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RF Basics, RF for Non-RF Engineers

                                          Dag Grini
           Program Manager, Low Power Wireless
                              Texas2006 Texas Instruments Inc, Slide 1
                                  ©
                                     Instruments
Agenda
• Basics
• Basic Building Blocks of an RF System
• RF Parameters and RF Measurement
  Equipment
• Support / getting started




                                  © 2006 Texas Instruments Inc, Slide 2
Definitions
• dBm – relative to 1 mW
• dBc – relative to carrier
• 10mW = 10dBm, 0dBm = 1mW
• -110dBm = 1E-11mW = 0.00001nW
• For a 50 ohm load :
  -110dBm is 0.7uV,
  i.e. not much!



• Rule of thumb:
     Double the power = 3 dB increase
     Half the power = 3 dB decrease



                                        © 2006 Texas Instruments Inc, Slide 3
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 band
   >> P‘ = 10 log (25mW/1mW) = 10 * 1,39794 dBm >> 14 dBm




                                                      © 2006 Texas Instruments Inc, Slide 4
Electromagnetic Spectrum
    SOUND                 RADIO                   LIGHT            HARMFUL RADIATION




                 VHF = VERY HIGH FREQUENCY                             2.4 GHz          4G CELLULAR
                 UHF = ULTRA HIGH FREQUENCY                          ISM band              56-100 GHz
                 SHF = SUPER HIGH FREQUENCY            ISM bands        UWB
                 EHF = EXTREMELY HIGH FREQUENCY      315-915 MHz
                                                                     3.1-10.6 GHz




ISM = Industrial, Scientific and Medical                                              Source: JSC.MIL
UWB = Ultra Wide Band                                                   © 2006 Texas Instruments Inc, Slide 5
Frequency Spectrum Allocation
• Unlicensed 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 Medical
    SRD = Short Range Devices
                                                                    © 2006 Texas Instruments Inc, Slide 6
ISM/SRD License-Free Frequency Bands




                            © 2006 Texas Instruments Inc, Slide 7
RF Communication Systems
• Simplex RF System
      A radio technology that allows only one-way communication from a
      transmitter to a receiver
      Examples: FM radio, Pagers, TV, One-way AMR systems



                          TX
        TX

                                                                           RX



 TX                                                                         RX


                                       TRX


      TX
                           TX
                                                            © 2006 Texas Instruments Inc, Slide 8
RF Communication Systems
• Half-duplex RF Systems
   Operation mode of a radio communication system in which each end can
   transmit and receive, but not simultaneously.
   Note: The communication is bidirectional over the same frequency, but
   unidirectional for the duration of a message. The devices need to be
   transceivers. Applies to most TDD and TDMA systems.
   Examples: Walkie-talkie, wireless keyboard mouse




                                                        © 2006 Texas Instruments Inc, Slide 9
RF Communication Systems
• Full-duplex RF Systems
   Radio systems in which each end can transmit and receive
   simultaneously
   Typically two frequencies are used to set up the communication channel.
   Each frequency is used solely for either transmitting or receiving. Applies
   to Frequency Division Duplex (FDD) systems.
   Example: Cellular phones, satellite communication




                                                            © 2006 Texas Instruments Inc, Slide 10
Agenda
• Basics
• Basic Building Blocks of an RF System
• RF Parameters and RF Measurement
  Equipment
• Support / getting started




                                 © 2006 Texas Instruments Inc, Slide 11
Wireless Communication Systems
                                                                   Transmitter


     Low Frequency
   Information Signal
      (Intelligence)

                             Modulator                      Amplifier

    High Frequency
        Carrier




                                      Communication
                                         Channel


                                                                            Receiver




                        Demodulator                                       Output
          Amplifier                             Amplifier
                         (detector)                                     transducer



                                                                   © 2006 Texas Instruments Inc, Slide 12
Modulation and Demodulation

                              analog
                              baseband
digital
                              signal
data            digital                      analog
101101001     modulation                    modulation                     Radio Transmitter

                                         radio
                                         carrier




                             analog
                             baseband
                                                             digital
                             signal
              analog                    synchronization      data
            demodulation                   decision       101101001        Radio Receiver

                   radio
                   carrier
                                                                                Source: Lili Qiu

                                                                       © 2006 Texas Instruments Inc, Slide 13
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 signal


• Three modulation schemes available:
  1. Amplitude Modulation (AM): the amplitude of the carrier varies in
     accordance to the information signal
  2. Frequency Modulation (FM): the frequency of the carrier varies in
     accordance to the information signal
  3. Phase Modulation (PM): the phase of the carrier varies in accordance to
     the information signal
                                                           © 2006 Texas Instruments Inc, Slide 14
Digital Modulation
• Modulation of digital signals is known as Shift Keying


• Amplitude Shift Keying (ASK):
   Pros: simple
   Cons: susceptible to noise
   Example: Many legacy wireless systems, e.g. AMR


                 1      0       1



                                    t




                                                              Source: Lili Qiu

                                                     © 2006 Texas Instruments Inc, Slide 15
Digital Modulation
• Frequency Shift Keying (FSK):
   Pros: less susceptible to noise
   Cons: theoretically requires larger bandwidth/bit than ASK
   Popular in modern systems
   Gaussian FSK (GFSK), e.g. used in Bluetooth, has better spectral density
   than 2-FSK modulation, i.e. more bandwidth efficient



                  1       0       1



                                      t


                  1       0       1

                                                                  Source: Lili Qiu

                                                         © 2006 Texas Instruments Inc, Slide 16
Digital Modulation
• Phase Shift Keying (PSK):
   Pros:
     – Less susceptible to noise
     – Bandwidth efficient
   Cons:
     – Require synchronization in frequency and phase    complicates
        receivers and transmitter
   Example: IEEE 802.15.4 / ZigBee



                      1       0      1



                                         t
                                                                 Source: Lili Qiu

