Patent Description:
Integrated circuit cards, also known as smart cards or IC cards, are well known. It becomes increasingly frequent that IC cards operate both in contact and contactless mode. Recent developments of IC cards aim at equipping the cards with peripheral systems such as fingerprint sensors, dynamic readable verifying codes, display, etc..

Document <CIT> discloses a circuit and method for selecting a current powering.

Document <CIT> discloses an analog combination regulator.

There is a need for improvement of integrated circuit cards.

More particularly, there is a need for improvement of the power supply of a peripheral device included in an IC card.

One embodiment addresses all or some of the drawbacks of known IC cards.

The invention is defined by the annexed set of claims.

One embodiment provides a linear voltage regulator comprising:.

According to an embodiment, a voltage divider of the regulated voltage provides the third voltage.

According to an embodiment, the regulator further comprises a circuit having two inputs respectively coupled, preferably connected to said first and second input terminals and one output providing the fourth voltage.

According to an embodiment, said circuit comprises a comparator of the first voltage and the second voltage, which controls switches selectively coupling the first input terminal and the second input terminal to said output providing the fourth voltage.

According to an embodiment, said second voltage is a voltage extracted from an electromagnetic field.

An embodiment provides an integrated circuit card comprising a regulator.

According to an embodiment, the card, comprises:.

According to an embodiment, the card further comprises a first integrated circuit and an electronic system external to the integrated circuit, said regulated voltage being intended to supply said external system.

For the sake of clarity, only the operations and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail. In particular, the operation of an integrated circuit card or smart card, has not been detailed, the voltage regulator of the present disclosure being compliant with usual operation of such card.

<FIG> schematically represents an embodiment of an integrated circuit card.

An integrated circuit card <NUM>, or IC card, or smart card, to which apply the disclosed embodiments comprises:.

The IC chip <NUM> contains electronic circuits adapted to the application of the card <NUM>. For example, chip <NUM> comprises a microcontroller adapted to operate and control the other elements of card <NUM> depending on the application.

A card <NUM>, as illustrated in <FIG> is usually designated a dual interface smart card. The card has two interfaces: One contact interface to communicate with a contact reader and one contactless interface to communicate with a wireless reader (NFC or the like). Depending on whether the card <NUM> is inserted in a contact reader or is located within the range of a contactless reader, its electronic circuits are powered via the contact interface or via the wireless interface (via the field generated by the contactless reader).

To render the operation of the card <NUM> compliant with both contact power supply and contactless power supply, chip <NUM> usually comprises voltage regulators capable of providing supply voltages to the rest of the chip <NUM>.

The increase of the functionalities of IC cards and of the number of embedded electronic components, such as external (to the chip <NUM>) systems or circuits <NUM>, increases the power requested by the card to operate. Both contact and contactless readers are capable to provide such increased powers. However, the size of the voltage regulators integrated to the card becomes increasingly important.

Additionally, dedicated regulators should be provided for such external or peripheral circuits <NUM> as their requested voltage level can be different than those of the main circuit (microcontroller) of chip <NUM>.

An example of application is a banking card with fingerprint sensor.

Another example of application is a banking card with a display of a changing card verification value (cvv).

Still another example of application is a card (not necessarily a banking card) with a sensor such as a fingerprint sensor, a temperature sensor, an image sensor, etc..

Still another example of application is a card with a display, for example a counter value display or an image display, etc..

In such applications, the external circuit <NUM> is a sensor such a fingerprint sensor, a temperature sensor, a cvv display, counter value display, an image display, etc..

The value of the power voltage used by the external embedded system or circuit <NUM> depends on the application.

However, it is desirable to provide a single integrated circuit <NUM> capable of providing the appropriate voltage to various external circuits <NUM> in order to increase mass-market production of the main integrated circuit <NUM>, which can then be used for different applications depending on the nature of the external circuit <NUM> of the card.

<FIG> illustrates, schematically and partially, an embodiment of a power supply architecture of a dual interface integrated circuit card.

The dual interface circuit card <NUM> comprises a voltage regulator <NUM> (REG) for regulating a voltage VCC provided by a contact reader (not shown) or a voltage VCC_CL extracted from the field generated by a contactless reader (not shown).

