UHF RFID Reader Design

Transcription

1 IOT - Basics from the Expert EASP1 Design Case UHF RFID Reader Design Prof. Roland Küng, 2016

2 2004 The Big Bang of Internet of Things The Electronic Product Code (EPC) EPC provides unique* numbering scheme for physical objects EPC is only an ID, the information is stored on the network 96 bit = different codes - Age of earth is s - Diameter of universe is cm ID s available per person in this world - Total capacity of chip manufacturers is tags/year * Uniqueness by EPC and data behind in EPCIS kunr1-2

3 Possible Classification of RFID RuBee NFC BTLE ZigBee WLAN Semi-passive Semi-passive Semi-passive Semi-active passive passive passive active Inductive LF Inductive RF UHF & µwave RFID kunr1-3

4 Different Frequencies in Use kunr1-4 kunr1-4

5 IOT Simple passive UID Tag kunr1-5

6 Tag Zoo kunr1-6

7 Example of Passive Tag kunr1-7

8 IOT Semi-passive Sensors µc Memory Sensor kunr1-8

9 Example of Semi-passive Sensor Rechargeable Battery Sensor Part Antenna Passive RFID kunr kunr1-9

10 Passive UHF RFID Link Budget: - Read Tags up to 8m Distance - Limited by Tag Power Consumption Pt Gt Gr λ Pr = 2 2 (4π) d L 2 * EPC Class 1 Gen dbm - 16 dbm received at tag * S/N = 35 db + 33 dbm (2 W) Path Loss 49 8 m Gain = 7 db Receiver Noise: -99 dbm (F = 25 db, B = 100 khz) - 71 dbm (0.1 nw) Path Loss 49 8 m -22 dbm (6 µw) backscatter signal Reality: Additionally orientation losses, system losses, fading, n > 2... Additional noise sources, amplitude phase, TX to RX coupling kunr1-10

11 RFID EPC Gen2 UHF Reader 10 mm TX antenna modulation switch power amp RX antenna RADIATING signal processor synthesizer I Q 120 mm D A filter direct conversion receiver Passive Tag (Etikette) Reader (Lesegerät) kunr1-11

12 RFID: 4 Watt EPC Gen2 Reader Software Defined Radio (SDR) Architektur DSP FPGA ADC DAC Synthesizer Xscale DC-RX TX Amp Supply Circulator Ethernet USB RS232 4 Antenna Ports kunr1-12

13 SDR: UHF RFID Reader RISC Processor - MAC - Reader Protocol - Interfaces Signal Processing - Sample Level on FPGA - Symbol Level on DSP - Air Protocol on DSP UHF Frontend - Direct Conversion Receiver - Carrier Suppression - Multi Antenna kunr1-13

14 Tag to Reader: Sub Carrier Encoding ASK or PSK modulation: 5 kbps < data rate < 640 kbps Baseband-FM0 for single reader per frequency channel saves bandwidth Miller sub carrier encoding for dense reader environment no reader - tag collisions if massive filtering is used + FM0 Interrogator commanding Interrogator listening Filter Miller Tag response Frequency kunr1-14

15 European Regulatory ETSI Channel BW = 200 khz 4 high power channels allowed within EU, ERP 4 W each Concurrent operation in close proximity of readers on same channel needed kunr1-15

16 Example: Dock Door Application Reader related risks Mutual interference among readers: Co-channel interference Adjacent channel interferences Multi Carrier and Miller Coding Organize frequency plan D = 4 m adjacent interferer distance D = 9 m co-channel interferer distance Nr. 7 an d 13 assumed to be blocked by interferer kunr1-16

17 Example: Dock Door Application Metro Germany Logistic Centre Swiss Post Härkingen Metro RFID Dock Door Portal Swiss Post Härkingen kunr1-17

18 Filtering UHF RFID Reader (Europe) Interrogator commanding Interrogator listening HP Filter Filter LP Tag response -240 khz DC 240 khz ± 80 ± 80 Frequency EPC Gen2/ Europe: Subcarrier and data rates are extremely variable! kunr1-18

