Radio Frequency Identification

Transcription

1 Radio Frequency Identification Retail item level Radio Frequency Tagging Market size: >1 Trillion die/year (Retail, item tags)

2 Economic impact 5% of sales lost due to not on shelf 5-15% of some items stolen Grey market tracing Pharmaceuticals counterfeit, liability, recall, expiration Item tracking and locating

3 Packaging technology

4 RFID An RFID device typically has a single two terminal VLSI CMOS chip and a printed antenna on a flexible substrate. The RF at the terminals is rectified, multiplied. An on chip PLL locks to transmitted modulation The AM incoming modulation is decoded A response is transmitted by modulating the reflection of the tag Thousands of tags may be powered at once, so a protocol is used to specify which tag is to respond Tags have 128 or more bits of on chip E 2 memory for the identifier.

5 Beam power Low frequency tags are powered by induction, not transmission. Range < 2 meters High frequency tags are almost always limited by voltage, not power. Typical power threshold 25 microwatts Need.5 volts to turn on best nonlinear devices: Shottkey diodes. Lower power unloads Shottkeys and increases voltages, but effect not important at about 10 microwatts. Voltage multipliers High radiation resistance antennas

6 Antenna Impedance For good antennas, power into a matched load is independent of impedance Higher impedance antennas give higher voltages The chip s input impedance is dominated by about 1 pf of capacitance at UHF, so need to provide low loss inductive loop to resonate Q~10 for bandwidth (Europe to Japan)

7 Available tag power and voltage (905 Mhz) Power received by matched load Radiation Resistance Range m mw Open circuit voltage

8 How do you talk to 1000 s of tags at a time? TTF (Tags talk first) em Marin Deterministic tree walk (bit wide) epc Class 0 Query-Response Deterministic multi-bin epc Class 1 Pseudorandom multi-bin ISO Aloha Random single response Q Ready-Quiet single state bit, through power drop out

9 Deterministic, Tree walking bit wide (class 0)

10 Bit wide interleave

11 AutoID center class 1 spec Stateless protocol Each command atomic Simple and robust recovery from errors and dropouts Tag backscatter reply during reader CW Reduces RF noise from readers Uses only a single channel in band Wirelessly Programmable tags Prevents tag inventory nightmare Allows consistent epc coding

12 3 bit tree walk Query Query

13 Q state diagram A SetState commands SetState commands B QueryA Any but ACK Any but ACK QueryB Waiting for ACK NAK (Any New Query) NAK Waiting for ACK ACK ACK Waiting for new Query, Select or NAK Waiting for new Query, Select or NAK Select Select Selected ProgramID, LockID, (class 2) Read or Write Selected ProgramID, LockID. (Class 2) Read or Write KILL KILL X X DEAD

14 Frequency considerations Efficient antennas are approximately ½ wavelength long At 900 Mhz, that translates to > 10 cm with capacitive loading Max power available into a matched load scales with wavelength squared Range at 2.4 GHz around a meter for beam powered devices

15 RF issues Tags are interrogated on a single frequency, so can find lucky frequency which can penetrate and power tags in difficult environments. High tag count rate allows longer silent intervals for other uses. What is next to the tag can shift the tags resonance frequency considerably

16 Synchronization Tags can not distinguish absolute time (no crystal, process variations) Tags look for modulated power only, limited only by antenna resonance. Tags look for patterns in relative modulation lengths to determine encoding All timing based on PLL to incoming signal

17 Backscatter Uplink Backscatter: antenna load is rapidly changed, resulting in modulation of scattered radiation Minimal power required ( <5 microwatts) Return signal is RF synchronous with transmitter, allowing robust Hetrodyne reception giving surprisingly large range ( > 8 meters demonstrated)

18 Uplink modulation Timing derived from downlink Use invertible modulation scheme Two channels in quatrature so one channel is in phase

19 RF regulations (frequency) Most bands are licensed, and are allocated to specific users Unlicensed RFID only possible by part 15, in a few bands: MHz, 2.4 GHz In Europe, only single frequency 869MHz In Japan, only 2.4 GHz available

20 Fabricate elements: Micromachining +/- 2 micron

21 Facet selective etching

22 De vic e Substra te Me tal Layer Pla narizing Layer MOS Circ uitry Fluidic Self Assembly Efficient use of source material and target site area. Cost is proportional to area. Much smaller die sizes and interconnect parasitics than flip-chip bonding. Process steps are completely separate Planar interconnects.

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24 Nanochips and Ant Photo by Ron Wilson

25 Q Protocol Query[Q] < Probability[(1/2)^Q] > tag response [16 random bits] ACK[handshake same 16 bits] tag response[id&crc] Symmetrical A B, no unselected state Based on a single bit coin toss true random number generator

26 Q state diagram A SetState commands SetState commands B QueryA Any but ACK Any but ACK QueryB Waiting for ACK NAK (Any New Query) NAK Waiting for ACK ACK ACK Waiting for new Query, Select or NAK Waiting for new Query, Select or NAK Select Select Selected ProgramID, LockID, (class 2) Read or Write Selected ProgramID, LockID. (Class 2) Read or Write KILL KILL X X DEAD

27 Performance Short coherence time No choke point (N log N) R T bits per tag inventoried (typical) Prefix+CRC+ePC T R bits per tag inventoried (average) Tag bits concealed from reader emissions Capable of Simultaneous multireader operation(when set to complete atomicity and Query-ACK commands grouped) These results assume a relatively short coherence time is required, but not complete atomicity. Hidden collisions will improve statistics. (Weak tags are protected by the ACK handshake, and the stronger tag is still counted if its handshake can be extracted by the reader) no response, collision

28 Features Four total independent sessions (simultaneous multireader) Match/not match masking independent in each session masking (tag set U ~, etc.) Unmasked latecomers included or excluded in masked session (either possible).

29 RF link Split phase Manchester forward link, with low jitter falling edges, 30% minimum modulation depth Duty cycle 50%-75% Minimum low time 3 microseconds Selectable backscatter multiple (1x,2x, 4x)(T->R relative) Selectable backscatter modes Forward rate kbps

30 Five sorting commands QueryA QueryB QueryRep ACK NAK

31 This is the reader flow chart for counting Tags. Query ( Q,A/B, Session) or QueryRep The reader would start in the A inventory mode, at the top of the flow chart. Legible 16 bit response? The probability of a tag responding to a query is (1/2)^Q The reader would adjust its Q parameter to keep roughly the same number of empty, full, and collided bins The reader would continue to run this procedure, adjusting Q continuously, until no further tags respond, with Q=0. At this point, all reachable tags are in the B state. Then it would go to an B inventory and do it again, putting all tags back in the A state. Yes ACK (same 16 bits) Legible CRC and epc? No Try ACK again? No NAK