Getting One Foot Into RF UPDATE - Semiconductor company ......ch3 Time 38 2.4 GHz ISM-band devices...
Transcript of Getting One Foot Into RF UPDATE - Semiconductor company ......ch3 Time 38 2.4 GHz ISM-band devices...
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6/6/2008 1
Getting One Foot Into RF
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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.
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Agenda
• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)
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ISM/SRD License-Free Frequency Bands
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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
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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
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License Free Sub 1 GHz bands
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ETSI Example
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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
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FCC Example (915 MHz and 2.4 GHz)
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Agenda
• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)
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Transmission MethodSignal System Complexity
Digital Modulation Techniques
AM, FM Scalar Signals
ASK, FSK, QPSKVector Signals
TDMA, CDMATime Variant
Signals
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Transmission Methods: DSSS and FHSS Power
FrequencyDSSS – Direct Sequence Spread Spectrum
FrequencyFHSS – Frequency Hopping Spread Spectrum
Power Narrow Band Transmission
Wide Band Transmission
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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
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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
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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
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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
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Balun
• There are different balun implementations – Trade-off: PCB area versus cost
Microstrip delay line
IC balun
Discrete balun
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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
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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
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Schematic
CC2500EM schematic
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Matching CC2500
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Matching the CC11xx family (315/434MHz)
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Matching the CC11xx family (868/915MHz)
Operation at 868MHz ETSI with antenna connector
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• 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
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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
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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=
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Gain 5.6 dBi4 dB/divFrequency 2.44 GHzHorizontal polarizationXY plane
Radiation Pattern (1)
• Radiation pattern for a folded dipole
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• Influence from ground plane
Radiation Pattern (2)
With SmartRF04EB
+4.6 dBi Gain
Without SmartRF04EB
-1.2 dBi Gain
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Agenda
• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)
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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
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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
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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
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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
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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
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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
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Frequency Hopping System
• Fast settling PLL important to minimize blanking interval
• Minimize synchronization time
Frequency
ch1
Blanking interval
ch5
ch4
ch6
ch2
ch3
Time
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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
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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
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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
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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
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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
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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
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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)
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Agenda
• Regulation Basics• Basic Building Blocks of an RF System• RF System Parameters • Getting Started (Interface to MSP430)
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SmartRF05EB
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CCMSP-EM430F2618
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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
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SmartRF05EB + CCMSP-EM + CC2520EM
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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
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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
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Thank you