                                                        © 2006 Texas Instruments Inc, Slide 17
Basic Building Blocks of an RF System
• RF-IC                               • Balun
                                          Balanced to unbalanced
    Transmitter
                                          Converts a differential signal to a
    Receiver                              single-ended signal or vice versa
    Transceiver                       • Matching
    System-on-Chip (SoC); typically
    transceiver with integrated       • Filter
    microcontroller                       Used if needed to pass regulatory
                                          requirements / improve
                                          selectivity
• Crystal
    Reference frequency for the LO    • Antenna
    and the carrier frequency




                                                       © 2006 Texas Instruments Inc, Slide 18
Transmitter
• Modern transmitters typically use fractional-N
  synthesizers
• For angle modulation like FSK, MSK, O-QPSK, the
  synthesizer frequency is adjusted
• For amplitude modulation like OOK and ASK, the
  amplifier level is adjusted
                                    Frequency deviation

                                    Frequency separation
                                    = 2 x df




                 Fc-df   fc Fc+df            Frequency
               DIO=low      DIO=high

                  FSK modulation                           © 2006 Texas Instruments Inc, Slide 19
Receiver Architecture
• Super heterodyne receiver – e.g. CC1000
   Converts the incoming signal to an Intermediate Frequency (IF) signal
   and performs:
    1. Carrier frequency tuning – selects desired signal
    2. Filtering – separates signal from other modulated signals picked up
    3. Amplification – compensates for transmission losses in the signal
       path




                                                          © 2006 Texas Instruments Inc, Slide 20
Receiver Architecture
• Image rejection receiver – e.g. CC1020
   The image frequency is an undesired input frequency that is capable of
   producing the same intermediate frequency (IF) as the desired input
   frequency produces




                                                         © 2006 Texas Instruments Inc, Slide 21
Crystals
• Provides reference frequency for Local Oscillator
  (LO) and the carrier frequency


• 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                                 © 2006 Texas Instruments Inc, Slide 22
Balun & Matching

                                                                               Differential signal
                         SI 20

                                  GND 19

                                           DGUARD 18

                                                       RBIAS 17

                                                                  GND 16       out of the chip
Digital Inteface




                                                                  10 XOSC_Q2
                                           8 XOSC_Q1
                         6 GDO0




                                                       9 AVDD
                                  7 CSn




Single ended signal


                   Balun and matching
                   towards antenna
                                                                                    © 2006 Texas Instruments Inc, Slide 23
Antennas
Commonly used antennas:
• 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
                                       © 2006 Texas Instruments Inc, Slide 24
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 !


                                                         © 2006 Texas Instruments Inc, Slide 25
Extending the Range of an RF System
1. Increase the Output                 3. Increase both output
   power                                  power and sensitivity
     Add an external Power Amplifier       Add PA and LNA
     (PA)

2. Increase the sensitivity            4. Use high gain antennas
     Add an external Low Noise             Regulatory requirements need to
     Amplifier (LNA)                       be followed




                                                         © 2006 Texas Instruments Inc, Slide 26
Adding an External PA
   CC2420EM 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 and 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



  CC2420                                                                                 ANT
                                                    TX path

                                                                                                              CC2420EM        CC2420EM
                                               PA                                                                             w/PA
     RF_P
                                TX/RX Switch                  LP filter   TX/RX Switch         TX current     17.4 mA         30.8 mA
     RF_N         BALUN                                                                        RX current     19.7 mA         19.7 mA
                                                    RX path



TXRX_SWITCH
                                                                                               Output         0 dBm           9.5 dBm
                                                                                               power
                                                                                               Sensitivity    -94 dBm         -93.1 dBm
                     Control
                    logic and                                                                  Line of        230 meter       580 meter
                       bias
                     network                                                                   Sight Range
                                                                                                     © 2006 Texas Instruments Inc, Slide 27
Radio Range – Free Space Propagation
• How much loss can we have between TX and RX?


• Friis’ transmission equation for free space
  propagation:

                            ⎛ λ       ⎞                    Pt Gt Gr λ2
  Pr = Pt + Gt + Gr + 20 log⎜         ⎟ − 20 log d or Pr =
                            ⎝ 4π      ⎠                    (4π ) 2 d 2

    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

                                                            © 2006 Texas Instruments Inc, Slide 28
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
                                            © 2006 Texas Instruments Inc, Slide 29
Radio Range – Important Factors
• Factors
   Antenna (gain, sensitivity to body effects etc.)
   Sensitivity
   Output power
   Radio pollution (selectivity, blocking, IP3)
   Environment (Line of sight, obstructions, reflections,
   multipath fading)




                                              © 2006 Texas Instruments Inc, Slide 30
Agenda
• Basics
• Basic Building Blocks of an RF System
• RF Parameters and RF Measurement
  Equipment
• Support / getting started




                                 © 2006 Texas Instruments Inc, Slide 31
Phase Noise
       Ideal oscillator                Actual oscillator with phase noise




             ωc                             ωc

                     Down Conversion (receivers):
        LO signal (no phase noise)
                    Interferer             Interferer




                                            ωIF
             ωo Wanted signal                                               Down-converted bands
                                           Wanted signal
                                                                            consist of two overlapping
        LO signal (with phase noise)                                        spectra, with the wanted
                      Interferer                                            signal suffering from
                                                                            significant noise due to
                                                                            the tail of the interferer
            ωo                               ωIF
                  Wanted signal
Interferer end up within the IF bandwidth and cannot be filtered out
                                                                                     © 2006 Texas Instruments Inc, Slide 32
Phase Noise

     Transmitters:
     Transmitters

     Nearby transmitter

                            Difficult to detect weak signal at ω2.
                            The wanted signal is corrupted by the phase noise tail
                            of the transmitter
          ω1 ω2

         Ideal oscillator


• Phase noise is a key parameter for transceivers
• CC1020: -90 dBc/Hz @ 12.5 kHz (narrowband)


                                                                     © 2006 Texas Instruments Inc, Slide 33
Narrowband Transmitter
• How good is the transmitter at making efficient use of
  the RF spectrum?


