Patent Application
20080062046
For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings.
The following description is the best mode presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.
Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and as defined in dictionaries, treatises, etc.
The use of RFID tags are quickly gaining popularity for use in the monitoring and tracking of an item. RFID technology allows a user to remotely store and retrieve data in connection with an item utilizing a small, unobtrusive tag. As an RFID tag operates in the radio frequency (RF) portion of the electromagnetic spectrum, an electromagnetic or electrostatic coupling can occur between an RFID tag affixed to an item and an RFID tag reader. This coupling is advantageous, as it precludes the need for a direct contact or line of sight connection between the tag and the reader.
Utilizing an RFID tag, an item may be tagged at a period when the initial properties of the item are known. For example, this first tagging of the item may correspond with the beginning of the manufacturing process, or may occur as an item is first packaged for delivery. Electronically tagging the item allows for subsequent electronic exchanges of information between the tagged item and a user, wherein a user may read information stored within the tag and may additionally write information to the tag.
As shown in
The EPC is a simple, compact identifier that uniquely identifies objects (items, cases, pallets, locations, etc.) in the supply chain. The EPC is built around a basic hierarchial idea that can be used to express a wide variety of different, existing numbering systems, like the EAN.UCC System Keys, UID, VIN, and other numbering systems. Like many current numbering schemes used in commerce, the EPC is divided into numbers that identify the manufacturer and product type. In addition, the EPC uses an extra set of digits, a serial number, to identify unique items. A typical EPC number contains:
Each tag 102 may also store information about the item to which coupled, including but not limited to a name or type of item, serial number of the item, date of manufacture, place of manufacture, owner identification, origin and/or destination information, expiration date, composition, information relating to or assigned by governmental agencies and regulations, etc. Furthermore, data relating to an item can be stored in one or more databases linked to the RFID tag. These databases do not reside on the tag, but rather are linked to the tag through a unique identifier(s) or reference key(s).
Communication begins with a reader 104 sending out signals via radio wave to find a tag 102. When the radio wave hits the tag 102 and the tag 102 recognizes and responds to the read's signal, the reader 104 decodes the data programmed into the tag 102. The information is then passed to a server 106 for processing, storage, and/or propagation to another computing device. By tagging a variety of items, information about the nature and location of goods can be known instantly and automatically.
Many RFID systems use reflected or “backscattered” radio frequency (RF) waves to transmit information from the tag 102 to the reader 104. Since passive (Class-1 and Class-2) tags get all of their power from the read signal, the tags are only powered when in the beam of the reader 104.
The Auto ID Center EPC-Compliant tag classes are set forth below:
Class-1
Class-2
Class-3
Class-4
In RFID systems where passive receivers (i.e., Class-1 and Class-2 tags) are able to capture enough energy from the transmitted RF to power the device, no batteries are necessary. In systems where distance prevents powering a device in this manner, an alternative power source must be used. For these “alternate” systems (also known as semi-active or semi-passive), batteries are the most common form of power. This greatly increases read range, and the reliability of tag reads, because the tag does not need power from the read to respond. Class-3 tags only need a 5 mV signal from the reader in comparison to the 500 mV that Class-1 and Class-2 tags typically need to operate. This 100:1 reduction in power requirement along with the reader's ability to sense a very small backscattered signal enables the tag permits Class-3 tags to operate out to a free space distance of 100 meters or more compared with a Class-1 range of only about 3 meters. Note that semi-passive and active tags with build in passive mode may also operate in passive mode, using only energy captured from an incoming RF signal to operate and respond.
Active, semi-passive and passive RFID tags may operate within various regions of the radio frequency spectrum. Low-frequency (30 KHz to 500 KHz) tags have low system costs and are limited to short reading ranges. Low frequency tags may be used in security access and animal identification applications for example. Ultra high-frequency (860 MHz to 960 MHz and 2.4 GHz to 2.5 GHz) tags offer increased read ranges and high reading speeds. One illustrative application of ultra high-frequency tags is automated toll collection on highways and interstates.
Embodiments of the present invention are preferably implemented in a Class-3 or higher Class chip, which typically contains the control circuitry for most if not all tag operations.
A battery activation circuit 214 is also present to act as a wake-up trigger. In brief, many portions of the chip 200 remain in hibernate state during periods of inactivity. A hibernate state may mean a low power state, or a no power state. The battery activation circuit 214 remains active and processes incoming signals to determine whether any of the signals contain an activate command. If one signal does contain a valid activate command, additional portions of the chip 200 are wakened from the hibernate state, and communication with the read can commence. In one embodiment, the battery activation circuit 214 includes an ultra-low-power, narrow-bandwidth preamplifier with an ultra low power static current drain. The battery activation circuit 214 also includes a self-clocking interrupt circuit and uses an innovative user-programmable digital wake-up code. The battery activation circuit 214 draws less power during its sleeping state and is much better protected against both accidental and malicious false wake-up trigger events that otherwise would lead to pre-mature exhaustion of the Class-3 tag battery 210.
A battery monitor 215 can be provided to monitor power usage in the device. The information collected can then be used to estimate a useful remaining life of the battery.