When the card <NUM> is inserted in a contact reader, the dc voltage VCC is present between two contacts <NUM> and <NUM> of the contacts <NUM> (<FIG>) of the card. Two inputs of the regulator circuit <NUM> are respectively coupled, preferably connected, to the contacts <NUM> and <NUM>.

When the card <NUM> is in the range of a contactless reader generating an electromagnetic field, an oscillating circuit of card <NUM>, comprising the antenna <NUM> and a parallel capacitor <NUM> (integrated or not in circuit <NUM>), extracts a signal from the field generated by the reader. Terminals <NUM> and <NUM> of the oscillating circuit are coupled, preferably connected, to a rectifier <NUM>, which extracts a dc voltage VCC_CL from the signal present at terminals <NUM> and <NUM> of the oscillating circuit. Two inputs of the regulator circuit <NUM> are respectively coupled, preferably connected, to rectified outputs <NUM> and <NUM> of the rectifier <NUM>. In practice, these outputs are also connected by a capacitor Cin.

When operating in contact mode, other terminals <NUM> of the card <NUM> are used by the integrated circuit <NUM> to communicate with the contact reader.

When operating in contactless mode, the integrated circuit <NUM> communicates with the contactless reader via antenna <NUM>. For this purpose, communication circuits (no shown) of circuit <NUM> are coupled to the terminals <NUM> and <NUM> of the oscillating circuit.

The functional operation of the card in contact mode or in contactless mode will not be further detailed as the present disclosure concerns the power supply of peripheral device <NUM> of the card <NUM> and more particularly the regulation of the voltage provided in contact mode or in contactless more.

An output <NUM> of regulator circuit <NUM> provides a regulated voltage VCC_OUT to the external system <NUM> of card <NUM>. The regulated voltage VCC_OUT is, arbitrarily, positive with respect to ground <NUM> provided either by terminal <NUM> in contact mode of by terminal <NUM> in contactless mode.

The value of the regulated voltage VCC_OUT depends on a value of a reference voltage VREF provided to the regulator <NUM> by another element (for example a bandgap) of the integrated circuit <NUM> (not shown).

The value of the regulated voltage VCC_OUT depends on the application and more particularly to the type of external circuit <NUM>. As a specific example, the value of the output regulated voltage VCC_OUT can range from <NUM> volts to <NUM> volts and can take more than <NUM> different values in this range depending on the application.

<FIG> illustrates, schematically and partially, an embodiment of a voltage regulator of an integrated circuit card.

The regulator <NUM> is a linear regulator or Low Drop-Out (LDO) regulator. Power transistors of the regulator <NUM> couple the respective input terminals of the voltages to be regulated to the output terminal providing the regulated voltage.

In the exemplary embodiment of <FIG>, transistors <NUM> and <NUM> are MOS transistors (preferably PMOS transistors). Respective sources <NUM> and <NUM> of transistors <NUM> and <NUM> are coupled, preferably connected, to terminals <NUM> and <NUM>. Respective drains <NUM> and <NUM> of transistors <NUM> and <NUM> are coupled, preferably connected, to output terminal <NUM>. Respective gates <NUM> and <NUM> of transistors <NUM> and <NUM> are coupled, preferably connected, to the input stage <NUM> of the regulator <NUM>.

According to the disclosed embodiments, both power transistors <NUM> and <NUM> of regulator <NUM> share a common input stage <NUM>.

<FIG> schematically details an embodiment of the regulator <NUM> of <FIG>.

The input stage <NUM> of the regulator <NUM> comprises an error amplifier <NUM>, or gain stage, of the difference between a feedback voltage VFB, proportional to the regulated output voltage VCC_OUT, and the reference voltage VREF. The amplifier <NUM> provides, at an output <NUM>, an analog signal, function of this difference between voltages VCC_OUT and VREF, to control the gate <NUM> or <NUM> of transistor <NUM> or <NUM>.

The reference voltage VREF, provided by the circuit <NUM> is applied to an input <NUM> of the amplifier <NUM>.

