RIFID TAGS AND METHODS OF DESIGNING RFID TAGS
RFID tags and methods of designing RFID tags. At least some of the illustrative embodiments are RFID tags comprising a tag antenna, a matching circuit coupled to the tag antenna, a shorting device coupled to the tag antenna and the matching circuit (wherein the shorting device is configured to selectively couple the tag antenna to common), and a tag circuit coupled to the matching circuit and the shorting device (the tag circuit configured to control the shorting device). In one or more such embodiments, a difference between a reflection coefficient of the tag antenna when the shorting device is conductive and a reflection coefficient of the tag antenna when shorting device is non-conductive is greater than or equal to approximately 0.8.
1 . A radio frequency identification (RFID) tag comprising:
a tag antenna;
a matching circuit coupled to the tag antenna;
a shorting device coupled to the tag antenna and the matching circuit, wherein conductivity of the shorting device affects a reflection coefficient of the tag antenna; and
a tag circuit coupled to the matching circuit and the shorting device, the tag circuit configured to control the shorting device;
wherein a difference between a reflection coefficient of the tag antenna when the shorting device is conductive and a reflection coefficient of the tag antenna when the shorting device is non-conductive is greater than or equal to approximately 0.8.
2 . The RFID tag according to claim 1 wherein the difference is greater than or equal to 0.9.
3 . The RFID tag according to claim 1 wherein the shorting device further comprises a field effect transistor (FET).
4 . The RFID tag according to claim 3 wherein the FET is engages a same substrate as the matching circuit.
5 . The RFID tag according to claim 3 wherein the shorting device comprises a plurality of FETs in parallel.
6 . The RFID tag according to claim 1 wherein the shorting device further comprises a junction transistor.
7 . The RFID tag according to claim 6 wherein the junction transistor engages the same substrate as the matching circuit.
8 . The RFID tag according to claim 6 wherein the shorting device comprises a plurality of junction transistors in parallel.
9 . The RFID tag according to claim 1 further comprising a power source coupled to the tag circuit.
10 . A radio frequency identification (RFID) tag comprising:
a tag antenna;
a matching circuit coupled to the tag antenna;
a tag circuit coupled to the tag antenna through the matching circuit; and
a switch configured to selectively couple the tag antenna to a common potential;
wherein an impedance of the antenna is more than approximately four (4) times a conducting impedance of the switch.
11 . The RFID tag according to claim 10 wherein the antenna impedance is more than approximately six (6) times the conducting impedance of the switch.
12 . The RFID tag according to claim 10 wherein the antenna impedance is more than approximately eight (8) times the conducting impedance of the switch.
13 . The RFID tag according to claim 10 wherein the matching circuit, tag circuit and switch engage a same substrate.
14 . The RFID tag according to claim 10 wherein the matching circuit and tag circuit engage the same substrate.
15 . The RFID tag according to claim 10 wherein the switch further comprises a plurality of switches coupled in parallel.
16 . The RFID tag according to claim 10 wherein the switch is one or more selected from the group consisting of: a field effect transistor; a junction transistor; a TRIAC; and a Varactor diode.
17 . A method comprising:
designing an antenna for a radio frequency transceiver, wherein physical characteristics of the antenna are selected independent of effects of the physical characteristic on impedance of the antenna; and then
designing an impedance matching circuit having approximately the same impedance as the antenna; and
selecting a shorting device with a conductive impedance, the shorting device selected based on the impedance of the antenna.
18 . The method according to claim 17 wherein selecting further comprising selecting a shorting device whose conductive impedance is less than one quarter (¼) of the impedance of the antenna.
19 . The method according to claim 17 wherein designing the impedance matching circuit and selecting further comprises designing the impedance matching circuit and shorting device to be on the same substrate.
20 . The method according to claim 17 wherein designing the antenna further comprises designing an antenna whose impedance is greater than 100 Ohms.
21 . The method according to claim 17 wherein designing the antenna further comprises designing an antenna whose impedance is greater than 200 Ohms.