• OBW = Occupied Band Width
   Defined as BW with 99.5% of the total average power (ARIB)
   For 12.5 kHz channel spacing OBW < 8.5 kHz (ARIB)
   Measured using built-in function of spectrum analyzer




                                          Frequency
                    Bad          Good

                                                        © 2006 Texas Instruments Inc, Slide 34
Narrowband Transmitter
   • ACP = Adjacent Channel Power
          25 kHz channel spacing, 17 kHz BW
          12.5 kHz channel spacing, 8.5 kHz BW
          Measured using built-in function of spectrum analyzer
                        Adjacent   Signal     Adjacent
                        channel    channel    channel       Narrowband characteristics:
                                                            • Bandwidth efficient modulation
                          BW         BW         BW          (e.g. GFSK)
                                                            • Low data rate
CC1020: ACP = -51 dBc
                                                            • Low deviation




                                                         Frequency
   • Low phase noise                         key parameter for low ACP
   • ETSI: Absolute ACP requirement (dBm),
     ARIB: Relative (dBc)
                                                                       © 2006 Texas Instruments Inc, Slide 35
Receiver, Co-channel Rejection
• How good is the receiver at handling interferers at
  same frequency?
• Co-channel rejection, CC1020/CC1021 : -11dB
• Test method: Modulated interferer
    Wanted signal 3 dB above sensitivity limit




                           Co-channel rejection in dB




                             Frequency
                                                        © 2006 Texas Instruments Inc, Slide 36
Receiver Selectivity
• ACR = Adjacent Channel Rejection or
• ACS = Adjacent Channel Selectivity

                        Adjacent channel



                                                   • CC1020: 32dB @ 12.5 kHz
                  ACR
                                                   • Test method
                                                        Wanted 3dB above sensitivity level
      Desired channel
                                                        Interferer injected in the adjacent
                                                        channel



                                       Frequency

            Channel separation




                                                                      © 2006 Texas Instruments Inc, Slide 37
Receiver Selectivity
• Selectivity, measured for channels “further out”
  (alternate channel selectivity)
• Same test method as ACR/ACS
                           Interferer




             Selectivity


      Desired channel




                                          Frequency

            n*Channel separation, n=2,3,4...

• Low phase noise and narrow IF bandwith
   good ACR/ACS
                                                      © 2006 Texas Instruments Inc, Slide 38
Receiver Selectivity

                 Selectivity Requirement for different RF standards
Standard, Ch. Spacing Adjacent Channel Rejection Selectivity, other channels
ARIB, 12.5 kHz           30 dB (± 12.5kHz)       40 dB for all other channel
ARIB, 25 kHz             40 dB (± 25kHz)         40 dB for all other channel
ETSI class 1, 25 kHz     60 dB (± 25 kHz)        84 dB (± 1 MHz)
Bluetooth, 1 MHz         0 dB (± 1 MHz)          30 dB (± 2 MHz)              40 dB (± 3 MHz)
CC2400, 1 MHz (250kbit/s12 dB (± 1 MHz)           48 dB (± 2 MHz)             50 dB (± 3 MHz)
CC2400, 1 MHz (1Mbit/s) 0 dB (± 1 MHz)           20 dB (± 2 MHz)              41dB (± 3 MHz)
Zigbee (802.15.4), 5 MHz 0 dB (± 5 MHz)          30 dB for all other channels
CC2420, 5MHz              39/46 (+ - 5 MHz)       53/57 (+ - 10 MHz)




• CC1020 is ARIB compliant (12.5 and 25 kHz channels)



                                                                          © 2006 Texas Instruments Inc, Slide 39
Receiver, Blocking/desensitization
• Blocking/desensitization is a measure of how good a
  receiver is to reject an interferer “far away” (out of
  band) from the wanted signal
• Measured the same way as selectivity, but the
  interfering signal is usually not modulated
• CC1020 performance:
    1 MHz 60 dB
    2 MHz 70 dB
    10 MHZ 78 dB

• Blocking can be further improved with a SAW filter




                                            © 2006 Texas Instruments Inc, Slide 40
Image Rejection
• Image Rejection

                             IF-frequency




  Image frequency       LO        Desired frequency


                    • CC1000
                       – No image rejection           ωIF



                    • CC1020
                       – Image rejection
                                                      ωIF   © 2006 Texas Instruments Inc, Slide 41
Receiver Sensitivity
• How to achieve good RF sensitivity?


• Introduce high gain in front       Radio Transceiver                                       Antenna
  of the receiver                                         Balun
                                                                        BPF         LNA
    External LNA needed                            RF_N

                                                             LC
    Poor linearity (IP3)                           RF_P



    Poor blocking/selectivity
    “Removes” the losses in the
    SAW filter

• Lower noise bandwidth              Radio Transceiver                                       Antenna

  (narrowband)                                                LPF
                                                                                T/R Switch
    Blocking/linearity not changed               RF_OUT




    Good selectivity                              RF_IN




    Good frequency control needed
                                                                  © 2006 Texas Instruments Inc, Slide 42
RF Measurement Equipment
• Vector Network Analyzers
    Component Characterisation – insertion loss
    S-parameters - matching
• Spectrum Analyzers
    Output Power, harmonics, spurious emission
    Phase Noise
    ACP
    OBW
    Modulation - deviation
• Signal Generators
    Sensitivity (BER option needed)
    Selectivity/blocking
    Two-tone measurements – IP3
• Power Meters
    Output Power – calibration
• Oscilloscopes
    Digital signal analysis
• Function and Arbitrary Waveform Generators
                                                  © 2006 Texas Instruments Inc, Slide 43
2.4 GHz ISM-band devices
• 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




            802.11b/g   Microwave   Cordless           Frequency
                        oven                   Source: Eliezer & Michael, TI
                                                 © 2006 Texas Instruments Inc, Slide 44
Spread Spectrum Systems
• Data sent using spread spectrum is intentionally
  spread over a wide frequency range

• Appears as noise, so it is difficult to detect and jam

• Resistant to noise and interference thus increasing
  the probability that the signal will be received
  correctly

• Unlikely to interfere with other signals even if they
  are transmitted on the same frequency

• 2 types of Spread Spectrum common in ISM bands:
    Direct Sequence Spread Spectrum (DSSS)
    Frequency Hopping Spread Spectrum (FHSS)
                                               © 2006 Texas Instruments Inc, Slide 45
General Model of a Spread Spectrum System



