EP0898762A1

EP0898762A1 - Data exchanging system with communication with or without contact between a terminal and portable objects

Info

Publication number: EP0898762A1
Application number: EP97951297A
Authority: EP
Inventors: Frédéric WEHOWSKI
Original assignee: Innovatron Industries SA
Current assignee: Regie Autonome des Transports Parisiens
Priority date: 1996-12-10
Filing date: 1997-12-10
Publication date: 1999-03-03
Also published as: JP4199300B2; HK1018830A1; KR19990082449A; TR199801538T1; EP0901670B1; TR199801539T1; DE69729865T2; PT901670E; DE69729865D1; BR9707629A; CN1214135A; ATE271242T1; FR2756953A1; BR9707628A; DK0901670T3; US6636146B1; KR19990082448A; EA199800707A1; MXPA98006460A; WO1998026371A1

Abstract

The portable object (200) comprises a plurality of electric contacts for communicating by galvanic channel with a terminal of a first type itself comprising a plurality of homologous electric contacts, and a coil (102) for communicating without contact with a terminal of a second type (100) transmitting in modulated electromagnetic field transmitting data. The data transmitted by the terminal are timed by a clock signal, and the portable object comprises means for clock detecting (220) to modify the functioning of the portable object depending on the presence or the absence of a clock signal (CLK) in the received signal, in particular the signal picked up by the coil. These means can in particular monitor protocols of communication and/or of signal processing and/or of received data processing, and means for interrupting the connection between the electric contacts and other circuits of the portable object.

Description

Data exchange system with contact or contactless communication between a terminal and portable objects

The invention relates to contactless communication techniques between a portable object and a terminal.

Contactless data exchange is well known; among the applications of this technique, there is - but not limited - the ^access control, electronic payments (such applications, "electronic purse") and electronic toll collection, for example to ^access and toll transport in common.

In the latter example, each user is provided with a portable object of the "contactless card" or "contactless badge" type, which is an object capable of exchanging information with a fixed (or possibly mobile) "terminal". approaching the badge of the latter so as to allow a non-galvanic mutual coupling ("terminal" will be the term used in the present description to designate the data transmitter / receiver terminal able to cooperate with portable objects).

More precisely, this coupling is carried out by varying a magnetic field produced by an induction coil (technique naked under the name of "induction process"). To this end, the terminal includes an inductive circuit excited by an alternating signal which produces an alternating magnetic field in the surrounding space. The portable object in this space detects this field and return modulates the load of ^the portable object coupled to the terminal; this variation is detected by the terminal, thus establishing the bidirectional communication sought.

Furthermore, there is a large fleet of electrical contact terminals which communicate galvanically with existing portable objects, in particular those commonly designated "smart cards". For this reason, among other things, it is advantageous to have portable objects capable of communicating with terminals either by galvanic way (by contacts) or by non-galvanic way (without contact). EP-A-0 424 726 describes such a mixed card capable of communication with or without contact. In this card, communication is established selectively via contact pads or via coils, depending on the presence of an electrical voltage on the pads or on the coils.

A disadvantage of this system, however, is that piloting as a function of the presence of a voltage proves difficult to apply in practice. In particular, the appearance of parasites can disturb its operation. Thus, a parasitic depletion of the supply voltage to the contacts may cause the accidental selection of the communication channel by coil and ^activation of a shunt regulator, wherein while circulating an excessive current when it is put in parallel with the power contacts. This system is also unsuitable for selecting the starting and operating conditions of the processing circuit, the disappearance of the contact power supply causing a parasitic starting. Selection at start-up based on information from the comparison of the two power sources presents the difficulty of locking the selection at the right time under all power-up conditions.

One of the aims of the present invention is to propose another way of detecting the communication mode to be used and to control various functions of the portable object accordingly. The portable object of the ^invention is of the general type disclosed by EP-A-0,424,726 cited above, namely having a plurality of electrical contacts for communication galvanically with a terminal of a first type having itself a plurality of homologous electrical contacts, as well as a coil for contactless communication with a terminal of a second type emitting a modulated electromagnetic field transmitting data.