The feedback voltage VFB, proportional to the value of the output voltage VCC_OUT, is provided by a feedback voltage divider <NUM> receiving the output voltage VCC_OUT and providing the voltage VFB to an input <NUM> of the amplifier <NUM>. In the example of <FIG>, the voltage divider <NUM> is made of two resistors R1 and R2 connected in series between the output terminal <NUM> and ground <NUM>, the mid-point of the series connection forming the output of the voltage divider <NUM> providing the feedback voltage VFB.

According to an embodiment, the value of the referenced voltage VREF is fixed and do not depend on the voltage requested by the external system. Resistors R1 and R2 are then, for example, trimmable resistors, which are trimmed according to the application (depending on the value of the supply voltage of the external circuit <NUM>) to select the value of the output voltage VCC_OUT. According to another example, the voltage divider is made of a network of controllable resistors, configured by the microcontroller <NUM> (<FIG>) based on the desired supply voltage for the external circuit <NUM>.

According to another embodiment, the value of the reference voltage VREF is provided by the microcontroller <NUM> of integrated circuit <NUM> depending to a personalization of the circuit. Resistors R1 and R2 can then have fix values.

As it can be seen from <FIG>, the regulator <NUM> comprises only one feedback resistor chain, which is used in both operation modes.

In order to select the transistor <NUM> or <NUM> to be controlled by the error amplifier <NUM>, switches <NUM> and <NUM> are provided between the output <NUM> of the amplifier <NUM> and the respective gates <NUM> and <NUM> of transistors <NUM> and <NUM>. The switch <NUM> couples the terminal <NUM> to the gate <NUM> of the transistor <NUM> and the switch <NUM> couples the terminal <NUM> to the gate <NUM> of the transistor <NUM>. The switch <NUM> is controlled to be fully on or fully off by the enabling signal EN_CL. The switch <NUM> is controlled to be fully on or fully off by the enabling signal EN_CNT. The selection of the switch <NUM> or <NUM> to be on is made by the microcontroller <NUM> depending on the selected operation mode (contact or contactless).

According to a preferred embodiment, the regulator <NUM>, and more particularly its input stage <NUM>, comprises a circuit <NUM> (Max of VCC and VCC_CL), which selects the maximum or highest voltage between voltages VCC and VCC_CL and provides, at an output terminal <NUM> of circuit <NUM>, this maximum voltage as an internal supply VCC_LDO. A capacitor C6 couples terminal <NUM> to ground <NUM>.

The error amplifier <NUM> is supplied by the voltage VCC_LDO. This ensures a correct biasing of the bodies (bulks) of the transistors of the gain stage. This also guarantees a correct excursion of the control signal provided at the amplifier output <NUM>.

Additionally, the bodies of the PMOS transistors <NUM> and <NUM> are biased by the voltage VCC_LDO. This avoids a conduction of the parasitic diodes of the transistor <NUM> or <NUM>, which is not in operation if the output voltage VCC_OUT is higher than the source voltage of that transistor.

According to a preferred embodiment, the gate of the transistor <NUM> or <NUM> which is not in operation, is pulled up to the maximum voltage VCC_LDO between VCC and VCC_CL. This guarantees a null or positive gate-source voltage (Vgs) of the corresponding transistor, i.e., an off state of that transistor, which is therefore not leaking whatever is the value of its source voltage.

According to the preferred embodiment represented in <FIG>, The respective gates of transistors <NUM> and <NUM> are coupled to the output terminal <NUM> of circuit <NUM> by switches <NUM> and <NUM>, respectively controlled by the inverses of signals EN_CNT and EN_CL. The signal EN_CNT is applied, via an inverter <NUM>, to the control terminal of switch <NUM>. The signal EN_CL is applied, via an inverter <NUM>, to the control terminal of switch <NUM>.

According to another embodiment, the respective gates of the transistors <NUM> and <NUM> are coupled to terminal <NUM> via pull-up resistors.

<FIG> schematically details one embodiment of the circuit <NUM> of the voltage regulator <NUM> of <FIG>.

