Demodulators – Frequency modulation demodulator – Input signal converted to and processed in pulse form
Reexamination Certificate
1999-02-26
2001-09-25
Kinkead, Arnold (Department: 2817)
Demodulators
Frequency modulation demodulator
Input signal converted to and processed in pulse form
C340S010100, C340S010520, C340S010340, C340S572100, C342S042000, C342S051000, C329S341000, C455S343200
Reexamination Certificate
active
06294953
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to radio frequency identification (RFID) systems and more particularly to a high sensitivity demodulator for a radio tag and method.
BACKGROUND OF THE INVENTION
The management and tracking of personnel, assets, and other objects is required in a wide variety of environments and is often cumbersome, labor intensive, and expensive. Radio receivers and transmitters have been used for many years to identify personnel and objects in such environments. For example, many systems are known for attaching radio tags to items, such as automobiles, so that when automobiles equipped with radio tags enter a certain area, such as a toll booth area, the automobiles are automatically identified and the appropriate tolls are deducted from corresponding accounts, thereby obviating the need for drivers to stop and make payment at toll booths. Innumerable other applications for such radio tag systems have been identified, in areas ranging from inventory control to facility security to sporting event timing.
Radio frequency identification (RFID) systems generally use a fixed position base station capable of reading remote, portable tags attached to personnel, assets, or other objects. Tags generally operate on their wake-up frequency at low frequency, very low frequency, or microwave bands. Because of power consumption concerns and the life span of the portable, remote radio tags operating at low frequency or very low frequency, exclusive OR (“XOR”) gates are almost exclusively used to demodulate incoming radio frequency signals. The use of XOR gates leads to low sensitivity and limited operational range for the radio tags.
SUMMARY OF THE INVENTION
In accordance with the present invention, a high sensitivity demodulator for a radio tag and method is provided which substantially eliminates or reduces disadvantages and problems associated with conventional demodulators for radio tags.
According to one embodiment of the present invention, there is provided a radio frequency tag comprising a threshold voltage generator and a comparator for demodulating a received signal. The threshold voltage generator generates a threshold voltage signal and forwards that signal to a first comparator input. An antenna receives a signal and forwards that received signal to a second comparator input. The comparator generates a digital output signal based on the results of the comparison of the two inputs.
More particularly, in accordance with a particular embodiment of the present invention, the threshold voltage generator and comparator are powered by only leakage current from a local power supply. The threshold voltage generator is comprised of a first resistor and a second resistor connected in series between the local power supply and a ground. A threshold voltage generator output is connected to the junction between the first resistor and the second resistor to provide the threshold voltage signal to the comparator.
Technical advantages of the present invention include providing an improved radio tag. In particular, the radio tag utilizes a highly efficient comparator that can demodulate low powered analog carrier signals while drawing only minimal current. As a result of the ability to demodulate low powered signals, the radio tag has improved sensitivity and the operational range of the radio tag is significantly increased. In addition, power consumption is minimized to maintain long tag life.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.
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Axcess Inc.
Baker & Botts L.L.P.
Kinkead Arnold
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