Input Data
                                                                                               Output Data
             Channel                      Communication                          Channel
                             Modulator                    Demodulator
             Encoder                         Channel                             Decoder

                       Spreading                                 Spreading
                         Code                                      Code

                           Pseudorandom                   Pseudorandom
                               Noise                          Noise




                                                                             © 2006 Texas Instruments Inc, Slide 46
Direct Sequence Spread Spectrum
               • Each bit represented by multiple bits using spreading
                 code
               • Spreading code spreads signal across wider
                 frequency band
               • Good resistance against interferers
                                                  RBW   100 kHz   RF Att      30 dB
       Ref Lvl                                    VBW   100 kHz
        0 dBm                                     SWT    5 ms     Unit           dBm
   0

                                                                                       A

 -10



 -20



 -30
        1AVG                                                                           1SA

 -40



 -50



 -60



 -70



 -80



 -90



-100
       Center 2.45 GHz                   1 MHz/                          Span 10 MHz

Date:           23.OCT.2003   21:34:19
                                                                                             © 2006 Texas Instruments Inc, Slide 47
DSSS – BPSK Example




                          Source: William Stalling
                      © 2006 Texas Instruments Inc, Slide 48
DSSS Spreading Mechanism
IEEE 802.15.4 (CC2420): 2 Mchips/s -> 250 kbps data rate
• 4 bits (nibble) are coded into 32 chips using a look-up
  table
      RX correlation example:
           Correct chip sequence for nibble = 5:
            0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0
           Incoming chip sequence (value is 5, but with 8 faulty chips):
            0 1 1 1 0 1 1 1 0 0 0 0 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 1 1 1 0 0
  Nibble                                                                                                                   Correlation
  value    Comparison (XOR) with all possible chip sequences                                                               value
    0       1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0                  1   0   1   0   0   1   0   0   0   1   0   1   1   1   0   18
    1       1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0                  0   1   1   0   1   0   1   0   0   1   0   0   0   1   0   16
    2       0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1                  1   0   0   0   0   1   1   0   1   0   1   0   0   1   0   14
    3       0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1                  0   0   1   1   1   0   0   0   0   1   1   0   1   0   1   12
    4       0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1                  1   0   1   1   0   0   1   1   1   0   0   0   0   1   1   14
    5       0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1                  1   1   0   1   1   0   1   1   0   0   1   1   1   0   0   24
    6       1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0                  0   1   0   1   1   1   0   1   1   0   1   1   0   0   1   16
    7       1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0                  0   1   0   0   0   1   0   1   1   1   0   1   1   0   1   14
    8       1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0                  0   0   0   0   1   1   1   0   1   1   1   1   0   1   1   14
    9       1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0                  1   1   0   0   0   0   0   0   1   1   1   0   1   1   1   16
   10       0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1                  0   0   1   0   1   1   0   0   0   0   0   0   1   1   1    14
   11       0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1                  1   0   0   1   0   0   1   0   1   1   0   0   0   0   0    20
   12       0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1                  0   0   0   1   1   0   0   1   0   0   1   0   1   1   0    14
   13       0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1                  0   1   1   1   0   0   0   1   1   0   0   1   0   0   1    12
   14       1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0                  1   1   1   1   0   1   1   1   0   0   0   1   1   0   0    20
   15       1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0                  1   1   1   0   1   1   1   1   0   1   1   1   0   0   0    18
                                                                                                                       © 2006 Texas Instruments Inc, Slide 49
DSSS – Co-existence Performance
• CC2420 - In-band interference
• Power of interferer only 1 dB lower than CC2420 transmitter, NO
  packet errors
• Narrowband interferer shown as peak in the centre on top of the
  CC2420 spread spectrum
• A typical FSK receiver requires the desired signal to be 11 dB
  above interferer




                                                    © 2006 Texas Instruments Inc, Slide 50
Frequency Hopping Spread
    Spectrum (FHSS)
    • Signal broadcast over a seemingly random series of
      frequencies
    • Receiver hops between frequencies in sync with
      transmitter
    • Jamming on one frequency affects only a few bits


          Power




Source: Eliezer & Michael, TI                                Frequency
                                             © 2006 Texas Instruments Inc, Slide 51
2.4 GHz Devices – 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




             802.11b/g   Microwave   Cordless                     Frequency
                         oven
                                                Source: Eliezer & Michael, TI
                                                    © 2006 Texas Instruments Inc, Slide 52
2.4 GHz – Adaptive Frequency Hopping
• Scan the entire frequency band at start-up and
  restrict usage to frequencies with the lowest energy
  content. RadioDesk and Bluetooth 1.2 and 2.0 are
  using AFH.
• Substitute frequencies experiencing interference on
  the fly.
 Power




             802.11b/g   microwave cordless            Frequency
                                              Source: Eliezer & Michael, TI
                         oven                 © 2006 Texas Instruments Inc, Slide 53
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           1               2




                                                     Frequency
                                          © 2006 Texas Instruments Inc, Slide 54
Agenda
• Basics
• Basic Building Blocks of an RF System
• RF Parameters and RF Measurement
  Equipment
• Support / getting started




                                 © 2006 Texas Instruments Inc, Slide 55
Getting Started
• Define and specify the product
   Following a standard or going proprietary?
   Power consumption
   Range and regulatory requirements – frequency of operation
   Data rate
   RF protocol
   SW content
   Analyse test tool and instrumentation needs
   Cost
• Compare different vendors – choose RF-IC & tools
   Purchase and evaluate EVMs and required tools
   What SW examples, application notes and documentation are available?
• Develop, co-operate or outsource?
   Sufficient resources available?
   Do you have the necessary competence in-house?
   Compliance testing?
                                                        © 2006 Texas Instruments Inc, Slide 56
Support
• Search for the relevant information
    Documentation – e.g. data sheets, user guides and application notes
    Knowledge bases
    SW examples

• Contact your local distributor or TI directly:
    Internet:
    TI Low Power Wireless home page:
       – http://www.ti.com/lpw
    TI MSP430 home page:
       – http://www.ti.com/msp430
    TI Semiconductor Product Information Center Home Page:
       – http://support.ti.com
    TI Semiconductor KnowledgeBase Home Page:
       – http://support.ti.com/sc/knowledgebase

                                                          © 2006 Texas Instruments Inc, Slide 57
Summary
• RF Basics
   Available frequency bands
   RF communication systems
   Modulation and demodulation
   Basic building blocks of an RF system – components
   Extending range
   Key RF parameters
   RF measurement equipment
   Spread spectrum systems – DSSS / FHSS / Frequency Agility
   Getting started
   Support




                                                      © 2006 Texas Instruments Inc, Slide 58
Thank you for your attention!

