Introduction to RF design

Mexico – June 2008Mike Claassen

Agenda

• Part I: Getting Acquainted with the CC Portfolio– Overview of a Low Power Wireless System

• Overview of the TI Low Power Wireless Portfolio• Features of the CC2500/CC1100 Radios• Tools Overview: Packet Sniffer, RF Studio, RF Toolsticks

– Hands On – Performing a Simple Tx/Rx using the CC2500 and the RF Studio Software Design Tools

• Typical MSP430 / CC2500 Radio Connection• Overview of the RF Studio Sotware• Running a simple Tx/Rx while monitoring the CC2500 Radio Status

State Machine– Overview and Hands-On: Intermediate Radio Features

• Adding Variable Packet & Address Filtering• Adding GDO / GPIO Interrupts

– Overview and Demo of Advanced Radio Features• Frequency Hopping• Wake on Radio Power Profile

Agenda - Continued

• Part II: Getting Acquainted TI Stack Offering– Comparison of 802.15.4, SimpliciTI, and Zigbee Stacks

• Features and Benefits• What is right for your application• Device offering

– SimpliciTI Overview• SimpliciTI Components• Typical Network Topologies• Typical Payload Overview

– Hands On: Using SimpliciTI to Communicate End Device to End Device in a Typical Network

– Overview and Hands On: Adding an Access Point – Overview of the Zaccel Integrated Zigbee Modem– Hands On – Using Zaccel in a Zigbee Network

• Part III: Hardware Considerations for a LPW Design

Introduction to a Low Power Wireless System

• Definitions

• Radio Modulation Schemes

• Radio Frequency Spectrum

• Network Types

• Low Power RF Components

• Tools

Agenda

Definitions

RF Power Definitions

• dBm – power referred to 1 mW

PdBm=10log(P/1mW)0dBm = 1mW20 dBm = 100mW30 dBm = 1W-110dBm = 1E-11mW = 0.00001nW

50 Ω load : -110dBm is 0.7uV

• dBc – power referred to carrier

• Rule of thumb:

• 6dB increase => twice the range• 3dB increase => roughly doubles the

dbm power

dBm to Watt

About dBm and W

– Voltage Ratio aV = 20 log (P2/P1) [aV] = dB

– Power Ratio aP = 10 log (P2/P1) [aP] = dB

– Voltage Level V‘ = 20 log (V/1µV) [V‘] = dBµV

– Power Level P‘ = 10 log (P/1mW) [P‘] = dBm

e.g. 25mW max. allowed radiated power in the EU SRD bandP‘ = 10 log (25mW/1mW) = 10 * 1.39794 dBm ~ 14 dBm

dBm Typicals

dBm level Power Notes80 dBm 100 kW Typical transmission power of FM radio station with 30-40 miles range

60 dBm 1 kW Typical combined radiated RF power of microwave oven elements

36 dBm 4 W Typical maximum output power for a Citizens' band radio station(27 MHz) in many countries

30 dBm 1 W Typical RF leakage from a microwave oven - Maximum output power for DCS 1800 MHz mobile phone

27 dBm 500 mW Typical cellular phone transmission power

20 dBm 100 mW Bluetooth Class 1 radio, 100 m range (maximum output power from unlicensed FM transmitter). Typical wireless router transmission power.

4 dBm 2.5 mW Bluetooth Class 2 radio, 10 m range

0 dBm 1.0 mW Bluetooth standard (Class 3) radio, 1 m range

−10 dBm 100 µW Typical maximum received signal power (−10 to −30 dBm) of wireless network

−70 dBm 100 pW Typical range (−60 to −80 dBm) of Wireless received signal power over anetwork

−127.5 dBm 0.178 fW Typical received signal power from a GPS satellite

For more information: http://en.wikipedia.org/wiki/DBm

Radio Definitions

• PERPacket Error Rate, % of packets not received successfully

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

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

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

Radio Modulation Schemes

Wireless Communication Systems

Low Frequency Information Signal

(Intelligence)

High Frequency Carrier

Modulator Amplifier

Transmitter

Communication Channel

Amplifier Demodulator (detector)

Output transducer

Receiver

Amplifier

Modulation and Demodulation

digitalmodulation

digitaldata analog

modulation

radiocarrier

analogbasebandsignal

101101001 Radio Transmitter

synchronizationdecision

digitaldataanalog

demodulation

radiocarrier

analogbasebandsignal

101101001 Radio Receiver

Source: Lili Qiu

Clock and Data Recovery

• Data is asynchronous, no clock signal is transmitted. • Clock is recovered (trained) with the preamble.

