Inexpensive modulated backscatter reflector

DETAILED DESCRIPTION The present invention claims an inexpensive modulator for an RFID system for short range applications.
An inexpensive Complementary Metal Oxide Semiconductor (CMOS) gate is used in place of the typically used high quality diode to modulate the reflectivity or impedance of an MBS antenna simplifying the Tag design and significantly reducing cost of manufacture of the Tag and overall system cost.
FIG.
2 shows a block diagram of the present invention, a simple read-only tag, for applications such as tracking airline luggage.
Information such as encoded data stored in the Tag Shift Register 203, is used to drive a Variable Impedance device 202, a CMOS gate in this embodiment, coupled to the Tag Antenna 201.
Other Data Storage devices such as a Read Only Memory (ROM) or similar devices can be used instead of a shift register to drive the Variable Impedance device 202.
Variable Impedance device 202 receives the encoded data and modulates the reflectivity of Antenna 201 in accordance with the encoded data.
The Power Module 204, in this embodiment, is either an inexpensive battery or a rectifier which draws its power from the illuminating RF.
This invention would constitute an important element of a low cost, read-only RFID Tag for short range applications such as airline baggage tracking.
Using a CMOS Gate 202 for this purpose has the advantage over other modulation schemes of low cost and low power usage.
This type of Tag is used for short range applications (less than 2 meters) due to the less efficient Variable Impedance device and, in the case in which the Tag is RF-powered, rapid fall off of RF power with distance from the Interrogator.
The use of an inexpensive CMOS Gate 202 as a modulating element for a Modulated Backscatter RFID Tag such as the one depicted in FIG.
1 will now be described.
FIG.
3 is a block diagram of a simple test circuit which demonstrates how a simple CMOS Inverter Gate 302 can be used as a modulating element in an MBS Tag such as the one depicted in FIG