        Questions?




                      SLAP127   © 2006 Texas Instruments Inc, Slide 59
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements,
improvements, and other changes to its products and services at any time and to discontinue any product or service without notice.
Customers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All products are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.
TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s
standard warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this
warranty. Except where mandated by government requirements, testing of all parameters of each product is not necessarily
performed.
TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and
applications using TI components. To minimize the risks associated with customer products and applications, customers should
provide adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask
work right, or other TI intellectual property right relating to any combination, machine, or process in which TI products or services
are used. Information published by TI regarding third-party products or services does not constitute a license from TI to use such
products or services or a warranty or endorsement thereof. Use of such information may require a license from a third party under
the patents or other intellectual property of the third party, or a license from TI under the patents or other intellectual property of TI.
Reproduction of information in TI data books or data sheets is permissible only if reproduction is without alteration and is
accompanied by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an
unfair and deceptive business practice. TI is not responsible or liable for such altered documentation.
Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service
voids all express and any implied warranties for the associated TI product or service and is an unfair and deceptive business
practice. TI is not responsible or liable for any such statements.
TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would
reasonably be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement
specifically governing such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications
of their applications, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related
requirements concerning their products and any use of TI products in such safety-critical applications, notwithstanding any
applications-related information or support that may be provided by TI. Further, Buyers must fully indemnify TI and its
representatives against any damages arising out of the use of TI products in such safety-critical applications.
TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are
specifically designated by TI as military-grade or "enhanced plastic." Only products designated by TI as military-grade meet military
specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is
solely at the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in
connection with such use.
TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products
are designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any
non-designated products in automotive applications, TI will not be responsible for any failure to meet such requirements.
Following are URLs where you can obtain information on other Texas Instruments products and application solutions:

Products                                                Applications
Amplifiers           amplifier.ti.com                   Audio                         www.ti.com/audio
Data Converters      dataconverter.ti.com               Automotive                    www.ti.com/automotive
DSP                  dsp.ti.com                         Broadband                     www.ti.com/broadband
Interface            interface.ti.com                   Digital Control               www.ti.com/digitalcontrol
Logic                logic.ti.com                       Military                      www.ti.com/military
Power Mgmt           power.ti.com                       Optical Networking            www.ti.com/opticalnetwork
Microcontrollers     microcontroller.ti.com             Security                      www.ti.com/security
RFID                 www.ti-rfid.com                    Telephony                     www.ti.com/telephony
Low Power            www.ti.com/lpw                     Video & Imaging               www.ti.com/video
Wireless
                                                        Wireless                      www.ti.com/wireless

                         Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
                                        Copyright © 2007, Texas Instruments Incorporated