It is characterized in that, the data transmitted by the terminal being clocked by a clock signal, it comprises clock detector means for modifying the operation of the portable object as a function of the presence or of the absence of a ^clock signal in the received signal.

Preferably, these means clock detectors detect the ^clock signal in the signal picked up by the coil. Also preferably, in contactless communication mode, the portable object is remotely powered by the electromagnetic field received by the coil and the clock signal, and then includes rectifying and filtering means to obtain a DC supply voltage. for the object in contactless communication mode from the electromagnetic field picked up by the coil, and the detector means receive as input the signal present between the coil and the rectification and filtering means (where its amplitude is the greatest) .

The clock signal can be extracted at the same place. In particular, the clock can be defined by the frequency of the carrier received, divided into the means for extracting the clock.

This allows a more sensitive but also more reliable detection of the presence of the clock signal. The data itself is preferably extracted downstream from the rectification and filtering stage, so that the demodulation of the signal is more stable, in particular in the case of amplitude modulation.

According to various advantageous subsidiary characteristics, provision is made:

Means for demodulating the signal picked up by the coil, so as to extract communication data therefrom, in particular amplitude demodulating means operating on the signal delivered in exit from the rectification and filtering stages;

- downstream of the rectification and filtering means, regulating means to stabilize the DC voltage, as well as means of selective inhibition of the regulating means, controlled by the clock detector means;

Means for transmitting data from the portable object to the terminal in contactless mode by modulating the load at the terminals of the coil; advantageously, the modulation is then a modulation of a subcarrier produced by division of the fre- quency of ^the clock supplied by the detection means and / or the circuit is capable of two modes of operation in nominal consumption and low consumption , and means are provided for placing the circuit in low consumption mode before the data transmission means begin to operate said modulation;

The clock detector means can control communication and / or signal processing and / or data processing protocols received. Thus, the signal presence / absence clock can be operated in several ways, for example by providing the signal in- HIBITION ^a regulator that stabilizes the DC voltage supply so that the controller operates that in contactless mode. The risk of inadvertent activation of this shunt regulator is eliminated. Also, this signal can be used in the development of the activation signal of the processing circuit and the selection of its clock signal. Finally, the communication and signal processing protocols can differ between the contact and contactless communication modes and the presence / absence of ^a clock can be used to control the protocols used.

Finally, it may be desirable to provide means switches the connection between the electrical contacts and ^other circuits of the portable object, controlled by the detector means so as to interrupt said connection when the portable object clock communicates contactless track. This makes it possible to avoid fraud attempts by capturing and deciphering the signals which would otherwise appear on the contacts, which are accessible in this communication mode. Usefully, an analog switch can be also provided for interrupting the li-, aison communications mode by contacts, thus allowing to avoid interpreting as parasites of the data appearing on ^the input (coil or contacts) unused. In an advantageous embodiment of a portable object remotely supplied in contactless mode, there is provided downstream of the rectification and filtering stages a stabilizing stage comprising a shunt regulator element mounted in shunt between the supply terminals of the circuit to be supplied and associated with a resistive component connected in series in the circuit supply line, the shunt regulating element taking and deriving a variable fraction of the circuit supply current so that the resistive element and the shunt regulating element dissipate any additional energy not necessary for the operation of the circuit, so as to correlate, stabilize the supply voltage at the terminals of the circuit, limit the voltage excursion at the terminals of the element tuned upstream and prevent variations in the current consumed influence upstream on the ^amplitude of the signal to be demodulated.

In particular, means may be provided to inhibit selective tively and temporarily the operation of the shunt regulator, in particular in response to the detection ^of a type of communication via contacts.

