Telecommunications – Transmitter and receiver at separate stations – Short range rf communication
Reexamination Certificate
1999-01-05
2001-08-28
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Transmitter and receiver at separate stations
Short range rf communication
C455S073000, C455S343200
Reexamination Certificate
active
06282407
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to near field wireless communication systems and more particularly to radio frequency identification (RFID) systems and RFID transceivers or transponders.
BACKGROUND OF THE INVENTION
Radio Frequency Identification (RFID) technology allows identification data to be transferred remotely which provides a significant advantage in identifying persons, articles, parcels, and others. In general, to access identification data stored in a RFID transponder (a.k.a. a tag) remotely, a RFID reader generates an energy field to activate the RFID transponder and subsequently to retrieve data stored in the transponder unit from a distance. The data retrieved is then processed by a host computer system to identify the person or article that is associated with the transponder. RFID technology has found a wide range of applications including tracking, access control, theft prevention, security, etc. An example of an application of RFID technology is for article theft prevention in retail stores and libraries.
For some applications, RFID technology is more preferable than magnetic strip technology, which also finds applications in a few of the areas above. The reason is systems employing RFID technology can store a lot more information than magnetic strip technology. Magnetic strip technology as commonly deployed is capable of storing only a few bits of information (e.g., typically indicating whether or not authorization is allowed). Accordingly, magnetic strip technology is not used in applications where data is required to make an identification such as name, date of birth, etc.
RFID technology should be distinguished from Radio ID technology which uses ordinary radio waves, or more precisely far field electromagnetic (EM) waves which are also known as radiation waves. Far field means the distance between the transceiver and transponder is great compared to the wavelength of the electromagnetic carrier signal used. An example of Radio ID technology is the Identify—Friend or Foe (IFF) systems used with military aircraft. Far field electromagnetic waves have a field strength that varies inversely with the distance involved.
In contrast, conventional RFID technology is inductance-based. More precisely, conventional RFID technology uses near field electromagnetic waves which are also known as induction waves. Unlike radio waves, the field strength of induction waves is proportional to the inverse square of the distance involved. In inductance-based RFID technology, an electromagnetic field is generated for use both as a power source for the transponder and for transferring information between the reader and transponder. Inductance waves are generated using closed circuit alternating current coils that have multiple turns. Inductance coils are required to optimally transmit and receive electromagnetic signals are usually a wire wound or etched metal coil. Using inductance coils adversely impacts the costs, manufacturability, and packaging flexibility of inductance-based RFID technology particularly when used with high number of RFID tags usually required in a system. Due to the prohibitive costs and high degree of manufacturing difficulty, electromagnetic RFID technology is not practical in high volume and low cost applications such as in disposable applications. The bulky packaging, which is typical for electromagnetic RFID, further limits its application to those where thickness is not of primary importance.
Traditionally electromagnetic transponders in electromagnetic RFID systems derive their power from the electromagnetic signals being transmitted by an electromagnetic reader through induction coupling and have no power storage device. These electromagnetic transponders are often referred to as passive electromagnetic transponders. Because they require inductive coupling, the distance for communication between an electromagnetic reader and a passive electromagnetic transponder, referred to as the read range, is limited. The read range is limited because a sufficient amount of charge to power up the components within a passive electromagnetic transponder is required and is only available within certain distances from the electromagnetic reader.
Additionally, only certain amounts of power are available for components within a passive electromagnetic transponder. This limited amount of power constrains the choices of components used within a passive electromagnetic transponder. For example amplifiers may be restricted in their power consumption and gain or they may not be used at all within a passive electromagnetic transponder. Additionally certain passive components are often used due to the limited power and take up larger amounts of space than otherwise might be required. Furthermore the limited of amount of available power in a passive electromagnetic transponder reduces the available functionality and operation of a transponder.
Additionally when using passive electromagnetic transponders, the electromagnetic readers are required to generate very high electromagnetic field strengths in order to achieve an adequate operating range. Oftentimes when generating these high electromagnetic field strengths electromagnetic interference (EMI) occurs to other radio frequency devices that may be communicating near by. Noise tends to cause problems in low power signals that a passive electromagnetic transponder generates. Furthermore, receiver technology within an electromagnetic reader can not be as sensitive as it otherwise might be due to noise sources that surround transmission of signals to the passive technology employed in the passive electromagnetic transponder.
In certain applications it is desirable to have an RFID communication system with larger read range than available with passive electromagnetic transponders. Typical read range for passive electromagnetic transponders is on the order of four inches to thirty inches. An exemplary application for larger read range is a ticket admittance system. It may be desirable to have a reader be quite a distance away, such as five to eight feet, when a ticket holder passes through an entrance of the ticket admittance system. In cases such as this, it is difficult to bring an electromagnetic transponder within the passive read range.
Thus it is desirable to have an apparatus, system and method for increasing the read range for an RFID communication system. It is desirable to increase the choices of components available for use in an RFID transponder. It is desirable to further integrate components of an RFID transponder such that manufacturing costs are lowered. Additionally, it is desirable to increase the operational functionality of RFID transponders. It is desirable to reduce interference within an RFID communication system so that more sensitive receivers in an RFID reader may be developed. Additionally, it is desirable to introduce an RFID apparatus, system, and method that is cost-effective, has high manufacturability, and can be easily packaged for a wide range of applications including a disposable RFID tag or transponder.
BRIEF SUMMARY OF THE INVENTION
Briefly, an active electrostatic transceiver is provided that has electrostatic electrodes, an energy storage means such as a battery and a transceiver circuit for communication within an electrostatic RFID communication system. The transceiver circuit includes power management features so that the energy storage means is not quickly depleted. Additionally the transceiver circuit includes amplifiers and filters so that the read range is further increased and noise filtering is improved. In a first embodiment, the transceiver circuit has a clock extractor that extracts a clock from the incoming data signal such that the clock and the data signal are synchronized so that demodulating the data from the data signal is simplified. In a second embodiment, the transceiver circuit has its own clock generator for initiating transmission of signals so that a reader need not have an exciter to generate an excitation signal. Both embodiments of the transceiver
Rolin John Howard
Vega Victor Allen
Bhattacharya Sam
Eisenzopf Reinhard J.
Hughes Terri S.
Motorola Inc.
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