1. Modulation and Data Transfer February 21, 2002

2. References http://www.technovelgy.com/ct/Technolo gy-Article.asp?ArtNum=2 http://www.technovelgy.com/ct/Technolo gy-Article.asp?ArtNum=2 http://electronics.howstuffworks.com/sm art-label1.htm http://electronics.howstuffworks.com/sm art-label1.htm http://www.answers.com/topic/iso-15693 http://focus.ti.com/docs/prod/folders/print /ri-i02-114a-01.html#technicaldocuments http://focus.ti.com/docs/prod/folders/print /ri-i02-114a-01.html#technicaldocuments

3. Reader The scanning antenna transmits radio- frequency signals in a relatively short range. It provides a means of communicating with the transponder or the RFID tag. For passive tags it provides the RFID tag with the energy to communicate.

4. Modulation (from Wikipedia) … the process of varying a periodic waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and pitch. Normally a high-frequency sinusoid waveform is used as carrier signal. The three key parameters of a sine wave are its amplitude ("volume"), its phase ("timing") and its frequency ("pitch"), all of which can be modified in accordance with a low frequency information signal to obtain the modulated signal.

5. Reader (or Interrogator) modulates

6. ISO 15693 Smart Tags Inductively coupled EPC GEN2 standard uses ISO 15693 IDs Uses ASK from Reader to Tag Uses ASK or FSK from Tag to Reader Two encoding methods: 1 of 4 and 1 of 256

7. Amplitude Shift Keying - ASK Sends digital data across analog carrier by changing the amplitude of a carrier signal in time with data video

8. Frequency Shift Keying - ASK Sends digital data across analog carrier by changing the frequency of a carrier signal in time with data video

9. Encoding How the tag and reader will interpret the analog carrier to represent digital data. Think Morse code…

10. 1 of 256

11. Data Transmission ASK 0 8 pulses of 423,75 kHz unmodulated time of 18,88 µs (256/ fc 1 unmodulated time of 18,88 µs (256/ fc 8 pulses of 423,75 kHz FSK 0 8 pulses of 423,75 kHz 9 pulses of 484,28 kHz 1 9 pulses of 484,28 kHz 8 pulses of 423,75 kHz

12. Data Transmission to Reader ASK SOF an unmodulated time of 56,64 µs (768/ fc), 24 pulses of 423,75 kHz a logic 1 Data encoded in using Manchester code EOF a logic 0 24 pulses of 423,75 kHz an unmodulated time of 56,64 µs FSK SOF 27 pulses of 484,28 kHz 24 pulses of 423,75 kHz a logic 1 Data encoded in using Manchester code EOF A logic 0 24 pulses of 423,75 kHz 27 pulses of 484,28 kHz

13. Manchester Code

14. Data Transmission to Card Data encoded in using 1 of 4 or 1 of 256 pulse position modulation (PPM) PPM is signal modulation in which M message bits are encoded by transmitting a single pulse in one of 2M possible time-shifts. This is repeated every T seconds Transmitted bit rate is M/T bits per second

15. 1 of 256 Values from 0-255 are encoded by the timing of a pulse 512 timing slots per frame where a pulse may occur Value, v, is encoded by 2*v + 1 = slot location Example: value 24 would be in slot location 49

16. 1 of 4 How many slots per frame? How many bits transmitted per frame?