Finally, the entire electronic circuit of the portable object, with the exception of the winding of the tuned element, is very advantageously produced in integrated monolithic technology.

0

An embodiment of the invention will now be described in detail, with reference to the accompanying drawings in which the same reference numerals designate identical or functionally similar elements.

Figure 1 is a block diagram ^of a system according to the invention, in its most general aspect, comprising a terminal and a tative Por- object in the field of this terminal. FIG. 2 shows a particular embodiment of the portable object of FIG. 1.

Figure 3 details the regulator circuit of the diagram in Figure 2.

Figures 4 and 5 detail, in two possible variants, the demodulator circuit of the diagram of Figure 2.

FIG. 6 is a detailed example of an embodiment of the demodulator circuit of FIG. 5.

Figure 7 details the clock extractor circuit of the diagram in Figure 2. Figure 8 is a series of timing diagrams explaining how the portable object is remotely powered and from which the clock signal is extracted.

Figure 9 is a series of timing diagrams explaining the transmission of information from the terminal to the object. Figure 10 is a series of waveform diagrams explaining the transmission ^of information from the object to the terminal.

FIG. 11 shows the different switches operated in a mixed card between the two contact / contactless modes of operation. 0

An example of implementation of the system of the invention will be explained with reference to the diagram in FIG. 1. In this diagram, the reference 100 designates a terminal, which can be coupled with a portable object 200 placed in its vicinity .

The terminal includes a transmission coil 102 which, associated with a capacitor such as 104, forms a tuned circuit 106 intended to generate a modulated magnetic induction field. The tuning frequency of circuit 106 is for example 13.56 MHz, a value of course in no way limiting, this particular choice simply due to the fact that it corresponds to a value authorized by European standards for communication and remote power supply functions . In addition, this relatively high value makes it possible to design circuits with coils having few turns, therefore easy and inexpensive to produce. The tuned circuit 106 is supplied from a high-frequency continuous wave oscillator 108 and, for modulation, from a mixer stage 108 controlled by the signals to be transmitted TXD from a digital circuit 112. The operation of circuit 112 , and in particular the sequencing of signals TXD, is clocked by a circuit 114 producing a clock signal CLK.

The reception stages, which extract the data received RXD from the signal taken from the terminals of the coil 102, comprise a high-frequency demodulator circuit 116 as well as a sub-carrier demodulator circuit 118 when one has chosen, as is will indicate below, to use a subcarrier modulation in the portable object → terminal direction (this technique is of course in no way limiting, the modulation can also be done in baseband).

The portable object 200, meanwhile, includes a coil 202 co-operating with an electronic circuit 204 which advantageously is made of fully integrated monolithic technology so as to have ^an object of small dimensions, typically in the format "map credit ^' '; the coil 202 is for example a printed coil and all of the circuits 204 are produced in the form of a specific integrated circuit (ASIC).

The coil 202 forms with a capacitor 206 a resonant circuit 208 tuned to a given frequency (for example 13.56 MHz) allowing the bidirectional exchange of data with the terminal by the technique called "by induction" as well as the remote supply by the field magnetic picked up by the coil 202, that is to say the same coil as that used for the exchange of information.

The alternating voltage collected at the terminals of the tuned circuit 208 is applied to a single or full alternating rectifier stage 210, then to a filtering stage 212, to give a filtered rectified voltage b.

The portable object also includes a digital processing stage 214, typically made from ^a microprocessor, memories RAM, ROM and EPROM and interface circuits.

Downstream of the rectification 210 and filtering 212 stages are mounted in parallel a number of specific stages, including nant:

A regulator stage 216, voltage stabilizer, delivering a direct, rectified, filtered and stabilized voltage d, applied in particular to the positive supply terminal VCC of the digital circuit 214, the other supply terminal of which is GND mass.

