Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1999-10-29
2002-10-08
Pope, Daryl (Department: 2632)
Communications: electrical
Selective
Interrogation response
C340S010340, C340S010400
Reexamination Certificate
active
06462647
ABSTRACT:
The present invention concerns the field of active transponders and, more precisely, active transponders able to be switched into passive transponders.
There conventionally exist a large number.of portable devices for the contactless identification of an unknown object. A portable device of this type contains data able to be transferred, in the form of radioelectric signals, between a fixed base station acting as transceiver and this device. A portable device of this type is usually made using a transponder.
One will recall that there conventionally exist two types of transponders: passive transponders and active transponders.
A passive transponder is arranged for converting a radioelectric signal originating from a base station, into an electric voltage which then supplies the electric power necessary for the transponder's operation.
A passive transponder of this type includes an antenna to be able to receive and transmit radioelectric signals containing data, a storage capacitor connected to the antenna, to be able to store the electric power received by the antenna, and an integrated circuit connected to the antenna and to the storage capacitor, to be able to process the data received by the antenna, and to provide thereto other data to be transmitted in the form of radioelectric signals. It will be noted that, in such a transponder, the storage capacitor supplies electric power to the integrated circuit.
One drawback of such a passive transponder is that contactless interrogation of the transponder requires a small distance between the base station base and the transponder, this distance being of the order of several meters. It is necessary for the passive transponder to be at a small distance from the base station for the transponder to receive sufficient power for its operation. In the event that such a passive transponder is incorporated in a vehicle door key, the user of the key must therefore be a short distance from the vehicle.
An active transponder is arranged for transmitting data over long distances of the order of several hundreds of meters. Indeed, contactless interrogating such an active transponder does not require a short distance between the base station and the transponder, since no transfer of energy occurs from the base station to the transponder.
FIG. 1
shows an active transponder of this type designated by the reference
1
. This transponder includes an antenna
3
arranged so as to be able to receive and transmit radioelectric signals
4
containing data, an integrated circuit
5
connected to antenna
3
, to be able to process data received by antenna
3
, and to provide the latter with other data to be transmitted in the form of radioelectric signals. Active transponder
1
further includes a battery
7
able to supply power to the various components of transponder
1
.
One drawback of active transponder
1
is that it operates normally, as long as battery
7
provides sufficient electric voltage to supply the set of components of transponder
1
. In the event that the latter is incorporated in a vehicle door key, as soon as battery
7
no longer supplies a sufficient voltage level to assure the proper operation of transponder
1
, the latter no longer allows the door opening command to be provided, which is generally inconvenient for the user of the vehicle.
There also exists in the state of the art <<mixed>> or <<dual>> active transponders, i.e. active transponders which can be switched into passive transponders. GB Pat. No. 2,292,866 discloses such a dual transponder.
FIG. 2
of the present description shows a dual transponder
10
which includes an antenna circuit
11
, a modulation-demodulation circuit
14
, a rectifier circuit
15
, a storage capacitor
16
, a battery
18
, a central processing unit
20
, a read only (ROM) memory
21
, a random-access (RAM) memory
22
, a clock system
23
and a switching circuit
26
.
Antenna circuit
11
is arranged for receiving and transmitting data to and from an external device in the form of a radiofrequency wave
12
. For this purpose, antenna circuit
11
includes an antenna
11
a
formed by a coil and a capacitor
11
b
.
Modulation-demodulation circuit
14
is arranged for modulating a digital signal received from a control circuit
25
into an analogue signal, and for demodulating an analogue signal received via antenna
11
a
into a digital signal. The reference
13
designates a line via which a received signal is transferred from antenna
11
a
to demodulation-modulation circuit
14
, and via which a signal to be transmitted is transferred from modulation-demodulation circuit
3
to antenna
11
a
. Rectifier circuit
15
is formed by a bridge circuit comprising diodes
15
a
to
15
d
for converting an alternating voltage from radiofrequency wave
12
received by antenna
11
a
into a DC voltage V
2
. Storage capacitor
16
is arranged for storing rectified DC voltage V
2
, this latter being intended to be provided to the different components via a connection line
17
.
Central processing unit
20
is arranged for processing data in accordance with an execution programme. ROM memory
21
is arranged for storing the execution programme. RAM memory
22
is arranged for temporarily storing data. Clock system
23
is arranged for providing a clock signal in response to which processing unit
20
operates. The reference
24
designates a bus via which data and addresses are transmitted.
Battery
18
is arranged for providing an electric voltage V
1
intended to supply the various components of transponder
10
, via a connection line
19
. It will be noted that the operating voltage of transponder
10
is of the order of 5 volts.
Switching circuit
26
is connected to lines
19
and
17
, and is arranged so that, when voltage V
2
across the terminals of storage capacitor
16
is greater than voltage V
1
, transponder
10
operates by using the electric power supplied by storage capacitor
16
, via line
17
, and so that, when voltage V
2
is less than voltage V
1
, transponder
10
operates by using the electric power supplied by battery
1
, via line
19
.
One drawback of transponder
10
lies in the fact that, once battery
18
has run down, the electric power supply of the components of transponder
10
can only be supplied by storage capacitor
16
. In the event that transponder
10
is incorporated in a vehicle door key, the transponder must be situated at a short distance from the base station so as to receive sufficient power from the base station to operate. In other words, once battery
18
has run down, the user of the key has to wait the time necessary for capacitor
16
to charge, before identification can occur, which can be particularly inconvenient for the user.
An object of the present invention is to provide a dual transponder which overcomes the drawbacks of conventional active transponders, in particular an active transponder which allows a power supply level sufficient to assure its operation to be maintained.
Another object of the present invention is to provide an active transponder which answers the conventional criteria in the semiconductor industry as to complexity and cost.
These objects, in addition to others, are achieved by the active transponder according to claim 1.
The invention concerns an active transponder including in particular first and second means for comparing respectively the first and second supply signals to a minimum threshold provided by first supply means and, in response, to supply respectively first and second control signals and charging means controlled by the first and second control signals, and arranged so that, when the first and second supply signals are respectively less than and greater than the minimum threshold, the accumulator is charged, via the charging means, from the energy contained in the storage means.
One advantage of such an arrangement of the charging means and the first and second comparison means is that the accumulator charge is controlled, as soon as the supply voltage becomes less than the minimu
EM Microelectronic-Marin SA
Griffin & Szipl, P.C.
Pope Daryl
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