Received Data Train

1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 0 1 0

Expected Preamble

4 clocks 2 clocks 1 clock

Recovered Clock Bit Time

Modulation Methods

• Starting point: We have a low frequency signal and want to send it at a high frequency

• Modulation: The process of superimposing a low frequency signal onto a high frequency carrier signal

• Three modulation schemes available:1. Amplitude Modulation (AM): the amplitude of the carrier varies

in accordance to the information signal2. Frequency Modulation (FM): the frequency of the carrier varies

in accordance to the information signal3. Phase Modulation (PM): the phase of the carrier varies in

accordance to the information signal

Digital Modulation – ASKThe modulation of digital signals is known as Shift KeyingAmplitude Shift Keying (ASK/OOK):

– Pros: simple, duty cycling (FCC), lower transmit current– Cons: susceptible to noise, wide spectrum noise

• Rise and fall rates of the carrier's amplitude can be adjusted to reduce the spectrum noise at low to medium data rates

• This is called Shaped OOK– Example: Many legacy wireless systems

1 0 1

t

Source: Lili Qiu

•Signal Space Diagram• Each axis represents a ‘symbol’

• OOK has two basis functions: sinusoid & no sinusoid

• OOK has two symbols: carrier & no carrier

• Distance between symbols predicts BER

10

Digital Modulation - FSKFrequency Shift Keying (FSK):

– Pros: Less susceptible to noise– Cons: Theoretically requires larger

bandwidth/bit than ASK– Popular in modern systems– Gaussian FSK (GFSK) has better

spectral density than 2-FSK modulation, i.e. more bandwidth efficient

1 0 1

t

1 0 1

Source: Lili Qiu

FSK modulation

FrequencyfcFc-df Fc+df

DIO=low DIO=high

Frequency deviation

Frequency separation= 2 x df

1

0

Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’

• Each basis function is ‘orthogonal’

• Distance between symbols predicts BER

Digital Modulation - PSK

Phase Shift Keying (PSK):– Pros:

• Less susceptible to noise• Bandwidth efficient

– Cons: Require synchronization in frequency and phase complicates receivers and transmitter

t

1 10

Source: Lili Qiu

10

Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’

• Each basis function is ‘orthogonal’

• Distance between symbols predicts BER

Digital Modulation – QPSK/OQPSKQuadrature Phase Shift Keying

– Pros: Symbol represents two bits of data– Cons: Phase in the signal can jump as

much as 180O causing out of band noise

Offest Quadrature Phase Shift Keying– Pros: Offsetting the signal limits the phase

jump to no more than 90O

http://en.wikipedia.org/wiki/Phase-shift_keying

2CA

1α

2α

2CA

11

10

00

01

Digital Modulation - MSKMinimum Shift Keying (MSK):

– Pros: Difference in Frequency is Half the bit rate– Very bandwidth efficient – Reduced Spectrum noise

– Cons: Require synchronization in frequency and phase complicates receivers and transmitter

– Example: IEEE 802.15.4 / ZigBee

t

1 10 0

10

Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’

• Each basis function is ‘orthogonal’

• Distance between symbols predicts BER

Radio Frequency Spectrum

Electromagnetic Spectrum

Source: JSC.MIL

SOUND LIGHTRADIO HARMFUL RADIATION

VHF = VERY HIGH FREQUENCYUHF = ULTRA HIGH FREQUENCYSHF = SUPER HIGH FREQUENCY EHF = EXTRA HIGH FREQUENCY

4G CELLULAR56-100 GHz

2.4 GHzISM band

ISM bands315-915 MHz

UWB3.1-10.6 GHz

ISM/SRD Bands

The 2400–2483.5 MHz band is available for license-free operation in most countries

• 2.4 GHz Pros– Same solution for all markets without SW/HW alterations– Large bandwidth available, allows many separate channels

and high datarates– 100% duty cycle is possible– More compact antenna solution than below 1 GHz

• 2.4 GHz Cons– Shorter range than a sub 1 GHz solution (with the same

current consumption)– Many possible interferers are present in the band

The “World-Wide” 2.4 GHz ISM Band

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

Power

Microwave oven

Cordless Frequency802.11b/g

• The ISM bands under 1 GHz are not world-wide

• Limitations vary a lot from region to region and getting a full overview is not an easy task– Sub 1GHz Pros

• Better range than 2.4 GHz with the same output power and current consumption (assuming a good antenna – not easy for a limited space)

