Telecommunications – Transmitter and receiver at separate stations – Near field
Reexamination Certificate
2000-11-21
2004-09-28
Craver, Charles (Department: 2682)
Telecommunications
Transmitter and receiver at separate stations
Near field
C455S558000, C340S315000
Reexamination Certificate
active
06799015
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electromagnetic transponder, that is, a transceiver (generally mobile) likely to be interrogated contactless and wireless by a unit (generally fixed), called a read and/or write terminal. The present invention more specifically relates to transponders having no independent power supply. Such transponders extract the power supply required by the electronic circuits included therein from the high frequency field radiated by an antenna of the read/write terminal. The present invention applies to such transponders, be they read-only transponders, that is, transponders adapted to operating with a terminal which only reads the transponder data, or read/write transponders, which contain data that can be modified by the terminal.
BACKGROUND OF THE INVENTION
Systems using electromagnetic transponders are based on the use of oscillating circuits, including a winding forming an antenna, on the transponder side and on the read/write terminal side. These circuits are intended to be coupled by a magnetic field when the transponder enters the field of the read/write unit.
FIG. 1
very schematically shows a conventional example of a data exchange system between a read/write unit
1
and a transponder
10
of the type to which the present invention applies.
Generally, terminal
1
is essentially an oscillating circuit formed of an inductance L
1
in series with a capacitor C
1
and a resistor R
1
, between an output terminal
2
of an amplifier or antenna coupler (not shown) and a reference terminal
3
. The antenna coupler belongs to a circuit
4
for controlling the oscillating circuit and exploiting received data including, among others, a modulator-demodulator and a microprocessor for processing the control signals and the data. In the example shown in
FIG. 1
, node
5
of the connection of capacitor C
1
to inductance L
1
forms a terminal for sampling a data signal received from the demodulator. Circuit
4
of the terminal generally communicates with different input/output circuits (keyboard, screen, means of transmission to a provider, etc.) and/or processing circuits, not shown. The circuits of the read/write terminal draw the power required by their operation from a supply circuit (not shown) connected, for example, to the electric supply system.
A transponder
10
, intended for cooperating with a terminal
1
, essentially includes a parallel oscillating circuit formed of an inductance L
2
, in parallel with a capacitor C
2
between two input terminals
11
,
12
of a control and processing circuit
13
. Terminals
11
,
12
are in practice connected to the input of rectifying means (not shown), the outputs of which form D.C. supply terminals of the circuits internal to the transponder. Since transponder
10
draws its power from the field radiated by terminal
1
, it is necessary to provide means
14
for limiting the input voltage of circuit
13
that would otherwise risk being damaged by too high voltages. Means
14
are symbolized in
FIG. 1
by a zener diode forming means for clipping the voltage across capacitor C
2
. Means
14
are shown to be in parallel with capacitor C
2
. It should however be noted that any other equivalent means may be used and that the clipping means may be placed downstream of the rectifying means.
The oscillating circuit of terminal
1
is excited by a high-frequency signal (for example, 13.56 MHz) intended to be sensed by a transponder
10
. When transponder
10
is in the magnetic field of terminal
1
, a high-frequency voltage is generated across terminals
11
,
12
of the transponder's resonant circuit. This voltage, after being rectified, is intended to provide the supply voltage for the electronic circuits
13
of the transponder. These circuits generally essentially include a microprocessor, a memory, a demodulator of the signals possibly received from terminal
1
, and a modulator for transmitting information to the terminal.
The oscillating circuits of the terminal and of the transponder are generally tuned on the frequency of a transmission carrier, that is, their resonance frequency is set to a frequency of, for example, 13.56 MHz. This tuning aims at maximizing the power diffusion to the transponder, generally, a card of credit card format or a tag of still smaller format, integrating the different transponder components.
The high-frequency remote supply carrier transmitted by the terminal is also used as a data transmission carrier. This carrier is generally modulated in amplitude by the terminal according to different coding techniques to transmit the data to the transponder.
FIG. 2
illustrates a conventional example of a data transmission from terminal
1
to a transponder
10
. This drawing shows an example of a shape of the excitation signal of antenna L
1
for a transmission of a code 0101. The modulation currently used is an amplitude modulation with a 106-kbit/s rate (1 bit is transmitted in approximately 9.4 &mgr;s) much smaller than the frequency (for example, 13.56 MHz) of the carrier coming from the transmission oscillator (period of approximately 74 ns). The amplitude modulation is generally performed with a modulation rate (defined as being the difference of the peak amplitudes (a, b) between two states (1 and 0) divided by the sum of these amplitudes) much smaller than one due to the need for supply of transponder
10
. In the example of
FIG. 2
, the 13.56-MHz carrier is modulated in amplitude, with a 106-kbit/s rate, with a modulation rate tm of, for example, 10%. It should be noted that, whatever the type of modulation used (for example, amplitude, phase, or frequency modulation) and whatever the type of data coding (NRZ, NRZI, BPSK, Manchester, ASK, etc.), the transmission is performed by jumps between two binary levels on the remote supply carrier.
A disadvantage of conventional transponders is that the use of means for clipping the voltage recovered across the oscillating circuit (L
2
, C
2
,
FIG. 1
) is incompatible with an amplitude shift keying that is not in all or nothing. Indeed, if the transponder is relatively close to the terminal, the voltage is likely to be clipped in such a way that the transponder demodulator is then incapable of making out a state 0 from a state 1 due to the modulation rate used. Further, this loss of information can occur without having a clipping level lower than the level of state 0 (b, FIG.
2
). It is indeed sufficient for the level at state 1 to be clipped to have a risk of interpretation error by the transponder demodulator.
A known solution to solve this problem consists of limiting the transmission power of the terminal so that a transponder located very close to the terminal does not receive a voltage such that its clipping means are active. A disadvantage of such a solution however is that this then limits the range of the transponder system.
Further, the magnetic fields that the transponders are supposed to withstand are most often imposed by industry or government standards and the application of the standards now in force results in a magnetic field received by the transponder, when its clipping means operate, which is much smaller than the maximum magnetic field that the transponder must be able to withstand according to the standards.
The above problems are more critical still for low power consumption transponders that are tuned on the resonance frequency. Indeed, in such a case, the circuits internal to the transponder provided to have a low consumption are not able to withstand high voltages, so that the clipping means must be sized accordingly.
SUMMARY OF THE INVENTION
The embodiments of the present invention overcome the disadvantages of known electromagnetic transponders as concerns the unwanted effects of the clipping means.
The embodiments of the present invention more specifically aim at providing a novel electromagnetic transponder that can withstand high magnetic fields in the vicinity of a read/write terminal without adversely affecting the recovery of the data transmitted by this terminal. This requir
Craver Charles
Jorgenson Lisa K.
Seed IP Law Group PLLC
STMicroelectronics S.A.
Tarleton E. Russell
LandOfFree
Electromagnetic transponder with a frequency detuning does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electromagnetic transponder with a frequency detuning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electromagnetic transponder with a frequency detuning will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3268670