WiFi access point, a microwave oven and a cordless phone

Power

Microwave oven

Cordless Frequency802.11b/g

20

39

Static Frequency Hopping

• Utilise a predetermined set of frequencies with either a repeating hop pattern or a pseudorandom hop pattern, e.g. Bluetooth (versions 1.0 and 1.1)

Power

Frequency 802.11b/g Microwave oven

Cordless

Source: Eliezer & Michael, TI

40

Adaptive Frequency Hopping

• Scan the entire frequency band at start-up and restrict usage to frequencies with the lowest energy content, e.g. RadioDesk and Bluetooth 1.2 and 2.0

• Substitute frequencies experiencing interference on the fly

Power

Frequency 802.11b/g microwave oven

cordlessSource: Eliezer & Michael, TI

21

41

Frequency Agility

• Frequency agility can be considered an extremely slow hopping frequency hopping system

• In a frequency agile system the frequency is first changed when the link performance is degraded, i.e. when the Packet Error Rate (PER) exceeds a predetermined threshold

Power

Frequency

1 2

42

What do I really receive?

• Your receiver will receive more than just the desired signal• Even if in interferer is sending on a nearby channels you will “loose” sensitivity• If you “loose” to much sensitivity you will not be able to receive anything even if you are

far away from the interferer

Power

Microwave oven

Cordless Frequency802.11b/g

Desired signal

Received

22

43

Selectivity / Channel rejection

How good is the receiver at handling interferers at same frequency and close by frequencies?

Desired signal / Interferer

Co-channel rejection

[dB]

Desired channel±FrequencyChannel

separation

Adjacent channel rejection

[dB]

Channel separation

Alternate channel rejection

[dB]

Power

44

RF is like a Cocktail Party

RF is like a cocktail party: It does not help to shout loud (high TX power) or to hear perfectly (good

sensitivity) if one is not able to select (good selectivity) what to listen to.

Shouting too loud (high TX power) can result in that no one can understand each other anymore due to the resulting noise

(interference from unwanted signals).

If it gets too noisy you will also have to repeat what you say often (re-transmit) which will cause you to work more (higher current

consumption)

23

45

Agenda

• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)

46

SmartRF05EB

24

47

CCMSP-EM430F2618

48

Use Cases

EM connector

Layer 1. SmartRF05EB

Layer 2. MSP430EM connector

Layer 3. Transceiver

SmartRF05EB + CCxxxx transceiver EMSmartRF Studio controlled or user application running on CC2511

SmartRF05EB + CCxxxx SoC EMSmartRF Studio controlled or user application running on SoC

SmartRF05EB + CCMSP-EM + CCxxxx EMUser application running on CCMSP-EM

CCMSP-EM + CCxxxx EMCCMSP-EM and transceiver standalone

25

49

SmartRF05EB + CCMSP-EM + CC2520EM

50

ZigBee Demonstration Kit

eZ430-RF2480

Based on the CC2480 – A ZigBee Network Processor

3x Target Boards2x Battery Boards1x USB debug dongle

Comes with a simple application that demonstrates

- Command interface- Chip configuration- Simple API- Basic network operations

A PC application shows the network topology

Price $99

CC2480 Antenna

MSP430F2274 2x LEDs

Button

GPIO

Light Sensor

26

51

MSP430 Experimenter’s Board

• MSP430FG4618 + F2013

• Supports selected Low Power RF Evaluation Modules

• Does not support SmartRF Studio

• Perfect for prototyping• Complete software libraries

and RF stacks available • MSP430 Interface to

CC1100/2500 Code Library• TIMAC (802.15.4) ported to

MSP430• Z-stack ported to MSP430• $99

Touc

h Pa

d

RF Expansion

Buzzer

AudioOut

RS232

Mic

52

Thank you