– Sub 1GHz Cons• Since different bands are used in different markets it is

necessary with custom solutions for each market• More limitations to output power, data rate, bandwidth etc. than

the 2.4 GHz • Duty cycle restrictions in some regions• Interferers are present in most bands

Sub 1GHz ISM Bands

Sub 1GHz ISM bands• 902-928 MHz is the main frequency band

• The 260-470 MHz range is also available, but with more limitations

• The 902-928 MHz band is covered by FCC CFR 47, part 15

• Sharing of the bandwidth is done in the same way as for 2.4 GHz: • Higher output power is allowed if you spread your transmitted power and

don’t occupy one channel all the timeFCC CFR 47 part 15.247 covers wideband modulation

• Frequency Hopping Spread Spectrum (FHSS) with ≥50 channels are allowed up to 1 W, FHSS with 25-49 channels up to 0.25 W

• Direct Sequence Spread Spectrum (DSSS) and other digital modulation formats with bandwidth above 500 kHz are allowed up to 1W

• FCC CFR 47 part 15.249• ”Single channel systems” can only transmit with ~0.75 mW output power

Frequency Spectrum AllocationUnlicensed ISM/SRD bands:• USA/Canada:

– 260 – 470 MHz (FCC Part 15.231; 15.205)– 902 – 928 MHz (FCC Part 15.247; 15.249)– 2400 – 2483.5 MHz (FCC Part 15.247; 15.249)

• Europe:– 433.050 – 434.790 MHz (ETSI EN 300 220)– 863.0 – 870.0 MHz (ETSI EN 300 220)– 2400 – 2483.5 MHz (ETSI EN 300 440 or ETSI EN 300 328)

• Japan:– 315 MHz (Ultra low power applications)– 426-430, 449, 469 MHz (ARIB STD-T67)– 2400 – 2483.5 MHz (ARIB STD-T66)– 2471 – 2497 MHz (ARIB RCR STD-33)

ISM = Industrial, Scientific and MedicalSRD = Short Range Devices

Short-Range Wireless

Different Value Drivers for Different Applications

1000m

•Headsets•PC Peripherals•PDA/Phone

• Building Automation• Residential Control • Industrial • Tracking • Sensors• Home Automation / Security• Meter Reading

Data Rate (bps)

100k 1M 10M10k1k

Range

100m

10m

1m

ZigBee/802.15.4

•PC Networking•Home Networking•Video Distribution

Wi-Fi/802.11

Proprietary Low Power Radio•Gaming•PC Peripherals•Audio•Meter Reading•Building Mgmt.•Automotive

UWB•Wireless USB•Video/audio links

Sub 1GHz Product Selection

2.4GHz Portfolio

Stack Considerations

Physical

MAC

App

Software Stack Considerations

2.4 GHz/ ISM Band Radio Data

Preamble Sync Word Radio Payload (Max 255 Bytes)** Physical

Layer

Proprietary Radio – CC2500/CC1100

Length

Field*

Address

Field*

RSSI

LQI*

CRC 16

Check

Data Payload

(Max 60 Bytes)

Proprietary Stack

Up to 64 Bytes

2-24 Bytes 2or4 Bytes 1 Byte 1 Byte 0-60 Bytes 2 Bytes 2 Bytes

MAC

Layer

* Optional Settings for the radio – activating these settings drops the useable payload** Requires monitoring at refill of the 64Byte Tx Buffer

2.4G / ISM Band Radio Data

Preamble Sync Word Radio Payload (Max 64 Bytes)

Physical

MRFI

Layer

SimpliciTI Example – CC2500/CC1100

Length

Field

Address

Field Off

RSSI

LQI

CRC 16

Check

Data Payload

(Max 60 Bytes)

Custom Application

Up to 50 Bytes

2-24 Bytes 2or4 Bytes 1 Byte 0 – 61 Bytes 2 Bytes 2 Bytes

Destination

Address

MAC

LayerSource

Address

Port

Data

Device

Info

TractID

Info

4 Bytes 4 Bytes 1 Byte 1 Byte 1 Byte 0 to 50 Bytes

SimpliciTI

Payload

2.4G Radio Data

Synchronization

Header

Radio Specific

HeaderRadio Payload (Max 127 Bytes) Physical

Layer

Frame

Control

Sequence

Number

Address

Info

Frame

Check

Command

Payload

802.15.4 OSI Layers

Frame

Control

Sequence

Number

Address

Info

Frame

Check

Beacon

Payload

Frame

Control

Sequence

Number

Address

Info

Frame

Check

Data

Payload

Frame

Control

Sequence

Number

Frame

Check

MAC

Layer

Data Frame

Command Frame

Beacon Frame

ACK Frame

2 Bytes 1 Byte 0-20 Bytes <= 104B 2 Bytes

2.4G Radio Data

Synchronization

Header

Radio Specific

HeaderRadio Payload (Max 127 Bytes) Physical

Layer

Zigbee Stack on 802.15.4

Frame

Control

Sequence

Number

Address

Info

Frame

Check

Payload

<= 104BMAC

Layer802.15.4 Frame

2 Bytes 1 Byte 0-20 Bytes <= 104B 2 Bytes

Network Layer (NWK)