This stabilizer stage 216 can be a conventional type voltage stabilizer or, as a variant (but not limited to), a specific circuit which will be described below with reference to FIGS. 2 and 3. - a demodulator stage 218 receiving as input signal b and outputting a demodulated signal e applied to the RXD data input of digital circuit 214.

This demodulator can in particular be a demodulator with amplitude variation detection and / or with variable threshold, as will be explained in more detail below with reference to FIGS. 4, 5 and 6.

- an extractor stage ^clock 220. receiving as input the signal collected at the terminals of the tuned circuit 208 and outputting a ç applied to the clock input CLK of the digital circuit signal 214. ^The clock extractor stage of 220 can be placed either upstream of the rectification 210 and filtering stages 212, as illustrated, or downstream of these stages, that is to say operate on the signal b instead of the signal a; this latter variant is less advantageous, however, insofar as the clock extractor will then have to have greater sensitivity to compensate for the smoothing of the input signal by filtering.

A modulator stage 222 which operates, in itself known, by "charge modulation", a technique consisting in varying in a controlled manner the current consumed by the tuned circuit 208 situated in the surrounding magnetic field generated by the terminal.

This modulator circuit 222 comprises a resistive element 224 (added resistance or, in monolithic technology, MOS type component without grid acting as a resistance) in series with a switching element 226 (MOS transistor) controlled by the modulation signal f present on the TXD output of digital circuit 214. As a variant, the modulator stage 222, instead of being placed downstream of the rectification 210 and filtering 212 circuits, can also be placed upstream of these circuits, as illustrated at 222 ′ in FIG. 1, it is ie directly across the resonant circuit 208.

The general structure and proposed, wherein the demodulator stage 218 is located downstream of the recovery stages 210 and filter 212, has ^the advantage of being less sensitive to instantaneous variations in the signal. Indeed, in ^the case of a remotely powered portable object, the fact of operating the demodulation on a rectified and filtered signal to reduce the effects of the instantaneous power of the energy changes in ^a cycle of oscillation.

This aspect will be better understood when the detailed operation of the demodulator is exposed, with particular reference to the timing diagrams of FIG. 8.

Will now be described with reference to Figure 2, a particular embodiment of the structure of Figure 1, which is in particular characterized by a particular structure given to the floor controller 216 which, as ^will be explained in more detail later, a floor type "shunt ^regulator" with a shunt component 228 for deriving a controlled manner the supply current of the digital circuit 214, therefore mounted in parallel between the terminals VCC and GND, combined with a 230 series resistive element placed in the VCC supply line upstream of the regulator component 228.

The shunt 228 can advantageously be a Zener diode or, preferably, a component or integrated functionally equivalent to a Zener diode, for example a component of the LM185 / LM2S5 / LM385 series from National Semiconductor Corporation, which is a component forming reference reference. voltage (fixed or adjustable voltage as appropriate), with a bias current of only 20 μA, a very low dynamic impedance and a range of operating currents from 20 μA to 20 mA. Component 228 can also be a monolithic equivalent, integrated on the ASIC, of such a voltage reference component. Figure 3 depicts one particular embodiment of this circuit 216 with a component of the type described above in which ^the voltage reference input 234 is biased to a predetermined value by a voltage divider 236, 238 connected between VCC and ground. The resistive element 230 can be an added resistance or, advantageously, an integrated monolithic component, for example (as for the component 224) an MOS element acting as a resistance.

It further provides, advantageously, a switching component, such as ^a MOS transistor 240, which is maintained by passing normal func- tioning by applying a signal INH / to its gate. This transistor can be switched to the off state by applying a simple INH control signal (in particular a software command from the computing circuit 214) which has the effect of inhibiting the operation of the shunt regulator, the circuit behaving then as if it had been omitted.

This possibility of inhibiting the shunt regulator can in particular be used when it is desired to supply the microprocessor with a high voltage without risk of destroying the regulator stage.

