Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1999-02-26
2000-04-18
Hofsass, Jeffery A.
Communications: electrical
Condition responsive indicating system
Specific condition
3405724, G08B 1314
Patent
active
060520558
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
Generally, the invention relates to the remote exchange of information between a portable electrical object, in particular an electronic memory card or chip card, and a terminal by modulation of the magnetic field generated by the terminal.
In this kind of remote data exchange, the magnetic field generated by the terminal serves to energize the electronic components of the portable object, and simultaneously to transmit digital data by modulation.
Various kinds of modulation can be envisaged.
2. Description of the Related Art
At present, use is generally made of frequency or phase modulation for transmitting information between the terminal and the object. In the direction of transmission from the portable object to the terminal, use is generally made of absorption modulation.
For transmission from the terminal to the portable object, it is also possible to envisage another type of modulation, namely amplitude modulation, this offering the advantage of avoiding the use of phase-locked loops and therefore leading to a simple system.
However, given that the portable object, energized by the magnetic field, is subjected to displacements within the magnetic field, especially when the user moves his card towards the terminal and then away from it, the voltage recovered at card level increases when the card is very close to the radiating antenna of the terminal, and may easily reach the breakdown voltage of the junctions of the transistors, thus leading to an impairment of the operation of the electronic components of this card. It is therefore necessary to limit this recovered voltage to a limit value. However, straightforward clipping of the voltage would cause the amplitude modulation of the latter to disappear, which modulation supports the information exchanges.
SUMMARY OF THE INVENTION
The objective of the invention is therefore to afford a solution to this problem and, in particular, to limit the variation in recovered voltage whilst also preserving the digital information contained in this recovered voltage, and to do so in both directions of transmission.
In an embodiment a process for the remote exchange of information between a portable electronic object, in particular a memory card, and a terminal is preferably accomplished by modulation of the magnetic field generated by the terminal. When transmitting information from the terminal to the object, an amplitude modulation of the magnetic field is performed, and when the energizing voltage thus modulated and recovered at an input port of the portable object exceeds a chosen limit value during a modulation peak, this voltage is clipped to said chosen limit value whilst also causing a current to flow through a main transistor connected between said input port arid earth, then, during a modulation trough, a current having a value substantially equal to that of the current flowing during the modulation peak is caused to flow through this main transistor.
Thus, since a substantially constant current is maintained in the transistor between a modulation peak and trough, and since the magnetic field energy or power delivered by the terminal varies between a modulation peak and trough, a decrease will be observed in the voltage energizing the portable object during a modulation trough. Stated otherwise, although the energizing voltage is clipped during a modulation peak, the decrease in its value during a modulation trough will make it easy to detect the variation in the amplitude of the voltage and hence will make it possible not to lose the information transmitted.
The current in the transistor is advantageously kept substantially constant between a modulation peak and trough by keeping he gate voltage of the transistor substantially constant.
For transmitting information from the object to the terminal, which is performed by absorption modulation, an auxiliary transistor mounted in current-mirror mode with the main transistor is switched on or off depending on the logic value of the information bits t
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patent: 5559507 (1996-09-01), Beigel
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patent: 5767789 (1998-06-01), Afzali-Ardakani et al.
patent: 5838235 (1998-11-01), Thorigne
patent: 5883582 (1999-03-01), Bowers et al.
patent: 5923251 (1999-07-01), Raimbault et al.
France Telecom
Hofsass Jeffery A.
Pham Toan
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