Application Layer (APS)

Zigbee Device

Object 0

Application

Object 1

Application

Object xxxSecurity

Service

Provider

Network Types

Network Types

Data pathPoint to Point

Network Types

Data pathStar

Network Types

Data pathMesh

Network Types

Data pathMesh

Which Protocol?

Radio HardwareProprietary

SimpliciTI 802.15.4 Zigbee

Best Suited Topology

Point to Point Point to PointStar Network

Star Network

Source & DestinationFair

Medium

CC2520CC2530

Mesh

Addressing Destination Source & Destination

Source & Destination

Code Size Minimal <1k Good < 4k Large < 64k

Complexity Low Medium Low - Zaccel

Target Devices

CC25x0CC11x0

CC25x0CC11x0

CC2480

Low Power RF Components

Basic Building Blocks of an RF System• RF-IC

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

typically transceiver with integrated uC

• 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

• Impedence Matching• Filter

– Used if needed to pass regulatory requirements / improve selectivity

• Antenna

RF-ICBalun

& Match

Filter

Crystal

Antenna(50Ω)

RF-ICs Examples• Transmitter

– CC1050, CC1150, and CC2550

• Transceiver – CC1100, CC2500, CC2400, and CC2420

• System-on-Chip (SoC) – Transceiver with a built-in micro controller– CC1110, CC2510, CC2430

Crystals• Provides reference frequency for Local Oscillator (LO) and

the carrier frequency• Important characteristics:

– Tolerance[ppm], both initial spread, aging & over temperature

– Price, often a price vs. performance trade-off– Size

• Various types:– Low Power crystals (32.768 kHz)

• Used with sleep modes on e.g. System-on-Chips – Crystals

• Thru hole• Tuning fork• SMD

– Temperature Controlled Crystal Oscillators (TCXO)• Temperature stability – some narrowband applications

– Voltage Controlled Crystal Oscillators (VCXO)– Oven Controlled Crystal Oscillators (OCXO)

• Extremely stable

Balun & Matching

Balun and matching towards antenna

Differential signal out of the chip

Single ended signal

Dig

ital I

ntef

ace

6 G

DO

0

7 C

Sn

8 XO

SC

_Q1

9 AV

DD

10 X

OSC

_Q2

SI 2

0

GN

D 1

9

DG

UA

RD

18

RBI

AS

17

GN

D 1

6

Antennas, commonly used

• PCB antennas– Little extra cost (PCB)– Size demanding at low frequencies– Good performance possible– Complicated to make good designs

• Whip antennas– Expensive (unless piece of wire)– Good performance– Hard to fit in may applications

• Chip antennas– Expensive– OK performance– Small size

Notes on Antennas

• The antenna is VERY important if long range is important

• A quarter wave antenna is an easy and good solution, but it is not small (433 MHz: 16.4 cm, 868 MHz: 8.2 cm)– You can “curl up” such an antenna and make a helical

antenna. This is often a good solution since it utilizes unused volume for a product.

• If you need long range and have limited space, then talk to an antenna expert !

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

RF-IC Balun & Match

2/1 Switch2/1 Switch

LNA

PA Filter

Crystal

Antenna(50Ω)