This occurs especially for the needs of a test, or lors- eu ^one is in the presence of a mixed portable object that can be used to choose in "contactless" (with time the controller service) or Mode ^"with contacts" (with inhibition of the regulator), the regulated supply voltage being in the latter case directly applied to ^one of contacts of the portable object without ^it being necessary to proceed to a specific regulation, as in the case of remote power supply.

The amplitude demodulator stage 218 will now be described in more detail, with reference to FIGS. 4 to 6.

This demodulator ^amplitude is a circuit suitable for processing modulated signals with a low modulation depth. The expression “shallow modulation depth” or “weak modulation” will be understood to mean a modulation whose rate is typically less than or equal to 50%, preferably less than 20%, the “rate” being defined as being the ratio

(A max -A mi • rr) / (A max + A • m) "of maximum levels A_ max and minimum A_ mi.n the amplitude of the considered signal. Indeed, in the particular context ^of a portable object teleali- It is therefore advantageous, given the energy constraints, to use a low modulation rate in order to be able to have sufficient energy during the period when the modulation is in the low state, since, due to the modulation in amplitude, the instantaneous energy level supplied to the portable object varies directly with the level of the modulation.

FIG. 4 illustrates a first possible variant embodiment, where the demodulator is an adaptive variable threshold demodulator. The circuit comprises, after an optional low-pass filtering stage 242, a comparator 244, preferably with hysteresis, whose positive input receives the signal b to be demodulated (if necessary filtered by stage 242) and whose negative input receives this same signal b, but after crossing an RC stage 246, 248 acting as an integrator. The comparison is thus made between, on the one hand, the instantaneous value of the signal and, on the other hand, an average value of this signal, constituting the variable comparison threshold.

FIG. 5 illustrates a second possible variant embodiment of the demodulator 218, which in this case is a demodulator sensitive to amplitude variations. After an optional low-pass filtering stage 242, the signal b is applied to a stage CR 250, 252 acting as a differentiator. The output signal is applied to the positive terminal of comparator 244 (here again preferably with hysteresis) whose negative input is connected to a fixed potential, for example ground. In this case, the demodulator is sensitive to variations in the amplitude (due to the differentiating stage), independently of the average value of the signal; it is only the variations of this average value that the comparator detects.

FIG. 6 gives a more detailed example of an embodiment of such a demodulator circuit with detection of amplitude variations. In addition to the low-pass filter 242 consisting of the resistor 252 and the capacitor 254, there is the series capacitor 250 acting as a differentiator in combination with the resistors 256 to 264. The signal thus differentiated is applied to two symmetrical comparators 244, 266 of which the outputs act on two flip-flops 268, 270 mounted in a flip-flop so as to produce two symmetrical signals RXD and RXD / shaped appropriately.

FIG. 7 illustrates an exemplary embodiment of the extractor and clock detector circuit 220.

This circuit receives as input a signal taken from the terminals of the resonant circuit 208 and applied to the differential inputs of a hysteresis comparator 272 which supplies the clock signal CLK. The clock signal is also applied to two inputs of an EXCLUSIVE OR gate 274 directly on one of ^the inputs, and through an RC circuit 276, 278 on the other input. This RC circuit, which introduces a delay in the transmission of the received signal, is chosen with a time constant of the order of l / 4f _CLK (c K e ing the clock frequency generated by the circuit 114 of the terminal 100). The output signal from gate 274 is then averaged by an RC circuit 280, 282 whose time constant is much greater than l / 2.f _CLK (preferably of the order of l / f _{L κ} ) and then applied to one of the inputs of a comparator 284 for comparison with a fixed threshold S.

The clock signal CLK allows the appropriate timing of the digital processing circuit 214, while the output of the comparator 284 gives a signal PRSCLK indicative of the presence or not of a clock signal.

In the case of a mixed board adapted to operate indifferently in "contactless" mode, or in "contact", the PRSCLK signal presence / absence of ^the clock signal is advantageously used to signal to the digital circuit that the object is in a "contactless" type environment and decide on corresponding actions such as selection of the appropriate communication protocol, activation of the shunt regulator, PRSCLK being used to produce INH / (see description above with reference to figure 3), etc.