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Rf basics

  • 1. RF Basics, RF for Non-RF Engineers Dag Grini Program Manager, Low Power Wireless Texas2006 Texas Instruments Inc, Slide 1 © Instruments
  • 2. Agenda • Basics • Basic Building Blocks of an RF System • RF Parameters and RF Measurement Equipment • Support / getting started © 2006 Texas Instruments Inc, Slide 2
  • 3. Definitions • dBm – relative to 1 mW • dBc – relative to carrier • 10mW = 10dBm, 0dBm = 1mW • -110dBm = 1E-11mW = 0.00001nW • For a 50 ohm load : -110dBm is 0.7uV, i.e. not much! • Rule of thumb: Double the power = 3 dB increase Half the power = 3 dB decrease © 2006 Texas Instruments Inc, Slide 3
  • 4. 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 band >> P‘ = 10 log (25mW/1mW) = 10 * 1,39794 dBm >> 14 dBm © 2006 Texas Instruments Inc, Slide 4
  • 5. Electromagnetic Spectrum SOUND RADIO LIGHT HARMFUL RADIATION VHF = VERY HIGH FREQUENCY 2.4 GHz 4G CELLULAR UHF = ULTRA HIGH FREQUENCY ISM band 56-100 GHz SHF = SUPER HIGH FREQUENCY ISM bands UWB EHF = EXTREMELY HIGH FREQUENCY 315-915 MHz 3.1-10.6 GHz ISM = Industrial, Scientific and Medical Source: JSC.MIL UWB = Ultra Wide Band © 2006 Texas Instruments Inc, Slide 5
  • 6. Frequency Spectrum Allocation • Unlicensed 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 Medical SRD = Short Range Devices © 2006 Texas Instruments Inc, Slide 6
  • 7. ISM/SRD License-Free Frequency Bands © 2006 Texas Instruments Inc, Slide 7
  • 8. RF Communication Systems • Simplex RF System A radio technology that allows only one-way communication from a transmitter to a receiver Examples: FM radio, Pagers, TV, One-way AMR systems TX TX RX TX RX TRX TX TX © 2006 Texas Instruments Inc, Slide 8
  • 9. RF Communication Systems • Half-duplex RF Systems Operation mode of a radio communication system in which each end can transmit and receive, but not simultaneously. Note: The communication is bidirectional over the same frequency, but unidirectional for the duration of a message. The devices need to be transceivers. Applies to most TDD and TDMA systems. Examples: Walkie-talkie, wireless keyboard mouse © 2006 Texas Instruments Inc, Slide 9
  • 10. RF Communication Systems • Full-duplex RF Systems Radio systems in which each end can transmit and receive simultaneously Typically two frequencies are used to set up the communication channel. Each frequency is used solely for either transmitting or receiving. Applies to Frequency Division Duplex (FDD) systems. Example: Cellular phones, satellite communication © 2006 Texas Instruments Inc, Slide 10
  • 11. Agenda • Basics • Basic Building Blocks of an RF System • RF Parameters and RF Measurement Equipment • Support / getting started © 2006 Texas Instruments Inc, Slide 11
  • 12. Wireless Communication Systems Transmitter Low Frequency Information Signal (Intelligence) Modulator Amplifier High Frequency Carrier Communication Channel Receiver Demodulator Output Amplifier Amplifier (detector) transducer © 2006 Texas Instruments Inc, Slide 12
  • 13. Modulation and Demodulation analog baseband digital signal data digital analog 101101001 modulation modulation Radio Transmitter radio carrier analog baseband digital signal analog synchronization data demodulation decision 101101001 Radio Receiver radio carrier Source: Lili Qiu © 2006 Texas Instruments Inc, Slide 13
  • 14. 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 signal • Three modulation schemes available: 1. Amplitude Modulation (AM): the amplitude of the carrier varies in accordance to the information signal 2. Frequency Modulation (FM): the frequency of the carrier varies in accordance to the information signal 3. Phase Modulation (PM): the phase of the carrier varies in accordance to the information signal © 2006 Texas Instruments Inc, Slide 14
  • 15. Digital Modulation • Modulation of digital signals is known as Shift Keying • Amplitude Shift Keying (ASK): Pros: simple Cons: susceptible to noise Example: Many legacy wireless systems, e.g. AMR 1 0 1 t Source: Lili Qiu © 2006 Texas Instruments Inc, Slide 15
  • 16. Digital Modulation • Frequency Shift Keying (FSK): Pros: less susceptible to noise Cons: theoretically requires larger bandwidth/bit than ASK Popular in modern systems Gaussian FSK (GFSK), e.g. used in Bluetooth, has better spectral density than 2-FSK modulation, i.e. more bandwidth efficient 1 0 1 t 1 0 1 Source: Lili Qiu © 2006 Texas Instruments Inc, Slide 16
  • 17. Digital Modulation • Phase Shift Keying (PSK): Pros: – Less susceptible to noise – Bandwidth efficient Cons: – Require synchronization in frequency and phase complicates receivers and transmitter Example: IEEE 802.15.4 / ZigBee 1 0 1 t Source: Lili Qiu © 2006 Texas Instruments Inc, Slide 17
  • 18. Basic Building Blocks of an RF System • RF-IC • Balun Balanced to unbalanced Transmitter Converts a differential signal to a Receiver single-ended signal or vice versa Transceiver • Matching System-on-Chip (SoC); typically transceiver with integrated • Filter microcontroller Used if needed to pass regulatory requirements / improve selectivity • Crystal Reference frequency for the LO • Antenna and the carrier frequency © 2006 Texas Instruments Inc, Slide 18
  • 19. Transmitter • Modern transmitters typically use fractional-N synthesizers • For angle modulation like FSK, MSK, O-QPSK, the synthesizer frequency is adjusted • For amplitude modulation like OOK and ASK, the amplifier level is adjusted Frequency deviation Frequency separation = 2 x df Fc-df fc Fc+df Frequency DIO=low DIO=high FSK modulation © 2006 Texas Instruments Inc, Slide 19
  • 20. Receiver Architecture • Super heterodyne receiver – e.g. CC1000 Converts the incoming signal to an Intermediate Frequency (IF) signal and performs: 1. Carrier frequency tuning – selects desired signal 2. Filtering – separates signal from other modulated signals picked up 3. Amplification – compensates for transmission losses in the signal path © 2006 Texas Instruments Inc, Slide 20
  • 21. Receiver Architecture • Image rejection receiver – e.g. CC1020 The image frequency is an undesired input frequency that is capable of producing the same intermediate frequency (IF) as the desired input frequency produces © 2006 Texas Instruments Inc, Slide 21
  • 22. Crystals • Provides reference frequency for Local Oscillator (LO) and the carrier frequency • 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 © 2006 Texas Instruments Inc, Slide 22
  • 23. Balun & Matching Differential signal SI 20 GND 19 DGUARD 18 RBIAS 17 GND 16 out of the chip Digital Inteface 10 XOSC_Q2 8 XOSC_Q1 6 GDO0 9 AVDD 7 CSn Single ended signal Balun and matching towards antenna © 2006 Texas Instruments Inc, Slide 23
