Telecommunications – Transmitter and receiver at separate stations – Short range rf communication
Reexamination Certificate
2000-05-25
2003-06-24
Nguyen, Duc (Department: 2745)
Telecommunications
Transmitter and receiver at separate stations
Short range rf communication
C455S106000, C340S010100
Reexamination Certificate
active
06584301
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to inductive reader devices for use with contactless smartcards, radio frequency identification devices and other transponders, and in particular to an inductive reader device with an integrated antenna and signal coupler.
BACKGROUND OF THE INVENTION
Inductive reader devices are known for use with transponders, such as contactless smartcards and radio frequency identification devices. In radio frequency communication systems employing readers and transponders, the reader typically provides a radio frequency excitation signal. When a transponder is brought in close proximity to the reader device, electromagnetic coupling via the excitation signal powers the transponder and enables the transponder to generate a radio frequency response signal. This response signal is electromagnetically coupled to the reader. A data signal from the transponder included in the response signal is received by the reader and used for processing.
FIG. 1
is a block diagram showing schematically a known inductive reader device
10
. Reader device
10
includes a transmitter
12
, a receiver
14
an antenna
16
and a transformer
18
. Transmitter
12
generates a radio frequency excitation signal using a signal source
20
, which is typically controlled by a control circuit and a modulator that modulate commands onto the excitation signal. Transmitter
12
is directly connected to antenna
16
. Antenna
16
is a coil having a predetermined inductance. Antenna
16
is typically implemented as a coil etched on a printed circuit board. Antenna
16
is generally made to consume as large an area as available in order to improve electromagnetic coupling between the reader device
10
and a transponder. Antenna
16
is directly connected to transformer
18
. Transformer
18
is a discrete component that is separate and apart from antenna
16
. Transformer
18
is connected to receiver
14
. Transformer
18
does not inductively couple to a transponder. Transformer
18
is used to electrically receive from antenna
16
a data component of the modulated response signal returned by a transponder. This signal is then received by the receiver
14
, which is directly connected to the transformer
18
. The received signal is used by the reader circuit in accordance with the application, for example, security identification, smartcard transactions, etc.
One problem with the reader device
10
shown in
FIG. 1
is the use of the discrete transformer
18
. Transformer
18
is physically large and consumes valuable printed circuit board area. Transformer
18
is relatively expensive as well. In addition, some discrete transformer components are prone to failure, impacting the reliability of the product. Also, the characteristics of the transformer are required to be matched to the antenna, which may require custom transformer components for some reader devices.
FIG. 2
shows a known reader device
50
that eliminates the need for a discrete transformer, such as transformer
18
. Reader device
50
includes a transmitter
52
, a receiver
54
, a transmitter antenna
56
and a receiver antenna
58
. Transmitter
52
generates an excitation signal that is emitted by transmitter antenna
56
. Transmitter antenna
56
is a coil. Electromagnetic coupling is used to transmit the excitation signal to a transponder brought in close proximity to transmitter antenna
56
. Rather than receiving the responsive signal from a transponder via the same antenna element, as is the case in reader device
10
, the receiver antenna
58
is provided for coupling to the transponder to receive the responsive radio frequency signal. Receiver antenna
58
is directly connected to receiver
54
to transfer the received responsive signal to the receiver. As illustrated in
FIG. 2
, transmitter antenna
56
and receiver antenna
58
share an available antenna area
60
. The antennas
56
,
58
are implemented as traces in a printed circuit board. The antennas are electrically isolated. The antennas partially overlap each other for mutual flux cancellation, which is required to isolate the transmitter and the receiver for proper circuit operation. Since the antennas must overlap partially, the total antenna area cannot be used for any one antenna. Therefore the size of both antennas is compromised in comparison to the total available antenna area. The reduced antenna area reduces the operating range of the reader device. This may be undesirable, in particular, for small portable reader devices.
Therefore, a need exists for a cost effective reader device with minimal limitations on operating range due to antenna size.
REFERENCES:
patent: 4922261 (1990-05-01), O'Farrell
patent: 5084699 (1992-01-01), DeMichele
patent: 5266926 (1993-11-01), Beigel
patent: 5317330 (1994-05-01), Everett et al.
patent: 6124803 (2000-09-01), Hamma
Bohn Thomas B.
Rachwalski Richard S.
Schamberger Mark A.
Cyrus Khosravi K.
Davis Valerie M.
Motorola Inc.
Nguyen Duc
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