FIG. 11 presents in detail the various switches which are thus automatically operated between the "contactless" and "contactless" modes. Contacts 286 are the CLK (clock), GND (ground), I / O (data), VCC (power) and RST / (reset) contacts of ISO 7816-3, which will be referred to for more details. The various switches 288 to 296 are all represented in the "contact" position (referenced '0'), default position, their toggle- ment to the "contactless" position (referenced 1 ') being controlled by the signal PRSCLK delivered by the circuit 220, revealing the presence of a clock signal coming from the rectifying and filtering means. The ^extraction of a clock signal is also particularly advantageous when it is desired to achieve a modulation not in baseband but modulated subcarrier as the subcarrier can easily be generated by dividing the clock frequency. The digital circuit 214 then adds the subcarrier thus generated to the data to be transmitted to produce the signal TXD applied to the charge modulator circuit 222.

In a variant, it is possible to detect the presence of the clock signal on the contact pad CLK, rather than in the signal coming from the coil (therefore from the clock extractor 220). This makes it possible to reverse the operation of the switches 288 to 296 and to add a clock presence detector with the contact pad CLK as input, by supplying the signal PRSCLK in place of the extractor 220.

This variant however has some drawbacks. Thus, if the contacts with mode communication is done in accordance with ISO 7816-3, the clock signal appears only after ^the emergence of tensions in other contact pads, and appropriate measures can be made necessary to prevent the shunt regulator (provided for remote power supply by the coil) from excessively charging VCC at the start of a communication with contacts.

We will now describe the operation of the portable object, with reference to the timing diagrams of FIGS. 8 to 10.

We will first of all explain, with reference to the timing diagrams of FIG. 8, the way in which the object is supplied and in which it recovers the clock signal.

The tuned circuit 208 captures part of the magnetic energy produced by the terminal. The corresponding alternating signal a, illustrated in FIG. 8, is rectified by block 210 and filtered by capacitor 212, to give a filtered rectified voltage b illustrated in FIG. 8. For an alternating signal a with a peak voltage of 10 N , a rectified and filtered voltage is thus obtained having a peak voltage of the order of 8.5 V. Of course, the amplitude of the voltage a, and therefore of the voltage sion b, very much depends on the distance between object and terminal, the amplitude being all the more important as the object is near the terminal. The regulator stage 216 intervenes to compensate for these variations, by delivering to the digital circuit 214 a stable voltage, typically of the order of 3 V (timing diagram d of FIG. 8).

Thus, when one is far enough from the terminal, almost at the range limit, the voltage in b will be fairly close to the required value of 3 V, the voltage drop between b and d will be low, the current passing through the shunt 228 will also be very weak and almost all of the current delivered by the supply circuit will be used to supply the digital circuit 214. It will be noted that, in this case, the current flowing through shunt 228 may be as low as a few microamps only (minimum bias current).

On the other hand, when the object is very close to the terminal, the voltage in b will be high, the potential difference between b and d will also be significant (several volts), and the current passing through the shunt 228 will be high, the element resistive 230 and the shunt 228 dissipating the excess energy.

In addition to the purely electrical role of stabilizing the power supply of digital circuit 214, the shunt regulator stage provides several advantages within the framework of the circuit that has been described.

First, it limits the voltage excursion at b _. , therefore in a, when the object is close to the terminal, due to the low charge which is presented downstream of the tuned circuit 208: due to the large current flowing in the shunt 228, the power collected not essential to the operation of digital circuit 214 is completely dissipated as heat.