  • 24. Antennas Commonly used antennas: • 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 © 2006 Texas Instruments Inc, Slide 24
  • 25. 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 ! © 2006 Texas Instruments Inc, Slide 25
  • 26. Extending the Range of an RF System 1. Increase the Output 3. Increase both output power power and sensitivity Add an external Power Amplifier Add PA and LNA (PA) 2. Increase the sensitivity 4. Use high gain antennas Add an external Low Noise Regulatory requirements need to Amplifier (LNA) be followed © 2006 Texas Instruments Inc, Slide 26
  • 27. Adding an External PA CC2420EM 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 and 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 CC2420 ANT TX path CC2420EM CC2420EM PA w/PA RF_P TX/RX Switch LP filter TX/RX Switch TX current 17.4 mA 30.8 mA RF_N BALUN RX current 19.7 mA 19.7 mA RX path TXRX_SWITCH Output 0 dBm 9.5 dBm power Sensitivity -94 dBm -93.1 dBm Control logic and Line of 230 meter 580 meter bias network Sight Range © 2006 Texas Instruments Inc, Slide 27
  • 28. Radio Range – Free Space Propagation • How much loss can we have between TX and RX? • Friis’ transmission equation for free space propagation: ⎛ λ ⎞ Pt Gt Gr λ2 Pr = Pt + Gt + Gr + 20 log⎜ ⎟ − 20 log d or Pr = ⎝ 4π ⎠ (4π ) 2 d 2 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 © 2006 Texas Instruments Inc, Slide 28
  • 29. 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 © 2006 Texas Instruments Inc, Slide 29
  • 30. Radio Range – Important Factors • Factors Antenna (gain, sensitivity to body effects etc.) Sensitivity Output power Radio pollution (selectivity, blocking, IP3) Environment (Line of sight, obstructions, reflections, multipath fading) © 2006 Texas Instruments Inc, Slide 30
  • 31. Agenda • Basics • Basic Building Blocks of an RF System • RF Parameters and RF Measurement Equipment • Support / getting started © 2006 Texas Instruments Inc, Slide 31
  • 32. Phase Noise Ideal oscillator Actual oscillator with phase noise ωc ωc Down Conversion (receivers): LO signal (no phase noise) Interferer Interferer ωIF ωo Wanted signal Down-converted bands Wanted signal consist of two overlapping LO signal (with phase noise) spectra, with the wanted Interferer signal suffering from significant noise due to the tail of the interferer ωo ωIF Wanted signal Interferer end up within the IF bandwidth and cannot be filtered out © 2006 Texas Instruments Inc, Slide 32
  • 33. Phase Noise Transmitters: Transmitters Nearby transmitter Difficult to detect weak signal at ω2. The wanted signal is corrupted by the phase noise tail of the transmitter ω1 ω2 Ideal oscillator • Phase noise is a key parameter for transceivers • CC1020: -90 dBc/Hz @ 12.5 kHz (narrowband) © 2006 Texas Instruments Inc, Slide 33
  • 34. Narrowband Transmitter • How good is the transmitter at making efficient use of the RF spectrum? • OBW = Occupied Band Width Defined as BW with 99.5% of the total average power (ARIB) For 12.5 kHz channel spacing OBW < 8.5 kHz (ARIB) Measured using built-in function of spectrum analyzer Frequency Bad Good © 2006 Texas Instruments Inc, Slide 34
  • 35. Narrowband Transmitter • ACP = Adjacent Channel Power 25 kHz channel spacing, 17 kHz BW 12.5 kHz channel spacing, 8.5 kHz BW Measured using built-in function of spectrum analyzer Adjacent Signal Adjacent channel channel channel Narrowband characteristics: • Bandwidth efficient modulation BW BW BW (e.g. GFSK) • Low data rate CC1020: ACP = -51 dBc • Low deviation Frequency • Low phase noise key parameter for low ACP • ETSI: Absolute ACP requirement (dBm), ARIB: Relative (dBc) © 2006 Texas Instruments Inc, Slide 35
  • 36. Receiver, Co-channel Rejection • How good is the receiver at handling interferers at same frequency? • Co-channel rejection, CC1020/CC1021 : -11dB • Test method: Modulated interferer Wanted signal 3 dB above sensitivity limit Co-channel rejection in dB Frequency © 2006 Texas Instruments Inc, Slide 36
  • 37. Receiver Selectivity • ACR = Adjacent Channel Rejection or • ACS = Adjacent Channel Selectivity Adjacent channel • CC1020: 32dB @ 12.5 kHz ACR • Test method Wanted 3dB above sensitivity level Desired channel Interferer injected in the adjacent channel Frequency Channel separation © 2006 Texas Instruments Inc, Slide 37
  • 38. Receiver Selectivity • Selectivity, measured for channels “further out” (alternate channel selectivity) • Same test method as ACR/ACS Interferer Selectivity Desired channel Frequency n*Channel separation, n=2,3,4... • Low phase noise and narrow IF bandwith good ACR/ACS © 2006 Texas Instruments Inc, Slide 38
  • 39. Receiver Selectivity Selectivity Requirement for different RF standards Standard, Ch. Spacing Adjacent Channel Rejection Selectivity, other channels ARIB, 12.5 kHz 30 dB (± 12.5kHz) 40 dB for all other channel ARIB, 25 kHz 40 dB (± 25kHz) 40 dB for all other channel ETSI class 1, 25 kHz 60 dB (± 25 kHz) 84 dB (± 1 MHz) Bluetooth, 1 MHz 0 dB (± 1 MHz) 30 dB (± 2 MHz) 40 dB (± 3 MHz) CC2400, 1 MHz (250kbit/s12 dB (± 1 MHz) 48 dB (± 2 MHz) 50 dB (± 3 MHz) CC2400, 1 MHz (1Mbit/s) 0 dB (± 1 MHz) 20 dB (± 2 MHz) 41dB (± 3 MHz) Zigbee (802.15.4), 5 MHz 0 dB (± 5 MHz) 30 dB for all other channels CC2420, 5MHz 39/46 (+ - 5 MHz) 53/57 (+ - 10 MHz) • CC1020 is ARIB compliant (12.5 and 25 kHz channels) © 2006 Texas Instruments Inc, Slide 39
  • 40. Receiver, Blocking/desensitization • Blocking/desensitization is a measure of how good a receiver is to reject an interferer “far away” (out of band) from the wanted signal • Measured the same way as selectivity, but the interfering signal is usually not modulated • CC1020 performance: 1 MHz 60 dB 2 MHz 70 dB 10 MHZ 78 dB • Blocking can be further improved with a SAW filter © 2006 Texas Instruments Inc, Slide 40
  • 41. Image Rejection • Image Rejection IF-frequency Image frequency LO Desired frequency • CC1000 – No image rejection ωIF • CC1020 – Image rejection ωIF © 2006 Texas Instruments Inc, Slide 41
  • 42. Receiver Sensitivity • How to achieve good RF sensitivity? • Introduce high gain in front Radio Transceiver Antenna of the receiver Balun BPF LNA External LNA needed RF_N LC Poor linearity (IP3) RF_P Poor blocking/selectivity “Removes” the losses in the SAW filter • Lower noise bandwidth Radio Transceiver Antenna (narrowband) LPF T/R Switch Blocking/linearity not changed RF_OUT Good selectivity RF_IN Good frequency control needed © 2006 Texas Instruments Inc, Slide 42
