Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1998-10-14
2002-11-12
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Interrogation response
C340S010340, C340S572500
Reexamination Certificate
active
06480099
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention concerns a modulation method and a configuration for data transmission from a transponder to a read-write device, where the transponder is supplied with energy from the read-write device via an alternating field and where data transmission is effected in bidirectional mode by modulation of the energy transferring alternating field. A transponder system comprising a read-write device and at least one transponder is described in printed publication DE 42 42 112 A1, for example.
For the transfer of energy from the read-write device to a transponder, an antenna oscillation circuit in the read-write device is supplied with a highfrequency alternating voltage. This produces an electromagnetic alternating field in the coil of the antenna oscillation circuit, which propagates into the space around the read-write device.
This energy transferring, electromagnetic alternating field induces an alternating voltage in one of the transponder antenna circuits, which is described in the following as antenna voltage. The layout of the transponder antenna circuit, comprising primarily a transponder coil and a capacitor connected in parallel, is such that it operates in resonance with the frequency of the antenna oscillating circuit.
The antenna voltage is rectified by a rectifier stage and is available to the transponder circuits, usually a data storage device and a control unit, as a supply voltage. A transponder system represents a loosely coupled transformer, which, because of the low coupling factor, can only transfer very little energy. The coupling factor, and thus the supply voltage available in the transponder, is dependent on the distance from the coil of the antenna oscillating circuit in the read-write device to the coil of the transponder's antenna circuit.
In the case of short distances relative to the read-write device, a transponder can receive so much energy that there has to be a protective circuit to protect the transponder circuits from excessively high supply voltages. A protective circuit of this type—for example—can be implemented by a Zener diode connected against the reference potential.
Data transmission from the read-write device to the transponder is effected by means of a momentary data-sensitive shutdown of the energy transferring alternating field, resulting in data-sensitive field gaps within the energy transferring alternating field; these cause data-sensitive fluctuations of the antenna voltage and of the supply voltage in the transponder. An additional capacitor, arranged in parallel to the transponder circuits, ensures that, during the field gaps in the energy transferring alternating field, the supply voltage does not fall below the minimum operating voltage required by the transponder circuits. The additional capacitor also smoothes the supply voltage for the transponder circuits.
Data transmission from the transponder to the read-write device is effected by data-sensitive modulation of the energy transferring alternating field. To this end, the antenna voltage or the supply voltage of the transponder is attenuated by a modulator, which increases the current flowing in the transponder by the additional connection of a load. The modulator comprises a connected load, arranged in parallel to the transponder antenna circuit. For example, the load may be implemented as a controllable switch, connected against the reference potential.
When the modulator switch is open, i.e. in its unattenuated state, the antenna voltage will only be loaded by the currents of the transponder circuits, the protective circuit and the additional capacitor.
When the switch is closed, i.e. in its attenuated state, an additional current flows through the modulator, which puts a heavy load on the antenna circuit and causes a clear drop in antenna voltage. The difference between the antenna voltage in its attenuated and unattenuated state is designated as an amplitude of modulation voltage. As long as a transponder achieves its typical value for the amplitude of modulation voltage, data transmission is possible from the transponder to the read-write device.
However, the modulator may load the antenna circuit only to the extent that the supply voltage does not fall below the minimum operating voltage value required for the transponder circuits. The drop in antenna voltage is therefore limited to a minimum value. This means that the amplitude of modulation voltage which the modulator produces is dependent on the difference between the antenna voltage and the minimum operating voltage required for the transponder circuits.
The main disadvantage of a transponder set up in this way is that, if the distances from the transponder to the read-write device are such that the supply voltage is only just sufficient to operate the transponder circuits, the amplitude of modulation voltage which can be achieved by the modulator will no longer be sufficient for data transmission from the transponder to the read-write device.
SUMMARY OF THE INVENTION
The invention is based on the task to specify a modulation method for data transmission from a transponder to a read-write device which avoids this disadvantage.
According to the invention, this task is solved by a modulation method for transmitting data from a transponder to a read-write device, wherein the transponder is provided with a modulator for generating a modulation voltage amplitude, and wherein the modulation voltage amplitude is caused by a reduction in the transponder supply current flowing in the transponder. With the modulation method for data transmission from a transponder to a read-write device in accordance with this invention, the amplitude of modulation voltage produced by a modulator will be effected by a reduction in the supply current flowing within the transponder.
The modulator will be formed by a circuit to produce a voltage drop and to reduce the supply current flowing in the transponder. For example, this circuit can be formed by a modulator resistor, which can be bridged by a controllable switch connected in parallel.
The amplitude of modulation voltage in the transponder is effected by bridging the modulator resistor. No additional load is connected in the transponder, instead the load for the antenna circuit is reduced. This reduces the supply current flowing in the transponder, and consequently the load in the antenna circuit is reduced, and the antenna voltage increases.
In this way the energy which, during data transmission from the transponder to the read-write device, must be withdrawn from the antenna circuit in order to attenuate the energy transferring alternating field is not consumed in the additional load; instead the energy is stored in an additional capacitor and can be made available to the transponder circuits as and when required.
The transponder comprises an antenna circuit containing a transponder coil with a capacitor connected in parallel, a rectifier, a modulator, a clamping and protective circuit, an additional capacitor and the transponder circuits. Here, the modulator is arranged in series between the antenna circuit and the transponder circuits. The rectifier is arranged in series before or after the modulator. The clamping and protective circuit and the additional capacitor are arranged in parallel to one another between the modulator and the transponder circuits.
The transponder circuits comprise a demodulator, a data storage device and a control unit, arranged in parallel to one another.
With distances between the transponder and the read-write device where the transponder circuits are only just supplied with sufficient energy, this has the effect of ensuring data transmission from the transponder to the read-write device. There is an increase in the distance at which data transmission can still occur.
The modulation method according to the invention is particularly suitable for transponders with transponder circuits where the power consumption is not negligible and cannot be disregarded.
The minimum setup for transponder circuits is a demodulator, a da
Kunitz Norman N.
TEMIC Semiconductor GmbH
Venable
Zimmerman Brian
LandOfFree
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