A forward link AM decoder 216 uses a simplified phase-lock-loop oscillator that requires an absolute minimum amount of chip area. Preferably, the circuit 216 requires only a minimum string of reference pulses.
A backscatter modulator block 218 preferably increases the backscatter modulation depth to more than 50%.
A memory cell, e.g., EEPROM, is also present. In one embodiment, a pure, Fowler-Nordheim direct-tunneling-through-oxide mechanism 220 is present to reduce both the WRITE and ERASE currents to about 2 μA/cell in the EEPROM memory array. Unlike any RFID tags built to date, this will permit designing of tags to operate at maximum range even when WRITE and ERASE operations are being performed. In other embodiments, the WRITE and ERASE currents may be higher or lower, depending on the type of memory used and its requirements.
The module 200 may also incorporate a highly-simplified, yet very effective, security encryption circuit 222. Other security schemes, secret handshakes with readers, etc. can be used.
Only six connection pads (not shown) are required for the illustrative chip 200 of
It should be kept in mind that the present invention can be implemented using any type of tag, and the circuit 200 described above is presented as only one possible implementation.
Many types of devices can take advantage of the embodiments disclosed herein, including but not limited to RFID systems and other wireless devices/systems. To provide a context, and to aid in understanding the embodiments of the invention, much of the present description has been presented in terms of an RFID system such as that shown in
As mentioned above, it is desirable to match a circuit of an RF device to the antenna. Such matching provides maximum signal, maximum data transfer rate, stable operation, etc. Accordingly, one embodiment of the present invention is an RFID device such as an RF tag that includes an antenna, an integrated circuit, and a structure positioned between the antenna and the integrated circuit for electrically coupling the antenna to the integrated circuit, the structure assisting in matching RF-related properties of the integrated circuit and the antenna.
The subassembly of the structure 302 and integrated circuit 200 is coupled to a base circuit substrate to form the device 102. In a preferred embodiment, the subassembly is adhered to a thin metallic film antenna 304 to form an RFID tag. The antenna 304 (or a similar circuit made from metallized film or other metallized flex circuit) can be made from a thin etched or stamped foil, typically manufactured from a thin foil of copper, copper-alloy, or nickel-iron alloy by stamping or etching. The etching or stamping creates patterns on strips that become antennas. Other methods of making an antenna include printing a conductive ink.
Any suitable mode of coupling the various components together is acceptable, including soldering, use of anisotropically conductive pressure sensitive adhesive, etc. A pressure sensitive conductive adhesive is preferred for attachment of the structure 302 to the antenna 304 or similar circuit, and a different adhesive can be used to attach the integrated circuit 200 to the structure 302, such as a conductive hot melt.
Again, the structure 302 assists in matching RF-related properties of the integrated circuit 200 and the antenna 304. Such properties may include one or more of impedance, conductance and capacitance. The structure may also provide transmission line matching, among other types.
In one embodiment, the structure may assist in matching the antenna inputs 306 of the integrated circuit 200 and the antenna 304 due to a particular shape of its traces, material(s) of construction, presence of analog components, or combination thereof.
In another embodiment, the structure may create or simulate inductance to compensate for capacitance of the integrated circuit due to a particular shape of its traces, material(s) of construction, presence of analog components, or combination thereof. For instance, the antenna has very little impedance while the impedance on the integrated circuit chip is primarily capacitive. The structure may compensate for this via an inductor, materials of construction, etc.
In yet another embodiment, if a response would otherwise drift in one direction, the structure stabilizes the drift.
Because the structure described herein provides stable matching between the integrated circuit and the antenna, antenna design may be greatly simplified. Particularly, matching considerations may be significantly removed from antenna build. For instance, the antenna does not need to have a complex design to provide impedance matching, and so design time is reduced. Also, the antenna may be constructed of very inexpensive materials, thereby significantly reducing the overall cost of the device. Further, the structure provides wider tolerances for antenna manufacturing variations, which also reduces fabrication costs.
The base of the structure in any of these embodiments is preferably constructed of a dielectric material, ideally a controlled dielectric material. As known to those skilled in the art, controlled dielectric materials are very expensive. However, the controlled dielectric materials are much more stable in varying environmental conditions, and even exhibits fewer manufacturing variations. Thus, because high quality materials need only be used in the structure and not the antenna, the structure may be of small dimensions relative to the tag as a whole, the benefits provided by the increased stability and matching typically outweigh the cost detriment.
Similarly, the traces are preferably constructed of a high quality material, for similar reasons.
The structure 302 is ideally as small as possible such as 1 inch square or less. The structure 302 preferably has a geometric shape, such as a rectangle or square, that allows for ease of manufacture and assembly.
The structure may include a circuit that assist in the matching. For example, such circuitry may include one or more capacitors, resistors, inductors, etc.
Note that the structure does not need to be configured as an interposer, but rather could surround the integrated circuit, lie along one side thereof, etc.
One skilled in the art will appreciate how the systems and methods presented herein can be applied to a plethora of scenarios and venues, including but not limited to automotive yards, warehouses, construction yards, retail stores, boxcars and trailers, etc. Accordingly, it should be understood that the systems and methods disclosed herein may be used with objects of any type and quantity.
While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