This is particularly advantageous when the capacitor 206 of the tuned circuit 208 is an element produced in integrated monolithic technology, since the risks of breakdown due to overvoltages are thus avoided. Indeed, given the geometric constraints of the integrated circuit, it is not possible to produce capacitors having high breakdown voltages. Or the digital circuit 214, which is built around ^a microprocessor, requires for its power supply a relatively large power, so a level field magnetically that high enough, which could create overvoltages in the tuned circuit if the indicated precautions were not taken.

Secondly, as will be explained in more detail below, the shunt regulator has the effect of equalizing instantaneous variations in the supply current of the digital circuit (the consumption of such a circuit is indeed not constant) and to avoid their repercussions on the functioning of the other organs of the circuit, for communication both from the object to the terminal and from the terminal to the object; in fact, undesirable variations in current or voltage could introduce modulation or demodulation errors.

Finally, in the case where the object is at the limit of range of the terminal, and where it therefore receives from the terminal only a signal just sufficient to supply the digital circuit, the design of the circuit makes it possible to avoid any waste of energy, since the current in shunt 228 is practically zero. Thus, all the available energy captured by the tuned circuit can be used to operate the digital circuit.

As regards the clock signal, the clock extractor circuit 220 makes it possible to transform the alternating signal picked up at the terminals of the tuned circuit 208 into a series série of perfectly calibrated clock pulses.

We will now describe the way in which the information is transmitted from the terminal to the object, with reference to the timing diagrams in FIG. 9.

To transmit information to the object, the terminal modulates the amplitude of the magnetic field it produces. The information sent is binary, this modulation amounts to decrease ^by a predetermined amount, for example 10%, ^the signal amplitude. Such a reduction corresponds for example to ^the transmission ^of a logical '0', the maximum amplitude for a remaining the logic: see Figure 9 is the timing diagram of the signal picked up by the tuned circuit 208.

This is translated after rectification and filtering, in b. by a reduction in the amplitude of the rectified and filtered signal. This reduction in amplitude is detected by the amplitude demodulator 218, which outputs the logic signal e applied to the digital circuit. It will be noted that the reduction in amplitude resulting from the modula- tion of the signal sent by the terminal has no effect on the clock extractor (signal ç) and on the supply voltage supplied to the digital circuit (signal d).

If techniques other than amplitude modulation were used in the terminal → object direction, for example phase modulation as taught by numerous documents of the prior art, the type of modulation would have no direct effect on the operation of the regulator circuit of the invention; however, this circuit is particularly advantageous in the case of amplitude modulation since, as explained, it makes it possible to perfectly overcome the various drawbacks associated with the choice of this technique.

How the information is transmitted in turn will be explained, ^the object to the terminal, with reference to timing diagrams of Figure 10. ^As was mentioned above, in the illustrated embodiment is performed by load variation, that is to say controlled variation of the current consumed by the tuned circuit 208. To this end, the resistive element 224 is selectively switched by the component 226, the resistance being for example switched when the object wants to send a logical '0', not switched for a logical '0'.

When the resistor is switched, that is to say for a logic '0', the voltage a decreases due to the additional load. The resistance value is of course chosen so that this voltage drop nevertheless makes it possible to maintain a correct supply of the digital circuit.

One can, however, be faced with a difficulty when one is at the limit of range of the terminal. Indeed, in this case, the current which must be diverted in the resistive element 224 to generate the modulation may be still too high for the digital circuit to be able to continue to function properly.

In this case, provision is advantageously made, before the object begins to send information to the terminal, to place the digital circuit in a "low consumption" mode so as to be able to consume more current in the resistive element 224 without threatening the power supply of the digital circuit. This can for example be achieved by the microprocessor program of the digital circuit which, before starting to send data to the terminal, will place the transmission routine in RAM (whose access consumes little energy) and disconnect the EPROM memory (access to which requires significantly higher energy). In other words, the digital circuit goes into "low consumption" mode to have a large reserve of current, which will be consumed in the modulation resistance for sending messages to the terminal.