  • 43. RF Measurement Equipment • Vector Network Analyzers Component Characterisation – insertion loss S-parameters - matching • Spectrum Analyzers Output Power, harmonics, spurious emission Phase Noise ACP OBW Modulation - deviation • Signal Generators Sensitivity (BER option needed) Selectivity/blocking Two-tone measurements – IP3 • Power Meters Output Power – calibration • Oscilloscopes Digital signal analysis • Function and Arbitrary Waveform Generators © 2006 Texas Instruments Inc, Slide 43
  • 44. 2.4 GHz ISM-band devices • 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 802.11b/g Microwave Cordless Frequency oven Source: Eliezer & Michael, TI © 2006 Texas Instruments Inc, Slide 44
  • 45. Spread Spectrum Systems • Data sent using spread spectrum is intentionally spread over a wide frequency range • Appears as noise, so it is difficult to detect and jam • Resistant to noise and interference thus increasing the probability that the signal will be received correctly • Unlikely to interfere with other signals even if they are transmitted on the same frequency • 2 types of Spread Spectrum common in ISM bands: Direct Sequence Spread Spectrum (DSSS) Frequency Hopping Spread Spectrum (FHSS) © 2006 Texas Instruments Inc, Slide 45
  • 46. General Model of a Spread Spectrum System Input Data Output Data Channel Communication Channel Modulator Demodulator Encoder Channel Decoder Spreading Spreading Code Code Pseudorandom Pseudorandom Noise Noise © 2006 Texas Instruments Inc, Slide 46
  • 47. Direct Sequence Spread Spectrum • Each bit represented by multiple bits using spreading code • Spreading code spreads signal across wider frequency band • Good resistance against interferers RBW 100 kHz RF Att 30 dB Ref Lvl VBW 100 kHz 0 dBm SWT 5 ms Unit dBm 0 A -10 -20 -30 1AVG 1SA -40 -50 -60 -70 -80 -90 -100 Center 2.45 GHz 1 MHz/ Span 10 MHz Date: 23.OCT.2003 21:34:19 © 2006 Texas Instruments Inc, Slide 47
  • 48. DSSS – BPSK Example Source: William Stalling © 2006 Texas Instruments Inc, Slide 48
  • 49. DSSS Spreading Mechanism IEEE 802.15.4 (CC2420): 2 Mchips/s -> 250 kbps data rate • 4 bits (nibble) are coded into 32 chips using a look-up table RX correlation example: Correct chip sequence for nibble = 5: 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 Incoming chip sequence (value is 5, but with 8 faulty chips): 0 1 1 1 0 1 1 1 0 0 0 0 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 1 1 1 0 0 Nibble Correlation value Comparison (XOR) with all possible chip sequences value 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 18 1 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 16 2 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 14 3 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 12 4 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 0 0 1 1 14 5 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1 0 0 24 6 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 1 0 0 1 16 7 1 0 0 1 1 1 0 0 0 0 1 1 0 1 0 1 0 0 1 0 0 0 1 0 1 1 1 0 1 1 0 1 14 8 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 14 9 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 16 10 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 14 11 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 20 12 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 1 0 14 13 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 12 14 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 1 1 0 0 20 15 1 1 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 1 0 1 1 1 1 0 1 1 1 0 0 0 18 © 2006 Texas Instruments Inc, Slide 49
  • 50. DSSS – Co-existence Performance • CC2420 - In-band interference • Power of interferer only 1 dB lower than CC2420 transmitter, NO packet errors • Narrowband interferer shown as peak in the centre on top of the CC2420 spread spectrum • A typical FSK receiver requires the desired signal to be 11 dB above interferer © 2006 Texas Instruments Inc, Slide 50
  • 51. Frequency Hopping Spread Spectrum (FHSS) • Signal broadcast over a seemingly random series of frequencies • Receiver hops between frequencies in sync with transmitter • Jamming on one frequency affects only a few bits Power Source: Eliezer & Michael, TI Frequency © 2006 Texas Instruments Inc, Slide 51
  • 52. 2.4 GHz Devices – 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 802.11b/g Microwave Cordless Frequency oven Source: Eliezer & Michael, TI © 2006 Texas Instruments Inc, Slide 52
  • 53. 2.4 GHz – Adaptive Frequency Hopping • Scan the entire frequency band at start-up and restrict usage to frequencies with the lowest energy content. RadioDesk and Bluetooth 1.2 and 2.0 are using AFH. • Substitute frequencies experiencing interference on the fly. Power 802.11b/g microwave cordless Frequency Source: Eliezer & Michael, TI oven © 2006 Texas Instruments Inc, Slide 53
  • 54. 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 1 2 Frequency © 2006 Texas Instruments Inc, Slide 54
  • 55. Agenda • Basics • Basic Building Blocks of an RF System • RF Parameters and RF Measurement Equipment • Support / getting started © 2006 Texas Instruments Inc, Slide 55
  • 56. Getting Started • Define and specify the product Following a standard or going proprietary? Power consumption Range and regulatory requirements – frequency of operation Data rate RF protocol SW content Analyse test tool and instrumentation needs Cost • Compare different vendors – choose RF-IC & tools Purchase and evaluate EVMs and required tools What SW examples, application notes and documentation are available? • Develop, co-operate or outsource? Sufficient resources available? Do you have the necessary competence in-house? Compliance testing? © 2006 Texas Instruments Inc, Slide 56
  • 57. Support • Search for the relevant information Documentation – e.g. data sheets, user guides and application notes Knowledge bases SW examples • Contact your local distributor or TI directly: Internet: TI Low Power Wireless home page: – http://www.ti.com/lpw TI MSP430 home page: – http://www.ti.com/msp430 TI Semiconductor Product Information Center Home Page: – http://support.ti.com TI Semiconductor KnowledgeBase Home Page: – http://support.ti.com/sc/knowledgebase © 2006 Texas Instruments Inc, Slide 57
  • 58. Summary • RF Basics Available frequency bands RF communication systems Modulation and demodulation Basic building blocks of an RF system – components Extending range Key RF parameters RF measurement equipment Spread spectrum systems – DSSS / FHSS / Frequency Agility Getting started Support © 2006 Texas Instruments Inc, Slide 58
  • 59. Thank you for your attention! Questions? SLAP127 © 2006 Texas Instruments Inc, Slide 59
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