Adding an External PACC2420EM PA DESIGN• Signal from TXRX Switch pin level shifted and

buffered– Level in TX: 1.8 V, level for RX and all other

modes: 0V• CMOS & GaAs FET switches assures low RX

current consumption• Simpler control without external LNA

– No extra signal is needed from MCU to turn off LNA in low power modes

RF_P

TXRX_SWITCH

RF_N

CC2420

BALUN

TX/RX Switch

ANT

TX/RX Switch

PA

LP filter

TX path

RX path

Controllogic and

biasnetwork

19.7 mA19.7 mARX current

580 meter230 meterLine of Sight Range

-93.1 dBm-94 dBmSensitivity

9.5 dBm0 dBmOutput power

30.8 mA17.4 mATX current

CC2420EM w/PA

CC2420EM

19.7 mA19.7 mARX current

580 meter230 meterLine of Sight Range

-93.1 dBm-94 dBmSensitivity

9.5 dBm0 dBmOutput power

30.8 mA17.4 mATX current

CC2420EM w/PA

CC2420EM

Radio Range – Free Space Propagation

• How much loss can we have between TX and RX?• Friis’ transmission equation for free space propagation:

or

– Pt is the transmitted power, Pr is the received power– Gt is the transmitter, Gr is the receiver antenna gain– Lambda is the wavelength– d is the distance between transmitter and receiver, or the range

22

2

)4( dGGPP rtt

r πλ

=dGGPP rttr log204

log20 −⎟⎠⎞

⎜⎝⎛+++=πλ

d = λ PtGtGr4π Pr

Radio Range – ”real life”

• How much loss can we really have TX to RX?

• 120 dB link budget at 433 MHz gives approximately 2000 meters (Chipcon rule of thumb)

• Based on the emperical results above and Friis’equation estimates on real range can be made

• Rule of Thumb:– 6 dB improvement ~ twice the distance– Double the frequency ~ half the range (433 MHz longer range

than 868 MHz)

Important Factors for Radio Range

• Antenna (gain, sensitivity to body effects etc.)

• Sensitivity

• Channel Selectivity

• Output power

• Radio pollution (selectivity, blocking, IP3)

• Environment (Line of sight, obstructions, reflections, multi-path fading)

Development Tools and EVMs

SimpliciTI: eZ430 RF-2500

Zigbee: eZ430-RFZACC06

MSP430FG4619 Exp Board

CC2500EMK

USB FET

SOC: Smart RF 05EB

CC2500EMKLCD (SPI)

CC2511

USB

UARTJOYSTICK

POTMETER

Debug interface

IO jumpersJumpers for current measurements

BUTTONS

LED

Flash (SPI)

EMK Adapter

Interface with the MSP430 SmartRF05EB + CCMSP-EM + CCxxxxEM

MSP430F2618

32KHz XTAL

Slot for high

speed XTAL

SPI Modes

BSL interface

JTAG

interface

EM Connector

MSP430

ports

CC2500EMK

CC2520 Development kit

CC2520 DK: • 2 boards with the MSP430F2618 • 3 EMs + antennas (the small RF) boards• 3 EBs with LCD and USB (CC2511)• Packet Error Rate software

(runing on the MSP)• Smart RF studio• Packet sniffer (ZigBee) – March

CC2520 EMK:• 2 CC2520 EMs + 2 antennas

Software (free of charge for MSP430):• ZigBee stack (March 08)• IEEE 802.15.4 MAC• SimpliciTI – (March 08)

CC2520 EM

Free Design Tools – Packet Sniffer

http://www.ti.com/litv/zip/swrc045g

Free Design Tools – RF Studio

http://focus.ti.com/docs/toolsw/folders/print/smartrftm-studio.html

Software Stacks – Zigbee Z-Stack• Z-Stack™ is compliant with the ZigBee® 2006 specification and supports multiple

platforms including the CC2430 System-on-Chip and the CC2420 and MSP430 platform.

• Z-Stack also has support for CC2431 which enables users to create ZigBee applications that can change behavior based on the nodes current location in the network.

• The Z-Stack has been awarded the ZigBee Alliance's golden unit status by the ZigBee test house TÜV Rheinland and is used by thousands of ZigBee developers world wide.

• Z-Stack version 1.4.3 supports the application feature called SimpleAPI. This API was designed from the point of view of the application developer rather than the ZigBeespecification but it still provides a ZigBee Compliant Platform (ZCP). This is a good way for application developers to quickly build ZigBee-based wireless mesh networked applications. Two sample applications are provided to illustrate the use of the SimpleAPI, a sensor data collection network application and a home automation network application. The project file for the sample applications is in the Samples\SimpleApp.

• Z-Stack is well suited for:– Monitoring and control applications – Wireless sensor networks – Home and building automation – Alarm and security – Asset tracking – Applications where interoperability is required – Applications that require a free world wide ISM band (2.4 GHz)

http://focus.ti.com/docs/toolsw/folders/print/z-stack.html

Free Software Stacks - SimpliciTI

http://focus.ti.com/docs/toolsw/folders/print/simpliciti.html

Introduction to Low Power Wireless Devices

Questions?

Mike ClaassenTexas Instruments