Telecommunications – Transmitter and receiver at separate stations – Short range rf communication
Reexamination Certificate
1999-07-12
2001-08-07
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at separate stations
Short range rf communication
C455S196100
Reexamination Certificate
active
06272321
ABSTRACT:
The invention relates to a method for calibrating an oscillating receiver circuit of a transponder in an RFID system to resonance to the frequency of an inquiry signal transmitted by a reader, the oscillating receiver circuit comprising at least one inductive resistor and at least one capacitor.
In identifying persons, animals and objects, in recent years a system has proved itself in which a stationary or portable reader supplies a transponder, connected to the object to be identified, with energy via an alternating field, wherein the transponder responds by transmitting the data stored in it. Because of the frequency range used, these are also known as radial frequency identification systems, or RFID for short.
An RFID transponder in general comprises an antenna coil and an integrated circuit, which contains all the necessary electric circuit blocks, for instance for voltage supply, for clock pulse generation, for sequence control, and for storing the data necessary for the identification. The capacitor connected parallel to the antenna coil is also often a component of the integrated circuit. However, it can also be formed by a discrete component.
The RFID reader comprises an oscillating circuit with a transmitting coil and a capacitor, and the circuit is triggered by a driver stage with a signal, generally at a fixed frequency, such as 125 kHz. The reader also includes electronic circuit blocks, for detecting the data sent by the transponder as a result of the absorption modulation, and for sending data and instructions, for instance to modulate the field, to the transponder.
In data or energy transmission, the reader and transponder form a loosely coupled transformer. The energy transmission is therefore relatively slight.
The attainable range for contactless transmission of energy and data is affected by the following peripheral conditions:
transmission energy (limited by regulations set by law)
coil dimensions
ambient noise level
conformance of the resonant frequencies
modulation rise
voltage loss via the rectifier stage
transmission methods employed
So that a voltage sufficient for its operation will be available to the transponder; the oscillating receiver circuit, formed by the antenna coil and the parallelconnected capacitor, should be operated in resonance with the transmission frequency.
Because of tolerances in the components when the transponder is manufactured, this is generally not assured.
The object of the invention is therefore to disclose a method so that during transponder operation, the oscillating receiver circuit will be operated to resonance to the frequency of the inquiry signal.
This object is attained by a method as defined by the characteristics of claim
1
.
A further object is to disclose a circuit arrangement for performing the method.
This object is attained by a circuit arrangement having the characteristics of claim
10
.
The advantageous embodiment of the invention is made in accordance with the characteristics of the dependent claims.
REFERENCES:
patent: 5293400 (1994-03-01), Monod et al.
patent: 5491715 (1996-02-01), Flaxl
patent: 5550536 (1996-08-01), Keine
patent: 5673018 (1997-09-01), Lowe et al.
patent: 44 38 286 (1996-09-01), None
patent: 44 38 287 (1996-09-01), None
Bruhnke Michael
Hirsch Konrad
Melchior Marc
Schülgen Andreas
Cong Le Thanh
Kinberg Robert
Spencer George H.
Temic Semiconductor GmbH
Venable
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