19 Interfering Power Levels Interferer has advantage over victim tag because its signal decreases with 1/d 2 versus 1/d 4 of the passive tag P Rx,dBm = P EIRP,dBm + G Rx, dbi + 20 log 4 λ π D First Spec Assumption: Adj. carrier level = weakest tag level fp = 320 khz, Ap = 3 db fs = 600 khz, As = 62 db 7 th order CH plus HP 2.O. against DC from own carrier kunr1-19

20 1 st idea: Integrated Active Filter I-,Q-Filter: N = 6, Butterworth unfortunately above 1 MHz Attenuation unsufficient IM3 spectral lines too high, as IM is generated mainly by interferers kunr1-20

21 What s Possible 2017: ADRF6518 Matched pair of programmable filters Continuous gain control range: 72 db Digital gain control: 30 db Filter bypass mode bandwidth (BW) 3 db small signal bandwidth: 1100 MHz, VGA2 and VGA3 21 db/12 db 6-pole Butterworth filter: 1 MHz to 63 MHz in 1 MHz steps, 0.5 db corner frequency IMD3: >65 dbc for 1.5 V p-p output

22 I-/Q- Basisband Filter 2 nd idea: Active RC failed due to GBP (Qmax 320 khz) I IN I OUT 3 rd idea: LC Filter Design selected Noise free No IM 7. Order LP 3 db Chebishev f c = 320 khz Q Q kunr1-22

23 I-/Q- Basisband Filter Carrier CH1 Tag Carrier CH2 LP Design shows most hardest Spec kunr1-23

24 Modern Characterization of ADC: Dynamic Range, Spurious ADC Speed and power constraints: 14 Bit ADC 5 Msps Fading Marge 10 db Max input level: -10 dbfs Tag signal dynamic range: 40 db Nr.of Bits for Min input level: 4 Bit Spurious min 10 db lower -10 dbfs Tag Dynamic Range 40 db SFDR -84 dbfs Min SNR 4 Bit -50 dbfs -74 dbfs kunr1-24

25 Selected ADC SNR SFDR Integrated dual 14-bit ADC Single 3 V supply operation (2.7 V to 3.6 V) SNR = 74 db (to Nyquist, AD ) SFDR = 86 dbc (to Nyquist, AD ) Low power: 90 mw/channel at 20 MSPS Nyquist Example: fs = 5 Msps, FFT 16k-point no averaging kunr1-25

26 Modern Characterization of ADC: Noise Floor ADC DAC SNR Noise Density [dbc/hz]: Measured Value - 10 log (BW) Noise für SNR: Noise Density + 10 log(f s /2) Noise Density [dbc/hz]: FFT Floor 10 log (f s /M) kunr1-26

27 Synthesizer for European (868 MHz, 4 channels) and US Regulations ( MHz) PLL: Modulus Divider Phase/Frequency Detector Charge Pump VCO MHZ Clock Buffer TCXO 20 MHz Loop Filter 3. Ordnung B = 4 khz kunr1-27

28 I/Q - Downconversion MAMXSS0011 uses FET Switch for mixing High IIP3: 20 dbm I Mixer 90 0 Phase Shifter Q Mixer 3 db Power Splitter Interrogator commanding Interrogator listening Filter Mixes the User Carrier In CHx to DC Tag response DC Frequency kunr1-28

29 Further Challenges for Reader Tag response in Dense Reader Mode is received in channel adjacent to carrier While transmitting, readers are emitting noise to this adjacent channels where the tag response is received Noise from several modulated readers sum up and interfere with weak tag responses Min. distance d between co-channel operated readers must be respected Lit.: ETSI EN V1.2.1 kunr1-29

30 UHF Signal Propagation Material Orientation Test fixture with 7 3 Gen2 tags, equally spaced in air medium Target read time: < 1 second kunr1-30

31 UHF Signal Propagation Multi-path reflections from metal (reinforcing in floors/ dock levellers and other objects), cause nulls and peaks that get worse with distance from the antenna. height Reader -3 dbm -14 dbm kunr1-31

32 λ π π λ = d h h 2 sin d ) (4 G G P 4 P r t r t t r Fading - Problem in Passive RFID Simple 2-Ray Model RFID: Carrier only Slow Flat Fading Channel kunr1-32