Also, ^if you can spend more im- modulation current carrying in the resistive element 224 (by choosing a lower resistance value) modulation will be better for side terminal, which will be content to the terminal, less elaborate detection means EFOU to have ^a better signal to noise ratio.

It is possible, still in the object → bound direction, to use other types of modulations or variants, for example, as indicated above, the modulation of a subcarrier which controls the charge variation at instead of a load modulation directly by the signal to be transmitted.

Claims

1. A portable object (200) comprising a plurality of electrical contacts (286) for communication by galvanic means with a terminal of a first type itself comprising a plurality of homologous electrical contacts, as well as a coil ( 102) for contactless communication with a terminal of a second type (100) emitting a modulated electromagnetic field transmitting data, characterized in that, the data transmitted by the terminal being clocked by a clock signal, it comprises clock detector means (220) for modifying the operation of the portable object as a function of the presence or absence of a clock signal in the received signal.

2. The portable object of claim 1, wherein the means de- clock detectors (220) detects the ^clock signal (CLK) in the signal picked up by the coil.

3. The portable object of claim 2, comprising rectifying and filtering means (210, 212) for obtaining a continuous supply voltage (d) for the object in contactless communication mode from the electromagnetic field picked up by the coil, and in which the detector means receive as input the signal present between the coil and the rectifying and filtering means.

4. The portable object of claim 2, comprising means

(218) for demodulating the signal picked up by the coil, so as to extract communication data therefrom.

5. The portable object of claims 3 and 4 taken in combination, in which the demodulator means are amplitude demodulator means (218) operating on the signal (b) output from the rectification and filtering stages (210, 212).

6. The portable object of ^one of claims 3 to 5, comprising, downstream of the rectifying means and filter means regulators (216) for stabilizing the DC voltage, and means of selectively inhibiting means regulators, controlled by the detection means ^clock.

7. The portable object of one of claims 1 to 6, comprising means (222) for transmitting data from the portable object to the terminal in contactless mode by modulating the load at the terminals of the coil.

8. ^The portable object of claim 7, wherein the modulation performed by the data transmission means is a modulation of a subcarrier produced by dividing the clock frequency delivered by the detection means.

9. ^The portable object of one of claims 7 or 8, wherein the circuit is capable of two modes of operation in nominal consumption and low power consumption, and there is provided means for placing in low power mode the circuit before the data transmission means begin to operate said modulation.

10. The portable object of one of claims 1 to 9, wherein the detector means ^clock piloting communication protocols and / or signal processing and / or processing of data received.

11. ^The portable object of one of claims 1 to 10, further comprising means (288-296) switches the connection between electrical contacts (286) and other circuits of the portable object, controlled by the clock detector means so as to interrupt said link when the portable object communicates by contactless means.

12. The portable object of one of claims 3 to 11, further comprising, downstream of the rectification and filtering stages (210, 212), a stabilizing stage (216) comprising a shunt regulating element (228) mounted in parallel between the power ^supply terminals (VCC, GXD) of the circuit to be supplied and associated with a resistive component (230) mounted in series in the supply line of the circuit, the shunt regulating element taking and deriving a variable fraction of the supply current from the circuit so that the resistive element and the shunt regulating element dissipate any additional energy not necessary for the operation of the circuit, so as to correlatively stabilize the supply voltage (d) at the terminals of the circuit, limit the voltage excursion (a) to across the element provided upstream and prevent variations in the current consumed n ^'influence upstream on the amplitude of if- gnal to be demodulated.

13. The portable object of claim 12, comprising means (240) for selectively and temporarily inhibiting the operation of the shunt regulator.

14. The portable object of Claims 12 and 13 taken in combination, wherein ^the selective inhibition and temporary operation of the shunt regulator is operated in response to the detection of a type of communication via contacts.

15. The portable object of ^one of claims 1 to 14. wherein ^the entire electronic circuit (202, 204), with ^the exception of the coil (202) of the given element, is made of monolithic technology integrated.