A comparator <NUM> has its input terminals respectively coupled, preferably connected, to the terminals <NUM> and <NUM> providing the voltages VCC and VCC_CL. For example, the noninverting (positive) input (+) of the comparator <NUM> is coupled, preferably connected, to terminal <NUM> and the inverting (negative) input (-) of the comparator <NUM> is coupled, preferably connected, to terminal <NUM>. In this example, the output of the comparator <NUM> is high if the contact voltage VCC is higher than the contactless voltage VCC_CL and is low if the contactless voltage VCC_CL is higher than the contact voltage VCC. The comparator <NUM> controls two switches <NUM> and <NUM> respectively coupling the terminals <NUM> and <NUM> to the output terminal <NUM> providing the selected voltage VCC_LDO. For example, the output of the comparator <NUM> directly controls switch <NUM> and controls, via an inverter <NUM>, switch <NUM>.

A supply voltage VCC_AUX of the comparator <NUM> is provided by an auxiliary power supply, based on the highest voltage between VCC and VCC_CL. To this purpose, terminals <NUM> and <NUM> are respectively coupled, via diodes <NUM> and <NUM>, to the positive supply terminal of comparator <NUM>. The anodes of the diodes <NUM> and <NUM> are respectively coupled, preferably connected, to terminals <NUM> and <NUM>. The cathodes of the diodes <NUM> and <NUM> are coupled, via a capacitor <NUM> to ground.

Using an internal voltage VCC_LDO corresponding to the highest voltage between VCC and VCC_CL, is particularly useful in the application to a contactless system. Indeed, the value of the voltage VCC_CL is variable and can be higher or lower of the voltage VCC depending on multiple factors such as the distance form a reader, some perturbations of the field generated by the reader, etc. Additionally, while the voltage VCC is only present when the card is inserted in a contact reader, an electromagnetic field can be present and captured by the antenna <NUM> (<FIG>) anywhere.

The switches <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, which are on/off switches, can be made of MOS transistors. The sizes of these transistors can be much lower than the size of transistors <NUM> and <NUM> as the vehiculated power is much lower. This is in particular true for switches <NUM>, <NUM>, <NUM> and <NUM>. For switches <NUM> and <NUM>, the power is a bit higher than those of switches <NUM> to <NUM> as they should be capable of powering the error amplifier <NUM>. However, this stays much lower than the power of transistors <NUM> and <NUM>.

An advantage of the disclosed embodiments is to reduce the area occupied by the power regulating system with respect to conventional cards using two distinct linear regulators.

Another advantage of the disclosed embodiments is that the sharing of the input stage <NUM> of the regulator <NUM> for the contact mode and the contactless mode drastically reduces the testing time needed for the chip. This is in particular the case for cards requiring different output voltage options.

Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these embodiments can be combined and other variants will readily occur to those skilled in the art. In particular, the voltage regulator proposed in the present disclosure has been detailed in relation with an example of application to an integrated circuit card but more generally applies to any wire and wireless device to which similar problems arise.

Claim 1:
A linear voltage regulator (<NUM>) comprising:
a first transistor (<NUM>) between a first input terminal (<NUM>), adapted to receive a first voltage (VCC), and an output terminal (<NUM>) adapted to provide a regulated voltage (VCC_OUT);
a second transistor (<NUM>) between a second input terminal (<NUM>), adapted to receive a second voltage (VCC_CL), and said output terminal;
an amplifier (<NUM>) of the difference between a third voltage (VFB) proportional to the voltage at said output terminal, and a reference voltage (VREF), an output (<NUM>) of said amplifier being selectively coupled to respective control terminals (<NUM>, <NUM>) of said first and second transistors, said amplifier being supplied by a fourth voltage (VCC_LDO) corresponding to the highest voltage between said first and second voltages,
the linear voltage regulator (<NUM>) is characterized in that said output (<NUM>) of the amplifier (<NUM>) is coupled by a first switch (<NUM>) to the control terminal (<NUM>) of said first transistor (<NUM>) and by a second switch (<NUM>) to the control terminal (<NUM>) of the second transistor (<NUM>), said first and second switches being respectively controlled by first (EN_CNT) and second (EN_CL) control signals,
wherein the control terminal (<NUM>, <NUM>) of each of the first and second transistors (<NUM>, <NUM>) is pulled-up to the fourth voltage (VCC_LDO), and
wherein a third (<NUM>) and a fourth (<NUM>) switches respectively couple the control terminals (<NUM>, <NUM>) of the first and second transistors (<NUM>, <NUM>) to the fourth voltage (VCC_LDO), the third and fourth switches being controlled by the respective inverses of the first and second control signals.